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Subject:	Re: PCB PACKAGING MATERIAL & Baking Question
From:	"Stadem, Richard D." <[log in to unmask]>
Reply To:	TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:	Tue, 27 Mar 2007 06:43:10 -0500
Content-Type:	text/plain
Parts/Attachments:	text/plain (34 lines)

Scott,
Just a little confused here. If you are considering pre-baking your PWB to drive out moisture prior to print, assembly, and reflow, and you are concerned about IMF layer growth, well, what IMF layer growth? You haven't even formed any solder joints yet.
Pre-baking is a good idea. On ENIG boards, there are very little solderability impacts. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Tuesday, March 27, 2007 6:33 AM
To: [log in to unmask]
Subject: Re: [TN] PCB PACKAGING MATERIAL & Baking Question

Hi Scott,
I would recommend moisture bake-out prior to LF-soldering for all PCBs, since the vapor pressure in the PCBs is double than what it would be for SnPb-soldering.
You also say: "My understanding baking boards also have risk and can cause the intermetallic layer to increase with ENIG boards.  I've read this in several white papers and in seminars I've attended."
The IMC layer growth concern is a 'red herring' that every so often gets mentioned as an aside or by people who do not know what they are taking about. 
That has been the case with soldering to Cu where the Cu dissolution rate is 50-times faster than is Ni-IMC layer thickness for ENIG is not a concern you need to have.

Werner

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