There are several applicable approaches to reducing pin count at the fixture level to allow a device to be testable. Each has pros and cons and varying cost, complexity, and test coverage. Over the next few months, we will explore three different techniques that may help keep your test program operational while you plan your next system upgrade. This entry focuses on the DUT’s loading process and a “rotate-in-socket” solution.
Focusing on BGA, LGA, and CSP devices also known as array packages, there is hope to reduce the total fixturing requirement through Universal Sockets. Indeed, RTI offers Universal BGA and CSP sockets where the user can reconfigure the socket for other devices with the same ball pitch. Many users don’t realize that this concept can be extended to permit testing very high pin count devices without much increase in cost over the basic fixture.
In this type of fixture, the universal socket is partially populated with pins that can contact and test the device. It also has a “clearance area” beside this array to allow for larger devices to be placed in the socket with room for the excess BGA balls to clear the socket but not contact any pogo pins. These excess BGA balls are not testable in this “clearance” area”. Rotate comes into play when the user removes the BGA from the socket and rotates it 90 or 180 degrees to allow testing another section of the device.
For example, consider a user who has a 1,152 pin MultiTrace Fixture or MegaTrace test system. That person can acquire a Univeral BGA socket with a 34×34 pin array and test any device that size or smaller. However, by drilling the universal test socket for a 48×48 array, a large 2304-pin device can now be aligned and seated in multiple orientations to be tested in 2 or more passes.