HIGH-DENSITY SOCKETS FOR TEST & BURN-IN OF MICRO-BGAs, CHIPS and WAFERSAuthor: Gabe Cherian
Company: Cherian Enterprises
Date Published: 2/13/2001 Conference: Pan Pacific Symposium
First, the need for sockets in general.
Packages need to be tested, to sort out the marginal or defective ones, before processing them further. They undergo what is known as “test and burn-in”, to cull out those that are susceptible to “infant mortality”. In this process, packages are usually inserted into “test sockets”, which are mounted on test boards, and placed in test chambers, which “accelerate” this aging/test process. Also it is desirable to easily remove a package from an electronic system and replace it with another, without the need to de-solder and re-solder the package directly to the board. So-called “Production” sockets can be soldered onto the board and the packages can be inserted into the sockets, without another soldering operation. This reduces the chances of damaging the packages due to the second soldering operation. Sometimes, such sockets are also referred to as “connectors”.
The second factor is the need for “High Density” sockets. This is because the electronics industry keeps pushing towards “miniaturization”. Packages used to have their contact leads on 0.100” (approx. 2.540 mm) center distance or “pitch”. The pitch is being constantly reduced to smaller and smaller distance, and instead of leads, many packages now have simply “contact pads”, such as the BGA (Ball Grid Array) packages. The distance between these pads now is being reduced to 0.040” (approx. 1.016 mm), 0.025” (approx. 0.635 mm) and even 0.020” (approx. 0.508 mm) center distances. Some BGAs have hundreds or even thousands of contact pads in an area of less that one square inch. This is “high density”.
Sockets that are used with such packages need to have their contact springs, distributed in a pattern that matches the pattern of the pads of those packages. It is difficult and expensive to make contact springs small enough to fit in the available space. As a result, it is getting more difficult and more expensive to make such sockets, with such small center distances.
I have found an economical way to design and manufacture test sockets and connectors, with such small center distances, with springs that would satisfy the above requirements and the market needs. They are also relatively less expensive or at least competitive in price with most any other socket available on the market.
Similar sockets can be designed and built to work with “chips”, before assembling them in final products.
Furthermore, since many of these tests are frequently done at varying temperatures, the effects of TCE Mismatch can be detrimental. My designs take care of this problem as well.
In this paper, I will describe these novel test sockets and their novel design and contact springs. I will list the plans and steps of building such sockets and their availability to the market place.
Key words: Assembly, Ball Grid Array Packages, BGAs, Center Distance, Chips, Diagonal Arrangement, High Density, Insulated Springs, Impedance Controlled Springs, Interconnection, Matching Materials, Parallel Nesting, Packages, PCBs, Production Sockets, Scrub, Small Pitch, Small Center Distance, Sockets, Springs, Staggered, Test and Burn-in, TCE Mismatch, Test Sockets, Trouble Shooting, Thermal Coefficient of Expansion (TCE), Wipe.
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