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.

Rotate in socket partial populated universal BGA socket

Partially populated universal BGA socket with alignment plates

Rotate-in-Socket Fixtures

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

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

2304 lead universal BGA socket on an extended 1152 pin Octapogo DUT board

Pros

 

  • Economical, balance test needs with the cost of test resources to best fit your budget and test requirements.
  • Lower total kit cost over a larger family of devices. If you test a lot of BGA and limited different pitches, this method is a good fit. Additional devices only have the cost of an alignment plate and lid.
  • All pins grounded unpowered curve trace is generally possible on any device that fits.
  • Scalable over a wide range of device sizes and array shapes; RTI can customize any of our BGA sockets with this type of feature
  • Use DUT boards designed for standard universal sockets, RTI has PGA and Octopogo versions available for most common pitches without additional NRE.
  • Ultimately most flexible for BGA continuity test, will work with a wide range of pin count and package dimensions.