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May 2006

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 30 May 2006 10:13:42 -0500
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Susan, in your expert opinion, will passing this float method test
preclude delamination and z-axis expansion leading to via cracking in a
standard 63/37 SMT oven reflow process? What about for a 250 C Pb-free
reflow process or condensation reflow process?
The reason I ask this question is because many BGAs now come only with
lead free solder spheres, but they are soldered using tacky flux (no
solder paste) in a slightly elevated temperature profile (TALT = ~230C
for 60 sec) along with all of the other standard 63/37 components. Also,
many CMs and OEMs are going back to using condensation reflow to get
more uniform heating for a lead-free process. Is the float test good
enough to qualify the pwb to withstand these assembly processes?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Susan Mansilla
Sent: Tuesday, May 30, 2006 7:16 AM
To: [log in to unmask]
Subject: [TN] Dip or Float

Thanks for confirming what you are actually doing in this test.  We have
come up against the two different styles and have had trouble
correlating results.
 By dipping the process simulates a Hot Air Solder Leveling process.
All of the stresses are equal since both "sides" of the board see the
same heat at the same time.  The float has a really hot bottom and a
relatively cool top.
This allows (causes) z-axis expansion that weeds out both barrel cracks
and inner layer separations.

There are no IPC test methods that call for dipping other than the
solderability tests.

Thanks again for the clarification

Susan

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