While it is preferable to test with a switch matrix that has more pins than the device, sometimes you have to test a very high pin count device on a smaller tester. Devices with 800 to over 2,400 pins are becoming more common in certain sectors like mobile phones, high-performance processors, and programmable FPGA devices. While a chip manufacturer, or OCM, might have some limits to the packaging technologies used, a distributor using curve tracing as a counterfeit device screening tool could see a virtually unlimited range of package types.
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 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.
Partially populated universal BGA socket with alignment plates
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.
Rotate in socket
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.
2304 lead universal BGA socket on an extended 1152 pin Octapogo DUT board