FAQ PAGE

GENERAL FAQ

RCD received UL recognition for a limited range of products however the safety considerations of UL (or CSA, VDE, etc) regarding resistors, capacitors, and inductors depend largely on how the component is utilized in the circuit. As such, our customers generally get the entire circuit UL recognized not each of the individual components. RCD can obtain UL recognition on particular products on an as-needed basis (associated UL test & maintenance costs are borne by customer).  If helpful, please note that the insulation material of our standard resistor, capacitor, and inductor products meets UL-94V1 flame retardancy (some products are UL-94V0). Products designated as "flameproof" or "fusible" meet UL-94V0. These ratings are based on testing by RCD and/or our coating/molding material suppliers.

As is common in the industry, RCD strives to ship exact quantities but in order to keep our selling prices low, there are instances when we might ship a small amount more or less than the ordered quantity. This is especially true on difficult and specialty items, small quantities, and rush shipments.   If we “cut it too close” in terms of the production quantity, we would sometimes need to produce an additional lot to make up for any shortages. The various set-up expenses throughout the production process on this additional lot would be very costly. In order to prevent these extra costs, small quantity allowances are allowed. RCD’s standard terms concerning over/under shipments allows us to close orders within ±3% of the ordered quantity, ±5% (or 1 piece) if ≤500 pieces, and ±10% on SWIFT™ orders. Please determine your quantity requirements accordingly. In the event that RCD’s standard terms and conditions are unsatisfactory, please let us know your requirements in advance so that we can quote appropriately (tightened allowances typically add 5% to 10% to unit prices).

Yes, RCD has been manufacturing components for nearly 40 years under the “RCD” brand as well as on private label basis for other component companies. We have no plans to reduce our capacity or capability. Actually, quite the contrary, since we are increasing capacity levels.

 

Production plants are wholly or partially owned by RCD (or the owners of RCD). In addition, some products (such as carbon resistors in finished or unfinished form) are produced for RCD via strategic alliance. In this case, control over quality and delivery performance is achieved via contractual requirements, product traceability, inspection at the production plant and reinspection at RCD, as well as “locked” materials and manufacturing processes.  

 

RCD’s USA plant manufactures primarily smaller quantities and SWIFT orders, as well as precision, custom, military and aerospace products. Low-cost volume efficiency is achieved at Caribbean and Asian facilities.

 

All products are ISO9001 certified. In addition, RCD is certified supplier to U.S. Defense Department, NATO, NASA, and is sanctioned to AS-9000 (Aerospace Quality System). RCD’s QA system is fully compliant (although not formally certified) with automotive standards QS-9000 and TS-19649. Redundant manufacturing capability is maintained on most products to ensure a steady supply, even in the event of natural disaster or other unforeseen circumstance.

 

RCD retains manufacturing and inspection records, and traceability is achieved by lot or date code marked on parts (or packaging). Test reports, certificates-of-compliance, and certificates-of-origin are available with each shipment.

The best way to avoid receiving counterfeit parts is to buy products through RCD-authorized channels. View our list of Representatives and Distributors now or Contact Us directly.

Yes, RCD maintains manufacturing records for a minimum of two years, and longer by pre-arrangement with the customer.

 

Military parts are typically marked with a Year/Week date code in accordance with the particular Mil-spec. The date code is typically comprised of 4-digits, the first two representing the year, and the second two the week. 

 

For example, “0719” indicates that the parts were made during the 19th week of 2007.

 

Commercial parts include an internally-generated lot number on the packaging, which gives RCD traceability to the inspection records. Some alpha-numerically printed commercial parts also have a manufacturing lot number marked on the component body (when space and process conditions permit). The lot code is typically comprised of a pre-assigned 6 or 7-digit alpha-numeric combination.

 

In the unlikely event of a quality problem, or for general date/aging purposes, RCD staff can research lot numbers and cross reference to the pertinent inspection/production lot. Customers that have any particular marking, labeling, traceability, or record-keeping requirements should discuss with RCD.

Yes, a lead-free version is available on almost all of our products (resistors, capacitors, inductors, delay lines). You simply need to add Option W to the part number (i.e., MC0603W, PW10W, etc.). For additional information refer to the RoHS section of RCD’s website.

Yes, a tin-lead (SnPb) version is available on most products, intended primarily for military, space, and medical customers. Specify Option Q at the end of the part number.  Depending on the product, there may be a small price premium associated with this option, especially in small-to-medium sized orders.

Opt 25 isn't necessary for most applications. Opt 25 is specified primarily by military subcontractors who need essentially perfect solderability even after extended storage periods.

Refer to Engineering Report R-37 for details

In order to keep terminations “fresh” to facilitate the soldering process, customers should adhere to the following guidelines:

 

  1. Try to control purchases and inventory levels so that stock is replenished every two years or less, following a FIFO (first-in first-out) policy. In most instances the actual usability of components is much longer than 2 years and in fact can reach a decade or longer however this depends on the storage conditions and component processing (i.e. plating thickness, solder alloy, etc.).
  2. Store parts in sealed poly bag including a packet of desiccant.
  3. Store in cool/dry location. In order to maintain optimum solderability for extended periods, parts should be stored in an inert atmosphere. Specialty nitrogen-based desiccator cabinets are available for this purpose at terrauniversal.com and other similar firms.
  4. Another option is to arrange for RCD or one of its distributors to stock the various items and replenish customer stock on an as-needed basis.

