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Subject:	Re: Using HASL finish with BGA's
From:	"Alderete, Michael" <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Fri, 3 Mar 2000 05:41:02 -0800
Content-Type:	text/plain
Parts/Attachments:	text/plain (59 lines)

Dave-

Haven't used them yet, but a BGA is probably more forgiving of
not-quite-coplanar HASL pads than are PQFPs with, say, 0.5mm or 0.4mm pitch
leads.

In a typical setup, at the time of reflow, the HASL goes molten, the BGA
ball melts, and the solder paste built up over the HASL'ed pads  goes
molten. Ball coplananrity prior to reflow, and after part placement,
hopefully had every BGA sphere either a) in contact with the unreflowed
paste or, b) better yet, partially submerged in the unreflowed paste.

In this scenario, nominal geometry solder joints will fully bridge the PWB
pad to BGA substrate pad gap, and only grossly undersized [lower volume] or
inadvertently squished BGA balls will lead to open circuits.

I suspect that BGA sphere coplanarity is a bigger concern with larger area
BGA's, especially with relatively long [greater than 1  1/4 inches] PBGA
MCMs. Warped BGA substrates, combined with highly uncoplanar HASL pads, and
a warped PWB, will probably lead to open circuit conditions.

Hope this works out for you.

-----Original Message-----
From: Dave Simmons [mailto:[log in to unmask]]
Sent: Thursday, March 02, 2000 5:46 PM
Subject: Using HASL finish with BGA's


Hi everyone,

We are currently trialing placement of some BGA's. The BGA's we are
placing are
0.8mm pitch. We have placed some on HASL boards with good results. There

seems to be a lot of talk regarding co-planarity problems using HASL. I
was
wondering if anyone uses HASL with BGA's and if so, do they get any
defects
related to the surface finish.

Thanks in advance

David

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