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TAP TIMES -6- OCTOBER 2022
High-power socket designp (from 4) through each functional pin on the pack
age. Parallel pins help, but over the life
of the test, the highest load will be borne
Figure 4 below shows the current curves by a single pin, and it will degrade more
for various duty cycles. In this case a 1% quickly than the other pins while the de-
duty cycle equates to an active current vice continues to function.
dwell time of 3msec
Ultimately the highest current load probe
will fail as the contact resistance increases
dramatically compared to other pins on
the bus.
Add internal heatsink
One approach is to add an internal heat
sink to the probe array. This increases
the thermal mass and helps shed the heat (
generated at the probes contact surfaces.
This is application-specifi c so understand-
ing the device pin out is critical to success-
fully building a per pin heat sink.
Example heat sink might be to place a
This probe has a 450 msec thermal time copper sleeve over the pin groups on the
constant. Shortening the current pulses Vin and Vout pins embedded in the socket
increases the probe capability since the body.
time it takes to heat the probe is propor-
tional to the thermal mass of the probe. A three-piece probe where the center bar-
rel is fi xed in place will shed heat to the
Adding thermal mass to the probe copper slug. Adding the heatsink to the
If the thermal mass of the probe can be next page
increased along with limiting the high cur-
rent state in the test program much higher
test currents can be reached.
One way to increase the thermal mass is
to use parallel pins on the device pads. In
our example program, there are 4 pins on
VIN and 8 pins on the VoutSW pin bus.
Parallel pins
Unfortunately, parallel pins do not guaran-
tee that the current path will have equal
currents. Package proximity to the device
circuits on the die and variance in contact
resistance across the bus will cause signifi -
cant variance in the current load demands Adding the heat sink to the QFN probe increrased the thermal
time constant.