“Popcorn effect” is a problem that generally occurs when a component is mounted to a PC board via wave or infrared soldering techniques. The rapid heating associated with these procedures causes moisture in the package to vaporize. The resulting pressure exceeds the yield strength of the epoxy (or silicone) mold compound and may cause electrical or physical damage.  Electrical damage may be detected as an open or intermittent contact. Visual defects may not be obvious, but may include cracked package, missing package material, bulging or deformed package. Visual anomalies do not necessarily imply device failure. In some instances, the component forcefully detaches itself from the PC board… i.e., “pops” off the PCB.

As a manufacturer specializing in customized components, RCD offers an incredible range of product options. These options number into the hundreds and include a wide range of specialty termination platings, lead wire sizes and formations, custom markings/colors/coatings/testing/burn-in, non-magnetic designs, low thermal-emf designs, etc. In addition, RCD offers numerous design modifications to enhance performance under a variety of conditions such as temperature or humidity extremes, harsh solvents, salt, or acidic environments/ high frequency, voltage, current, power, surge, dielectric strength, creepage, flame retardance, vibration, etc. Since most of these options are rather obscure, we only list the most popular ones on the catalog data sheet. If a customer actually needs an official “spec sheet” listing the option (such as for UL certification), RCD’s Sales Department can prepare one.

LEAD FREE POLICY FAQ

RCD offers RoHS-compliant construction on essentially all of its products, ensuring that RoHS restricted substances are not present or limited to 0.1% of lead, mercury, hexavalent chromium, PolyBromoBiphenyls, PolybromoDiphenylEthers, and 0.01% of cadmium.

Yes, RCD added a termination code at very end of each p/n. “W” indicates lead-free, “Q” indicates Tin/Lead.

RCD switched most of its products during the 2002 - 2004 timeframe (some products have always been lead-free).

RCD employs pure matte tin (Jedec code e3) for the plating material of most of its products. Some specialty and power components products utilize gold (e4), palladium silver (e4), SnCu (e2), or SnAgCu (e1). For customers requiring traditional tin/lead plating, RCD continues to offer this as an option on most products.

Yes, tin is compatible with popular Sn/Pb solder assembly processes. The vast majority RCD’s RoHS compliant products are forward and backward compatible with no change in form, fit or function.  Our applicable products are compatible with the higher temperature requirements of typical lead-free solders, i.e. 260 deg C vs. 230-235 deg C.  Some products (such as delay lines, magnetics and some specialty  resistors & capacitors) are not recommended for high temperature processing.

 

 “Forward compatibility” means our products with SnPb plated terminations are compatible with conventional Pb-based solders (60/40 & 63/37) as well as Pb-free solders(Sn/Ag & Sn/Ag/Cu).  “Backward compatibility” means the new Pb-free products can be used with conventional Pb-based technologies. If specialty high-temp solders are utilized, such as Pb85 and HMP, RCD can provide prototypes for evaluation.

 

Tin plating has fairly similar solderability, shelf life and electrical performance as traditional tin-lead plating.  As such, customers can phase in the use of lead free components prior to converting to a lead free solder process.  BGA devices (Ball Grid Array) are the exception to the above.  RCD does not consider lead-free BGA’s to be backwards compatible... higher solder process temperatures are required to ensure adequate solder joint reliability in lead-free BGA devices.

RCD has changed p/n designation to include termination code so that customers can readily identify the product. Termination code “W” indicates lead-free. .

No, this was phased in over a multi-year period.

Yes. For some products where inventory exists of non-leadfree products, RCD will continue to ship these unless a customer specifically requests termination “W” lead-free design.

There was a cost adder on some products initially. At this point there isn’t a cost adder and in fact, customers that require Tin/Lead plating (option “Q”) will likely experience rising costs as these products become less popular.

Customers who don’t require a specific type can leave the termination code blank when requesting pricing and availability, or when placing orders. This way, RCD’s staff will select the parts which offer best pricing and/or availability.

There are no expected changes in electrical performance or reliability of RCD's products due to the change to leadfree plating.

Yes, test summaries are available to customers. Please contact info@rcdcomponents.com.

Yes RCD can assist by supplying recommended solder profiles, etc.

RCD continually reviews it's product lines to ensure that active products are maintained. There are occasions where limited sales may be the cause for obsoletion. Leadfree processing will not directly cause the obsoletion of any RCD part numbers, but may prompt a review of the sales history of each part to ensure that there are active sales.

Whisker growth is believed to result from stress imparted to the tin layer.  Electroplated stress is linked to high plating currents & rapid electroplating process. RCD’s electroplating processes are optimized accordingly. In addition, RCD utilizes tight controls on tin purity and plating thickness, and achieves good match of CTE when electroplating Tin (Sn) onto Nickel (Ni) or Copper (Cu). The process of preconditioning the tin plating (heating and cooling) relaxes the molecular lattice structure eliminating stress. Here’s a summary of the controls utilized on RCD’s MC series of chip resistors to prevent whiskering-…

  1. Matte Sn finish
  2. Heavy Ni barrier thickness
  3. A precisely controlled plating process for:
    1. plating bath parameters: current density, voltage, acidity,
    2. plating bath chemistry and material contamination
    3. plating thickness
    4. plating stress
    5. plating grain size (large grains reduce whiskering)
    6. plating crystallographic texture (well polygonized)
    7. plating carbon content typ.below 0.05% and copper content typ. below 0.5%
NOTE: Tin (Sn) plated component terminations utilizing low temperature conductive adhesive, remain a risk for whisker growth. As such, it is recommended that customers utilize RCD’s palladium silver terminations when using conductive epoxy instead of soldering technology.

