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Subject:	Re: Soldering fillet
From:	[log in to unmask]
Reply To:	TechNet E-Mail Forum.
Date:	Wed, 3 Mar 1999 19:08:29 -0600
Content-Type:	text/plain
Parts/Attachments:	text/plain (34 lines)

Folks,

Clarification is needed, but this comes as using 0402 under device pad to pad spacing (again IPC at
.016" versus .024") with modified 0603 pads reduced (with near 0402 device/pad relationships) to
allow relatively small fillets (to withstand thermal shock and stress during and after assembly) as
compared with those recommended. Again, not currently finding a better way (equipment or process to
place an 8 to 10 mil dot without impenging on pads), bottom side glue attachment, when needed,
necessitates using conventional pad spacing especially as spacing/tolerance relationships dictates.

All this reminds me of the LCCC days and how we all tweaked castellation to pad relationships in
hopes of not having to design in extreme measures (then). They were, of course, constraining,
tailoring, and compliant cores or surface features.

It's not my data, and I am not allowed to quote it all (there's no big secret here as Werner and
others attest) precisely. However, the results are objectively positive with high reliability joints
and no device cracking during HALT/HAST and operation. Another thing most all of us probably agree
on is carefully controlling preheat/top side board temps while taking wave temps down to near, or
in, the 470 range while adjusting conveyor speeds to ensure the foregoing and adequate wave contact
times.

Earl Moon

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