Many new electronic devices, such as microprocessors, require testing at every step, from design to production. Conventional test-fixture designs often require that chip packages be soldered to adapters, which then plug into test sockets on the test fixture board. However, by adding a soldering step to the test process, this approach extends the overall test cycle time, slows throughput, requires tested chip packages to be "reballed," and introduces the risk of thermal damage to the chips.
A test-equipment manufacturer needed help in accelerating BGA-packaged chip testing without having to solder the BGA package to the adapter. We produced a custom multilayer FR-4 test fixture board that incorporates a combination of three cable-to-board connectors to interface with the test system, along with an adaptation of an existing BGA socketing system into which the packages-under-test insert.
The BGA package to be tested is simply placed on top of the modified socket, covered with a support plate, and secured by a sliding clamp and coin screw. Optimal electrical continuity is ensured by spring-loaded beryllium copper contacts loaded in pogo pin terminals, the heads of which compress against the balls of the BGA package to create a gas-tight seal.
The redesigned test-fixture board employs surface-mount technologies. Vias are used to make required trace-to-trace connections between the various board layers, and the cable-to-board connectors are surface-mounted. All soldering of the test board can be accomplished in one step. The simplified mode of board construction ensures that the boards can be produced quickly for the test-equipment manufacturer at a reduced cost.