Please contact your local representative to request samples or contact our sales department at 603-669-0054 sales@rcdcomponents.com.

For further technical inquiries and information, please contact RoHS@rcdcomponents.com.

Yes, our components are designed to be compatible with all common leadfree solder alloys.

No, there can be trace elements of lead in accordance with RoHS limitations (0.1% max). In addition, there are exemptions for lead in some products, such as thick film materials. For more information about exemptions on a particular part number or product family, please contact RCD (rohs@rcdcomponents.com)

Electronic devices encapsulated or coated with plastic compounds and organic materials, absorb moisture. Humidity enters the package by diffusion, collecting at dissimilar material interfaces.

Device sensitivity to moisture is classified by Moisture Sensitivity Level (MSL) in accordance with IPC/JEDEC J-STD-020B. Rapid heating during soldering creates internal vapour pressure

and accelerated expansion within the device. Higher temperatures associated with lead-free processes can compromise moisture resistance particularly where existing procedures were marginal. RCD doesn’t anticipate any changes in the Moisture Sensitivity Classification for the vast majority of its products. The list of parts (if any) will be made available on the RCD website as testing is completed. Moisture sensitivity levels are ranked from level 1 (most resistive to moisture) to level 5 (least resistive to moisture). The vast majority of RCD’s products are classified as MSL-1, indicating that no special anti-moisture packaging or handling is required.

JEDEC Standard No. 97 has developed a series of Pb-Free categories to describe the 2nd level interconnect terminal finish/material of components and/or the solder paste/solder used in board assembly.

CategoriesType
e1SnAgCu (shall not be included in category e3)
e2Sn alloys with no Bi or Zn (i.e., SnCu, SnAg, SnAgCuX, etc.) excluding SnAgCu
e3Sn
e4Precious metal (e.g., Ag, Au, NiPd, NiPdAu) (no Sn)
e5SnZn, SnZnx (no Bi)
e6contains Bi
e7low temperature solder (≤ 150 °C) containing Indium (no Bi)
e0, e8, e9symbols are unassigned

CAPACITOR FAQ

"Aging" refers to the natural process wherein X7R, X5R, Z5U & Y5V ceramic capacitors exhibit a drop in capacitance and dissipation factor over time. It is caused by a gradual realignment of the crystalline structure of the ceramic. To reverse this shelf life aging effect, the parts can be “deaged” by baking parts at +125ºC for 4 hours or ½ to 1hour at +150ºC. This will result in parts increasing in capacitance and returning closely to their original value. It should be noted that parts which are deaged and then subjected to temperatures above the curie point (typically +120ºC), such as soldering and temperature cycling, may shift up in value slightly.  As the temperature is later reduced below the Curie point, the capacitance gradually returns to its previous values. Aging occurs at a rate that decreases roughly linearly with the log of time. NPO/C0G and tantalum capacitors have a different molecular structure which is essentially immune to aging and therefore they remain quite constant with time.

 

The aging rates are somewhat proportional to the dielectric constant or permittivity of a materials and are typically expressed as a percent per decade hour (i.e. 1-10 hours, 10-100 hours, 100 - 1000 hours, etc. Aging occurs quickly at first and then much more slowly over time.  Maximum aging rates are as follows:
 

Maximum % Capacitance Loss/Decade Hour

X7R - 2.0%
X5R - 2.5%
Z5U - 7.0%
Y5V - 7.0%
(actual rates may be lower)
 

Because the capacitance changes rapidly just after deaging, capacitance measurements are delayed for 24 hours (referred to as "last heat").

Parallel: When connected in parallel, the total capacitance is equal to the sum of the individual capacitance values. When connected in series, the total capacitance is lowered to the reciprocal level (exactly the opposite of resistors). For example, if three capacitors of values 1.0µF, 0.10µF, and 0.010µF are connected in parallel, the total capacitance would be:

 

C = C1 + C2 + C3 = 1.0µF + 0.10µF + 0.010µF = 1.11µF

 

The voltage rating of the parallel capacitors is only as high as the smallest voltage rating of the group, if they aren't equal.  If they are equal, the voltage rating is the same as that of a single capacitor.

 

Series: If the same three capacitors are connected in series, add their reciprocal values, as follows:

 

1/C = 1/C1 + 1/C2 + 1/C3 = 1/1 µF + 1/0.1µF + 1/0.01µF = 1/0.009, therefore C = 0.0090µF

 

The voltage rating of the series capacitors is equal to the sum of the voltage ratings of the individual capacitors if they are the same value.  If the capacitors are of different values, and are used in an AC circuit, the voltage division will not be equal.

 

AC Voltage Divider: Capacitive dividers can be used with AC input signals.  Since a DC input voltage wouldn’t pass through the capacitors, the DC case isn’t relevant.  The formula for determining the AC output voltage of a capacitive divider is as follows:

 

Vout = (Vin * C1) / (C1 + C2)

 

Example:  In the following circuit, the output voltage would be:  Vout = (10VAC x 0.050µF)/(0.050µF + 0.010µF) = 8.333VAC.  The output voltage is typically not dependent on the input frequency however, if the reactance of the capacitors is too low at the frequency of interest, the output current capability will also be very low.

