It depends on whether it is actually being used for thermal transfer or
electrical grounding. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Tuesday, July 22, 2008 2:12 AM
To: [log in to unmask]
Subject: Re: [TN] Solder balls

Picking up on John's point when you have sorted out (or decided to
ignore) the solder balls, your thermal pad is only soldered over about
33% of its area. Many of these devices recommend a minimum of 50%. To me
that would be a more serious problem.
Rex


Rex Waygood
Technical Manager
 
PartnerTech Poole Ltd
Benson Road
Poole
Dorset BH17 0RY
United Kingdom
 
Tel: +44 (0)1202 674333
Fax: +44 (0)1202 678028
DDI: +44 (0)1202 338222
Mob: +44 (0)7887 997403
 
[log in to unmask]
www.PartnerTech.co.uk

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: 21 July 2008 21:10
To: [log in to unmask]
Subject: Re: [TN] Solder balls

Genny,

Looks to me that the via holes for the thermal management have sucked
all of the solder from under the QFN leaving at best 50% of the thermal
pad cross section connected? - this could be an issue. However - back to
the solder balls.

I have noticed a couple of things about this assembly. The first and
most obvious is of course the solder ball issue. More telling is
actually the extent of the voiding in the joints, together thet might be
pointing to a profiling issue?

I also noticed that there is very little solder build up on what would
be a toe fillet in a QFP on the right and top side of the package (I
also notice also that the two outside joints at the top are showing
heavy metal loading at the toe , as well as the top and bottom joints on
the right side - although less so - is this a touch up with a soldering
iron?) this leads me to suspect that the QFN is probably not co-planar
with the board but has the top right corner raised somewhat from the
board, so the package may have had some rocking movement while being
reflowed as the solder melted and moved around?

Just my thoughts, fortunately you are able to actually look at it!!

John

 
 
John Burke
 
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Monday, July 21, 2008 11:56 AM
To: [log in to unmask]
Subject: Re: [TN] Solder balls

The solder balls are near the arrows.  Faint grey round objects.
This device does have a heat slug, and there are plated thru holes under
it for heat transfer.

And yes, our X-ray does allow oblique viewing.  What are you suggesting
we look for?  



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