Thermal Analysis and desired/required design margin should be able to tell
you what is acceptable. In the absense of that (although not a good plan) I
wouldn't accept anything less than 75% and it may require special processing
to acheive that with good yields.

Regards,
Bruce Misner

-----Original Message-----
From: Victor G. Hernandez [mailto:[log in to unmask]]
Sent: Wednesday, June 30, 2004 2:11 PM
To: [log in to unmask]
Subject: [TN] Power FETS, Surface Mounted
Importance: High


Fellow TechNetters:

    What is a rule of thumb for Thermal Heat Sink Spreader solder fillet
coverage.   During x-ray imaging I have observed varying coverage with
respect to the PCB copper
pad foot print and the heat sink.   This ranges from 30 to 90% coverage.
I am unable to state the associated thickness of this coverage except
for gray scale keeping all setting alike.   IPC does have a guideline
for PTH Vertical fill of 50% for Powers and 75% for signals.

   Can anyone share their experience with me.

Victor,

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