Schematic

On a Tantalum capacitor with radial leads (RCD TR Series), the long leg lead is always the positive or anode lead on the capacitor. The capacitor should also have the polarity marked on the capacitor. The exception to this is a non-polar capacitor (such as RCD’s CEA or CER Series ceramic capacitors) which will have no polarity marking on them. Non-polar capacitors may still have different lead lengths but this does not indicate any polarity orientation.

Class 2 (X7R, X5R) and Class 3 (Y5V,Z5U) ceramic capacitors have problems not seen in Class 1 (NPO, COG) and film capacitors, including very poor temperature drift, high voltage-coefficient-of-capacitance and, high voltage-coefficient-of-dissipation factor (all of these are different for AC and DC), high frequency-coefficient-of-capacitance and a significant aging rate. Class 2 capacitors are best suited for coupling (DC blocking) and power supply bypassing.  They are primarily used in linear applications where performance and stability are of no great concern.  Class 3 capacitors should be used only for DC blocking and bypassing. The change in capacitance due to aging, temperature coefficient, and voltage coefficient must be taken into account whenever using Class 2 or 3 caps, especially class 3.  For best performance, use the parts at a low percentage of rated voltage. Applied voltage affects some properties so much that these capacitors are normally characterized at no more than 1 volt AC or DC. The table below shows what happens to capacitance when DC voltage is applied to various ceramics.  Capacitance vs. AC voltage generally has the opposite result (capacitance increases in value).   The numbers are approximate and vary somewhat with capacitance value. Graph

Ceramic capacitors are quite reliable. Failures typically result from voltage overloads or mechanical stress. The most commonly reported cause of field failures is high leakage (i.e., low insulation resistance) usually attributable to microcracks. When high energy levels are involved, microcracks can result in catastrophic failure. Under lower energy levels, damaged chips could continue to function for a long time.  Circuit test equipment will generally only identify those caps with high leakage levels. The reason for this is because the crack (or more specifically the air gap in the dielectric resulting from the crack), acts as a capacitor, making the damage difficult to detect. Since the voltage stress is concentrated in the area of the crack, this degrades the bulk resistivity, propagating even higher leakage levels over time especially in conditions of high temperatures and humidity.

 

Causes of cracks are typically due to mechanical stresses (excessive board flex, shock/vibration impact from handling, testing, depanelization, pick & place pressure, etc.), or thermal stresses (excessive soldering temperature or duration, thermal expansion/mismatch). In addition to user-related problems
Failures can also result from:

  • improper surface conduction, i.e., entrapped flux under chip or external surface contamination (more common with "No clean" systems) result in shunt leakage paths.
  • Fractured terminations
  • High surge currents
  • Aging – the capacitance value typically decreases through the normal aging process on X5R, X7R, Z5U, Y5V dielectrics.
  • Voltage and temperature changes can also have a fairly significant affect on the capacitance value of these dielectrics resulting in parts which have temporarily shifted beyond the nominal tolerance band
  • Open/intermittent solder joints due to tombstoning, poor PCB or chip solderability, leaching of the termination plating, chip or solder placement, cold solder joints, etc.
  • Improper handling or processing by the capacitor manufacturer can result in cracks or voids in dielectric.
  • Improper labeling or sorting by manufacturer

Note: it is not uncommon for the nodal analysis by ICT (In-Circuit Test) equipment to falsely characterize a chip capacitor as being non-compliant when another component is actually at fault.

The 3-character designations describe how a particular type of ceramic capacitor will perform over its intended temperature range. See breakdown in following table. The code was assigned by the Electronic Industries Association (EIA).

 

Lowest Operating Temperature

Highest Operating Temperature

Maximum Allowable Capacitance Shift from 25ºC Readings

Without DC Bias

At 50% rated V

X = -55ºC

5 = 85ºC

R = +15/-15%

R = +15/-15%

Z = +10ºC

7 = 125ºC

S = +22/-22%

S = +22/-22%

Y = -30ºC

8 = 150ºC

U = +22-56%

U = +22-56%

  

V = +22/-82%

V = +22/-82%

Precision capacitors are identified as COG (also known as NPO) which indicates a worst case temperature coefficient of 30PPM/ºC (0.003%/ºC).

  1. Advise competitor’s part number or, if unavailable, advise whether it is a conventional thru-hole part (axial, radial or disc) or surface mount.
  2. Advise construction (ceramic, tantalum, etc.). If unknown, go to #3.
  3. Advise capacitance value (0.01µF or micro farads, 10nF or nano farads, etc.).
  4. Advise capacitance tolerance (“Z “or +80/-20%, 10%, 5%, etc.).
  5. Advise voltage rating (50V, 6V, etc.).
  6. Advise dielectric (if a ceramic). NP0/C0G, X7R, Y5V, Z5U, X5R, etc.
  7. Advise of any special electrical requirements (low ESR, low profile, marking, etc.).
  8. Advise of any special lead-forming if thru-hole.
  9. Advise of any special packaging requirements (bulk, tape/reel, etc.).

