Roger -
What is the lead frame material? Just a guess, but I would be willing to
bet it is Invar or Alloy 42 and the solderability is degraded due to
age.
Jeffrey A McGlaughlin, CID
Engineering Designer
Battelle Memorial Institute
Columbus Ohio
http://www.battelle.org
[log in to unmask]
-----Original Message-----
From: Roger Stoops [mailto:[log in to unmask]]
Sent: Thursday, January 06, 2005 3:12 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Joint Failures after Short-term Vibration
Ah, now this is something to think about...
The grainy appearance of the leads is the first thing that drew my
attention. However, these same parts are used on other assemblies with
no apparent problems (but I will ask about potential lead
plating/contamination problems).
And
1) There are micro-voids in the solder joints. According to 610C, up to
25% voiding of BGA ball to board interface is process indicator but can
be accepted. But our vendor is telling us they are passing anything
under 50% (minus any area of lead not on land) total area , per 610C
section 12.2.5.3 (pg. 12-45). Anyone know or have experience with how
this relates to non-BGA joints?
2) Pads are about a mil [.025mm] wider than lead. (Never been a problem
before, but...)
And we are not seeing full height toe fillets; in fact, some toe fillets
are less than 50% of the lead height.
Roger
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Paul Edwards
Sent: Thursday, January 06, 2005 2:49 PM
To: [log in to unmask]
Subject: Re: [TN] Solder Joint Failures after Short-term Vibration
Roger,
It almost sounds like you have a QFP lead plating problem....
The EMS is probably right and these meet the spec...
However for your application IPC is not enough...
The reason the top of the lead is grainy is because that is the reflowed
condition of the QFP plating...
I would guess that
1) If x-rayed you have micro-voids in the solder under the leads
2) Your pads are the same width as the leads on the QFPs for the failing
lot
You need to get full height toe fillets on the QFP leads...otherwise
they
will fail...
It is possible to do but requires secondary operations...
Paul
Paul Edwards
Process Engineering
[log in to unmask]
Tel: 408-433-4700
FAX: 408-433-9988
Surface Art Engineering
81Bonaventura Dr.
San Jose, CA 95134
DUNS: 944740570
CAGE/NCAGE: 1XZ48
-----Original Message-----
From: Roger Stoops [mailto:[log in to unmask]]
Sent: Thursday, January 06, 2005 10:19 AM
To: [log in to unmask]
Subject: [TN] Solder Joint Failures after Short-term Vibration
Hello all,
We are having an ongoing problem with solder joint failures on a 144-pin
PQFP processor, after short-term vibration. The board layout and
mechanical
mounting apparatus were designed with vibration in mind, and have passed
vibration testing in the past. The same processor is used on a dozen
other
assemblies, none of which have this problem.
The solder joints appear to exhibit dewetting, although there is a toe
and
heel fillet. The heel fillet is unusually large, and the top of the
PQFP
lead has a grainy appearance instead of a matte or shiny appearance.
Some
leads can be pushed off the solder joint with very little pressure.
Sn62Pb36Ag2 solder is being used, and our EMS provider continues to
claim
that boards meet IPC-A-610 class 2 requirements.
Any ideas as to what may be causing solder joint failures?
Also, any suggestions or recommendations (preferred) for a test house to
provide x-ray, microsection and composition analysis?
TIA & Best Regards,
Roger M. Stoops, CID+
Trimble Navigation Ltd., Dayton, OH, USA
Ph: +01 937.245.5288
Fax: +01 937.233.7511
Oh, and BTW, changing EMS providers is not an option...
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