In this product highlight we will discuss our offering of resistor chip arrays and the benefits of arrays over discrete components. We offer three different termination types. We will discuss the benefits of each type, and discuss the cost factors to consider when deciding between arrays and discrete components. Chip arrays are commonly used in very high volume, and represent an opportunity for growth. Recent improvements in volume manufacturing have improved Stackpole’s cost structure such that we are now well positioned to increase our share in the chip resistor array market.
Chip Resistor Array Advantages
The obvious advantage that chip arrays provide is integrating several resistors onto a single part. This lowers overall component count and the number of placements needed, reduces the size and weight of a design, and increases reliability. The impact of reducing the number of placements can be significant. In fact, for small size chip resistors, the placement costs far outweigh the cost of the component itself when you consider the total cost of using each component. Even though the component price of an RAVF 164D is more than the cost of four discrete 0603 chips,when you factor in the placement costs for four discrete components vs. one array, it is clear that the total cost of the array solution is lower than the discrete solution.
Beyond the benefits of reducing component count chip arrays offer improved repeatability since each resistor in a given chip array will track in terms of tolerance and TCR. This is due to them all being the same resistor ink, on the same substrate, fired on at the same time, and most likely all having the same laser trim length. For example, a 1% and 100 ppm chip array will have its individual resistors track to within 0.5% tolerance and 50 ppm TCR and in most cases will be even better than that. This dramatic improvement is enough in many cases to allow the customer to continue to use 1% tolerances when they would have been forced to move to 0.5% tolerance parts which are much more expensive and are more limited in their availability from stock.
Applications for chip resistor arrays vary almost as widely as those for standard thick film chip resistors. Additionally chip arrays are a popular choice for pull up and pull down for logic gates, communication data lines, and current limiting resistors for memory modules. They are regularly used in many types of computers and computer peripherals, network communications such as servers as well as portable testers and network analyzers.
Convex Terminations – RAVF Series
This is the most common of all the termination types with the most options and where most new product development efforts are being focused. We offer 0402 x 2, 0402 x 4, 0603 x 2, 0603 x 4, 0603 x 8, and 1206 x 4 packages. The RAVF 164D is an 0603 x 4 and is the most specified chip array for Stackpole. It also provides the lowest overall cost per resistor among all chip array termination types and sizes. If there is one product to remember out of this pitch pack, it would be the RAVF 164D. Contact us for the new book pricing for the RAV 164D 5%.
Advantages of the convex termination style include lowest cost, highest volume and best stock availability. Additionally, solder joint verification equipment can treat the convex termination like any other discrete termination, which simplifies their usage in mass production. The only disadvantage to the convex termination in the past was that the corner terminations were wider than the interior terminations as shown above. This meant the part wasn’t interchangeable with concave termination array types. Stackpole has now adjusted the edge terminations to be the same dimension as all the others for the most popular combinations 0603 by 4 and 0402 by 4.
Concave Terminations – RACF Series
The next most common termination type is concave. This was the first termination type offered in a chip array form, so there is significant print position for this type. The most popular part for this series is the RACF 164D, for similar reasons as the RAVF. The RACF is offered in 0603 x 4, 1206 x 4, 0603 x 8, and 1206 x 8. Book pricing for the RACF 164D 5% has recently been reduced, contact us for current book pricing.
The only advantage of the concave termination type in the past was that it has completely symmetrical terminations which simplifies board layout; as discussed above this is no longer a significant advantage. The disadvantages are that the terminations are in somewhat of a valley, making solder joint verification difficult. Concave termination types are also limited in how small they can be made since the corners of this termination type are much smaller and are susceptible to breaking off. Because of this, most of the development for smaller sizes and higher integration are being done in the RAVF or RAF series.
Flat Terminations – RAF Series
As chip array sizes get smaller it becomes increasingly difficult to achieve the scalloped areas seen on the previous two series, making the ceramic substrate significantly more expensive. For those smaller sizes it in fact makes more sense to simply eliminate the scallops entirely. It is now widely accepted across the electronics industry that those areas don’t significantly deter solder bridging; many different types of SMD components are now soldered with the same pitch as seen on these small chip arrays. This changes the cost of the ceramic substrate from extremely expensive, to very inexpensive.
Special Chip Arrays – RAVN Precision Thin Film Chip Array and RAVS Anti-sulfur Thick Film Chip Array
Stackpole also has some specialty chip arrays which should be noted. The RAVN is a thin film chip array designed for applications requiring high precision. It is available in the most popular size 0603 by 4 in tolerances down to 0.1% and TCR as low as 25 ppm. The RAVS is an anti-sulfur chip resistor array series. Thick film resistors in the presence of high concentrations of sulfur are susceptible to contamination which causes resistors to increase in value until they ultimately open completely. The RAVS reduces the amount of silver, which is the material in the termination that is susceptible to sulfur contamination resulting in a part which is far more robust. The RAVS is available in the popular sizes 0402 by 4, 0603 by 4, and 1206 by 4 in tolerances as low as 1% and in a wide range of resistance values.
Data Sheets for these series are available at: www.seielect.com.
For more information about Stackpole products, contact Stackpole Electronics, Inc. at
Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now part of the Akahane Stackpole Manufacturing Group (ASMG), Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Shenzhen and Japan; and international sales offices in Tokyo, Taipei, London, Hong Kong and Shenzhen.