DELAY LINE FAQ

RCD originally offered active delay lines in two versions…  standard (operating temp range of 0º to +70ºC) and military (Opt. ER, -55º to +125ºC). Most of the +125ºC IC's (utilized inside the Opt ER delay lines) were discontinued resulting in product supply problems and exorbitant price increases.  In discussions with customers, it was determined that nearly all had no real need of such temperature extremes. Delay lines that would operate at a low range of -30º to -40ºC, and a high range of +80º to +85ºC would be perfectly suitable. In response, RCD developed an “industrial grade” version rated for operation at -40º to +85ºC (designated as option 39). Essentially all of our Opt. ER customers have switched to opt.39. Some of the special +125ºC IC's are still available but generally very costly so we don't recommend it them unless absolutely necessary.

INDUCTOR FAQ

Inductance increases as the frequency approaches the SRF (self-resonant frequency) level. Therefore, the inductance level measured at low frequency is typically lower than that at higher frequencies. Along the same lines, the measured reading on most commercial-grade LCR test equipment is lower than on RCD’s military-grade test equipment since parts are generally tested at lower frequencies when using LCR meters. The difference is typically 2% - 15% but can be greater. Therefore, it is recommended that customers correlate sample readings with RCD or specify the required test frequency.

 

Another reason for correlation is due to the fact that there can be a fairly wide variation in the values measured between different set-ups resulting from variations in lead wire length and shape, as well as the intrinsic accuracy, capacitance & inductance of the test equipment and fixtures. Low values, such as 1uH or below are especially sensitive to the parasitics in test fixturing as well as the otherwise minor differences in inductance attributable to lead length, etc.

When testing inductors, there can be a fairly wide variation in the values measured between different set-ups, primarily due to test frequency, lead length, leadwire shape, test fixture capacitance & inductance, and test instrument intrinsic accuracy and self-inductance.  Low values, such as 1uH or below are especially sensitive to the parasitics in test fixturing as well as the otherwise minor differences in inductance attributable to lead length, etc.

 

More commonly, the differences are attributable to the test frequency. Most of RCD’s inductors are measured at Mil-specified test frequencies (refer to data sheets). These frequencies (7.9MHz, 2.5MHz, 0.79MHz, 0.25MHz, etc) generally do not match the pre-set frequencies on most LCR meters (1MHz, 100KHz, 1KHz, etc.). Since inductance increases as the frequency approaches the SRF (self-resonant frequency) level, the measured reading on most LCR test equipment is lower than on RCD’s test equipment since parts are generally tested at lower frequencies when using LCR meters. The difference is typically 2% - 15% but can be greater. Therefore, it is recommended that customers “correlate” sample readings with RCD or specify the required test frequency.

Inductor amperage ratings are based on DC current. The AC current ratings are much lower, especially at higher frequencies. Designing AC inductors involves more factors. For instance, instead of dealing with resistance, AC inductor designs focus on impedance because the impedance is dominant over the DC resistance and varies with frequency. Material losses must also be accounted for. Another issue is the skin effect. When RF voltage is used the alternating current causes the current to migrate to the surface of the copper conductor. As a result, the center (core) of the conductor is barely utilized for carrying current. The best method to minimize the uneven heating associated with the skin effect is to utilize stranded instead of solid wire. For the same reason, high-frequency AC inductors are typically much larger in size than DC counterparts. RCD’s engineering group would need to know the voltage, current, frequency, and size constraints in order to determine the most appropriate design.

  1. Advise competitor part number or, if unavailable, advise whether it is a conventional through hole part (axial, radial, etc.) or surface mount
  2. Advise construction (wirewound, film, etc.). If unknown, go to #3.
  3. Advise inductance value (0.01 μh or micro henries, 10nH or nano-henries, etc.).
  4. Advise inductance tolerance (10%, 5%, etc.).
  5. Advise current rating (0.20A, 200mA, etc.).
  6. Advise of any special electrical requirements (max DCR, saturation current, etc.).
  7. Advise of any special lead-forming (0.40" radial, etc.).
  8. Advise of any special packaging requirements (bulk, tape/reel, etc.).

RESISTOR FAQ

Carbon comp resistors can shift in value from overheating so yes, they might be overheating during your soldering process. They also increase in resistance due to moisture absorption. Refer to Table 1 for the recommended preconditioning schedule to bake out the moisture. Lastly, carbon comp resistors can also shift up quite a bit if excessive strain is applied to lead wires (such as using a bending tool or machine that doesn’t provide strain relief, bending too close to body, etc.).

 

Carbon comp resistors are great for withstanding power overloads but unfortunately are more sensitive than most other resistors in regard to environmental or physical factors such as temperature, humidity, lead stress, etc. Try to minimize soldering heat and moisture absorption but most importantly, be careful not to impart any stress inside the body when forming the leads or mounting to PCB.

 

If the carbon comp resistor doesn’t meet the stability requirements of the circuit, contact RCD engineering to determine whether there’s another resistor construction available that will meet all the requirements. If surge is involved this might require a larger body size.

As carbon composition resistors absorb moisture their resistance increases over time, as the resistor approaches saturation. Under high humidity conditions it is not unusual for parts to increase 6% in resistance in as little as 72 hours.

 

As the carbon compositions are dried their resistance decreases over time. Reversing the effect of moisture on the part’s resistance is accomplished by storing them in a controlled low humidity area or by conditioning them in a convection oven at 100°C.

