I have a 15x15 PGA module that will be tested on an ICT test station.
Basic construction of the module: Pins loaded into a plastic substrate
and that assembly is reflowed to a PCB with BGA technology. Some of the
pins are not loaded in the assembly leaving  holes in the substrate. A
test pad is placed behind the hole on the PCB.

A ZIF socket is used on the ICT test fixture to insert the module. Where
test points are needed, pins have been removed from the ZIF socket and
pogo test probes put in their place. As the module is inserted into the
socket, the pogo pins are compressed by the operator, then the operator
uses the lever on the socket to clamp all of the PGA pins. The result is
that the module has a upward force applied to the PCB by the pogo pins
and the counter force are the pins held in position by the ZIF socket.
This places the BGA connections between the PCB and the PGA pins in
tensile mode.

Now lets get down to some numbers. With 4 oz test probes and 12 test
points, the upward force is on the order of 48 oz. There are 180 pins
loaded in the PGA so that yields an average force of 0.27 oz/pin or BGA
connection. However, the force is not evenly distributed across the
module so localized forces on a given pin may be higher. A typical
example may be 8 pins immediately surrounding a test probe. That  yields
a localized force of 0.5 oz/pin or BGA connection. This may not be worse
case, but lets use this as a reference point.

Assuming a tensile force of 0.5 oz on a BGA connection does anyone see
that as a problem with the testing process creating reliability failures
in the BGA connection.

Does anyone have tensile strength data on a BGA connection? I don't have
the exact number, but I assume the BGA ball is in the 25-35 mil diameter
range.
Jim
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