After reading the literature, it is more than cleaning you need to
worry about. Flux entrapment may be an issue, but I note that they did
not include any test data for thermal cycling, only stress testing. No
mention on cleaning under the component either. They did note that air
trapped under the part from the conformal coating up to and around the
part caused cracked solder joints from thermal expansion of the trapped
air. They also noted that they saw solder balls trapped under the part.
The pad sizes they recommend match the terminations, but there is no
mention of aperture reduction, which is certainly a very critical
parameter on this type of component to prevent solder ball formation. I
would qualify this component very carefully before I put it out into
production, including thermal cycling followed by microsections, full
X-ray for solder balls and joint shape/formation, thermal heatsinking,
etc. You will probably need to get down to a 50%-60% aperture reduction
to eliminate the solder balls that are sure to form under this part if
too much paste is used. Having an integral standoff should help.
I am not saying don't use this part, I am just saying there are
potentially many issues, so you should fully qualify the component. IRF
may have tested this part very comprehensively, but don't assume
anything.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: Monday, November 03, 2008 7:39 AM
To: [log in to unmask]
Subject: [TN] Intl Rectifier Direct FET

Is anyone out there using these?  While attractive from a design and
performance standpoint, it seems like it would be a cleaning nightmare
whether using water soluble or RMA.

 

http://www.irf.com/technical-info/appnotes/an-1035.pdf

 

http://www.irf.com/technical-info/appnotes/an-1050.pdf

 

 

 

Kevin Glidden

Manufacturing Engineer

Luminescent Systems Inc.


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