 

RatingConditioning time @ 100°C
1/8W25 hours
1/4W50 hours
1/2W75 hours
1W120 hours
2W130 hours

image1image2
Concave Terminations
(RCD CN Series)
Convex Terminations
(RCD SMN Series)

Chip arrays are available in two styles (as illustrated above). The concave chip arrays (RCD CN series) have recessed terminations whereas the convex arrays (SMN series) have protruding terminations. Some resistor manufacturers offer only one type and some offer the other (more offer convex than concave).


Some customers prefer one type, some the other (convex is more popular). RCD originally offered only the convex version (1985) but later developed the concave version (1991) in order to meet the requirements of all customers. The convex version is generally the lower-cost version resulting from greater popularity and higher production volumes.

 

Some customers prefer the convex version due to larger clearance between terminations (typically 0.3mm vs. 0.25mm) which reduces the likelihood of solder bridging and short circuits. Another advantage of the convex termination is that optical inspection is faster and easier since the terminations are clearly visible instead of being embedded within the outline of the chip.

 

Some customers have found that the concave geometry offers superior self-alignment of skewed components during reflow soldering, yet others have found that the larger termination area of convex parts enhances self-alignment. RCD doesn’t take a position in which is “better” but can offer samples of both for customer evaluation.

Operation at high altitudes can cause increased self-heating as well as corona and arcing, especially if moisture is present. All of RCD’s standard catalog resistor models will operate at altitudes of 50,000 feet (equates to a pressure of 3.44 inches of mercury). Some models are available to 100,000 feet or higher (0.315 inches of mercury). When standard resistors aren’t suitable, RCD can generally offer custom-designed options for operation at even greater altitudes. RCD’s Test Lab can perform specific test screening for customers using precision vacuum equipment.

 

Since performance is affected by altitude, the general rule of thumb recommended by RCD to ensure safe and reliable operation is to derate the power/voltage/current ratings by 10% to 20% per 10,000 feet.

 

As for depths below sea level, RCD has not evaluated products but has been advised that various resistors function well at -500 ft (30.47 inches of Hg).

Resistors specifically designed for high surges are best, such as composition styles are best (refer to RCD series CC, PR, PRM, PCN). Without going to a specialty resistor the customer should concentrate on wirewound resistors, followed by thick film resistors. Thin film resistors tend to be the most sensitive although they are generally OK in most applications. Larger sizes enable greater ESD capability. RCD specializes in pulse-tolerant resistors and can assist in product selection.

No, only those resistors with a suitably high resistance value (at or above the “critical resistance value”) may be operated at the maximum voltage rating.

 

Most resistors carry a RCWV (rated continuous working voltage) rating, also known as the Maximum Voltage Rating. This is the maximum DC or ACRMS (or ACPEAK on some resistor types) voltage that the resistor size is designed to withstand across its terminals, or across its internal construction. The actual working voltage for a particular part and resistance value is determined by the formula E=(PR) 1/2 , E (voltage) not to exceed the maximum RCWV.

 

For a given voltage and a given power rating there is only one value of resistance that will dissipate full rated power at rated voltage. This value of resistance is commonly referred to as the “critical resistance”. For values of resistance below the critical value, the maximum (element) voltage is never reached and, for values above the critical value, the power dissipated becomes lower than rated. As such, the resistor power and voltage ratings are an  “either/or” rating, i.e. resistors are limited by their power rating (typically lower resistance values) or by their voltage rating ( higher values), whichever is less. 

 

Example: RCD type MC1206 20,000 ohm chip resistor has a power rating of 0.25W and a Max Voltage Rating of 200V. Can the part be operated at 200V? The answer is “no” because 200V across 20,000 ohms equates to 2 watts (P=E2/R so P=2002/20,000= 2 watts). At 200V the parts would quickly overheat since this is 8 times the wattage rating! The actual working voltage of MC1206 100 ohm is determined by E=(PR) 1/2 or (.25 x 20,000)1/2 = 70.7V.

 

RCD offers a wide range of customized voltage options via use of specialty materials and designs if the standard voltage rating isn’t adequate. These specialty designs can typically offer 50% to 200% increases in voltage levels above standard models.

Unless specifically prearranged before ordering, there is no guaranteed resistance tracking/matching level. Parts with an absolute tolerance of 1% therefore will track within a range of 2% (i.e. - 1% to +1%). Nothing better is guaranteed or implied. In actuality though, if all parts are manufactured at same time under the same conditions, the distribution will typically follow a somewhat normal bell curve, i.e., fairly normal Gaussian kurtosis approximately centered on the nominal resistance value. Some lots are skewed more toward high side of tolerance, others to low side. Other lots are more leptokurtic (tightly distributed) than others. On some occasions, 1% parts are binned from 5% orders, so these orders could have fairly flat or platykurtic curves. In order to guarantee a tightened matching level, simply advise your resistance matching requirements, so that RCD can quote and produce accordingly. Depending on the product, RCD can often achieve tolerance matching to 0.01% or tighter.

Unless indicated otherwise on data sheet, or specifically prearranged before ordering, there is no guaranteed TCR tracking level. Parts with an absolute TC of 10ppm therefore will track within a range of 20ppm (i.e. – 10 to +10ppm). In actuality though, if all parts are manufactured at same time under the same conditions, the TC might track much more closely. In order to guarantee a tightened tracking level, simply advise your TC tracking requirements, so that RCD quotes and produces accordingly. Depending on the product, RCD can often achieve TC tracking to 1ppm or tighter.

The level of outgassing depends on the product and loading conditions. When outgassing is a concern, we can utilize a special ceramic coating (on most products) which is supplied to a variety of aircraft and Space applications. We don't have ability to test outgassing at our lab here but have been told by customers that it is excellent (less than 1% total mass loss and less than 0.1% volatile condensable material). We can supply samples for customer verification or send to an external Materials Test Laboratory (cost to be borne by customer).

The voltage coefficient is the temporary shift in resistance due to application of voltage across a resistor; typically measured at 10% rated V & 100% rated V, after correcting for self-heating effects. This is generally caused by molecular irregularities in the resistance element. It is similar to the temperature coefficient except voltage-based instead of temperature. It doesn't relate to pulse capability (some parts with near-zero VC will shift far more and open sooner than other parts with relatively high VC's).

 

One of the main purposes for knowing the VC is to improve circuit accuracy (especially in high voltage circuits). For instance, if a part has 10ppm VC (.001%/volt) then the part will shift from its nominal value by up to 1% at 1KV. That may be fine for a 10% circuit but obviously could present a severe problem to a 0.1% circuit.

 

RCD offers a wide range of customized options via the use of specialty materials and processing to achieve improved VC stability, if the standard rating isn’t adequate.

There are three basic precision resistor technologies... wirewound, thin film, and foil. Although there are some variations, the vast majority of parts in all three technologies utilize Nickel Chromium as the resistive material. There are very few firms that produce all three technologies, so keep in mind that the info received from other manufacturers might be slanted toward their respective products.

 

The oldest of these technologies is wirewound. RCD’s President, Louis J. Arcidy, was instrumental in the development and advancement of this technology since the early 1950's. RCD was founded 4 decades ago to produce ultra-precision WW resistors, and still maintains a dominant position in this market. Wirewound resistors have traditionally been regarded as the “Cadillac” of the industry, and to this day are greatly preferred in some applications such as high-end audio and medical instrumentation. WW resistors have the greatest mass of resistance material which, with proper processing, results in highest stability, lowest noise, lowest VC, and greatest overload capability. It is this reason that nearly all Resistance Standards, i.e., those used by NIST and other Test Laboratories to calibrate precision measuring equipment, are wirewound technology.

 

Foil resistors evolved just after wirewounds and attracted a loyal customer base particularly in higher frequency applications due to low inductance and smaller PCB real estate.  Foil technology has traditionally offered performance levels approaching that of wirewounds at pricing which was typically 20% more economical. Recent advances in foil technology have resulted in temperature coefficients that are equal or better than those of wirewounds, and thermal EMF’s that are approximately equal. The best wirewound resistors are typically 0.5 to 1ppm/E TCR, whereas some foil resistors are now available as low as .25ppm/EC. Very few applications require tighter than 1ppm to 5ppm so these can typically be filled by WW or foil technology.

 

Thin film resistors have encroached upon both WW and foil technology, and are particularly cost effective in less precise applications, i.e. tolerances of 0.020% to 0.10% and temperature coefficients in the range of 5ppm or larger. The pricing advantage over WW and foil technology is especially significant in higher resistance values (i.e., 100Kohm and above). Performance levels have steadily improved and although not quite at the level of WW and foil yet, are still suitable for many precision applications, especially in environmentally controlled environments, and applications without pulses/surges.

 

Precision wirewound resistors therefore are generally the best all-around choice for precision DC and low frequency AC applications (due to inherent inductance of WW construction, they are generally not suitable for high frequency applications).  The major disadvantage of wirewound resistors (other than higher inductance level) has always been “pricing”, but with offshore production capability and advancements in automation, RCD’s wirewounds often now sell at a 20% discount to foil resistors instead of the traditional 25% premium! As a result, many customers have been switching away from film and even more so from foil technologies in favor of wirewounds over the past few years.

Yes, RCD's silicone coated wirewound resistors (such as Series 100, 200, T, and RW) are compatible with aqueous cleaning systems however the coating is designed to be softer than others to enable the resistance wire to expand and contract in use (thereby offering greater stability and higher surge capabilities). Customers should avoid any harsh brushing or high pressure on parts. The parts should also be promptly dried after washing.

schematic
 
When current terminals I1 and I2 are connected to load, the voltage flows through terminal I1, then through the current sensing resistor element, and the other current terminal (I2).  The same voltage is generated between terminal E1 and terminal E2 as well as at the both ends of the current sensing resistor. This voltage enables the detection of the flowing current.

 

Current [I] = Voltage [E] / current sensing resistance [R]

 

Though voltage generates at the terminals in a current circuit, it is not included in a voltage sensing circuit so it need not be considered. The terminal resistance (aE1 and bE2) is quite small related to impedance in a voltage sensing circuit, so it is possible to measure the current accurately without any consideration about resistance.

 

Refer to Engineering Report R-31 for additional information.

Our general rule of thumb for is to have approximately a 13mm (1/2") clearance between the body of resistor and any combustible materials. Some customers utilize much smaller clearances depending on the PCB material and the fault condition. If the only possible fault is one in which the resistor will fuse very quickly, then there shouldn't be enough time for the generated heat to transfer to PCB or nearby components. If however the fault could conceivably result in the resistor "hanging in" for seconds or minutes, then the resistor body could reach very high temps before fusing and could char or ignite the PCB or nearby components. If unable to achieve the recommended clearance, customers should evaluate prototypes under worst case conditions. Even a very small clearance such as 1mm would be far better than mounting the resistor body directly on the PCB since the air space acts as an insulator. Fuse resistor models which include a built-in thermal cutoff (such as RCD’s TF and LF Series) will not achieve the same temperature extremes and therefore can generally be mounted closer to the PCB and adjacent components.  

Power wirewound resistors are often utilized in fairly high voltage applications (pulse or continuous). Since the breakdown voltage of most models is 1000’s of volts per centimeter of length, high voltage levels can be achieved with long body lengths, particularly in applications where substantial inductance isn't a problem. If the resistor is subjected to an excessive amount of voltage or energy, the failure mode for these resistors can cause catastrophic damage to other components.


A wirewound resistor is made by winding a fine resistance wire, such as Nichrome, on a ceramic rod. If a small open develops in the winding due to excessive power/voltage/energy level, an arc will form at the gap, melting the wire back, making the arc bigger. As the process continues, the results can be rather explosive especially at high voltage levels. And since the failure mode can be a partial or full short through the resistor, it is likely that additional components in the circuit will be damaged. Never exceed the resistor’s ratings. RCD generally offers both continuous and short-term ratings (since resistors are capable of overloads for short periods). Our engineers are always available to assist in product selection. In some instances, a slightly modified design can result in a large increase in overload capability for little or no extra cost.

Composition resistors are great for applications that require special performance characteristics such as high surge energy, high peak pulse voltage, low inductance, high operating frequency, and non-magnetic construction. However in normal-use applications, they tend to be less stable than other resistor types, especially in the presence of moisture/thermal/voltage gradients.  Composition resistors are the only Mil-spec product for which an “out-of-tolerance” condition is actually expected and specifically addressed in the Military drawing (MIL-R-39008)…

 

     “6.9 Out-of-tolerance resistors. Resistance shifts due to absorption of moisture are inherent”.

 

As a result of this instability, the drawing specifies that the out of tolerance resistors be pre-conditioned in a dry oven at a temperature of 100ºC ±l5ºC for 96 ± 14 hours in order to obtain a more accurate measurement. Since composition resistors can rapidly shift out of tolerance, and since users generally don’t want to bother with the preconditioning processes, it is common to specify a tolerance tighter than actually needed (i.e. 5% tolerance if 10% is actually required, or 10% tolerance if 20% is required).

 

Composition resistors also tend to be more costly than other models, so if not needed for any of the special performance characteristics, customers should consider other models (consult RCD Engineering for application assistance).

Depending on the product, increased ratings are typically achieved via special materials and/or processing, much of which has been developed over the past 30+ years as a specialty component manufacturer. The details are proprietary but a brief description of each follows. Please note that in addition to the increased ratings that may be listed as Options on the data sheets, RCD can often achieve even higher wattage, voltage, amperage, dielectric, and overload levels (this extra level of performance can sometimes add significantly to the unit price).

 

Power: Increased power ratings are achieved primarily via use of materials with improved thermal conductivities. For instance, to improve a conventional leaded-wirewound resistor, the core, caps, leads, and coating material may all be optimized to enable a greater transfer of heat out of the resistor body into the surrounding air or through the lead wires into the PCB. Surface mount chips, such as MC2512B (2W in 1W package) and MLB2512 (3W in 1W package) also utilize such techniques as heavier/wider terminations, greater resistance layer mass/surface area, and specialized trimming to prevent hot spots and current crowding. The suggested mounting footprint is typically larger than conventional product to aid the thermal transfer. Some products also receive special processing and high-temp preconditioning to ensure stability at the elevated power levels.

 

Voltage: Increased working voltages may be achieved by utilizing special high voltage insulations and by modifying the element geometry to prevent internal arcing.

 

Amperage: Increased current ratings often involve heavier-duty terminals and internal design. This is often achieved by utilizing heavier gauge resistance wire, high thermal conductivity materials, and/or terminals with reduced resistivity and greater mass.

 

Dielectric Strength: Increased DWV (dielectric withstanding voltage) is generally achieved by utilizing materials with greater voltage capability, or by increasing the insulation thickness using standard materials.

 

Overload: RCD’s products are generally capable of brief overloads. In order to increase the power, voltage, and/or duration of the overload, RCD will often utilize a combination of special materials and processing. This may involve larger internal elements, heavier gauge resistance wire or film thickness, different resistance alloys or film compositions with higher voltage or current-carrying capabilities, higher melting points, special preconditioning, customized winding/ trimming/calibration, etc.

TEMPERATURE SENSOR FAQ

RCD’s temperature-sensitive resistors (also known as Resistance Temperature Detectors or RTD’s) function as a result of increasing resistance in proportion to increasing temperature. When a known current (generally very low to prevent self-heating) is placed through the RTD, the output voltage indicates RTD resistance.  Since the relationship between the resistance and the temperature is known, the temperature can thus be determined. For example, a resistor wound with pure platinum that measures 100 ohms at 0ºC will measure 139 ohms at 100ºC.

The level of sensitivity that a resistor has to temperature (known as the temperature coefficient or TC) is dependent upon the resistance alloy.  Platinum has the best range and is the most common metal used for precision sensors. RCD also manufacturers sensors of numerous other alloys enabling a wide selection of TCR levels. RCD has been producing RTD’s for over 30 years and has one of the industry’s widest ranges of leaded and surface mount elements, as well as a full range of probes designed for air or liquid immersion up to +640ºC.