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August 2007

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Subject:
From:
"Victor G. Hernandez" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 7 Aug 2007 11:07:47 -0500
Content-Type:
text/plain
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Once upon time in the land of Big Blue the rework number for SnPb PCBA
was 3.   The 4th time it was scrap.   The HASL process was 2 times.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Tuesday, August 07, 2007 10:53 AM
To: [log in to unmask]
Subject: Re: [TN] Rework question

John,
I am having people look, but if there is a limit I do not remember.
However, from a practical point of view, the answer is Doug Pauls'
patented (Or is that copyrighted or trade marked? Being a lawyer, I
don't know.) phrase, "It all depends".  It depends on the method of
rework, (reflow, wave solder, selective soldering, soldering iron, hot
air gun focused IR, flame), temperatures reached, ramp rates, dwells,
size of board, thickness of board, type of component, heat sinks, skill
of operator. I could go on.  Make yourself a fishbone diagram.

And then are we talking about say 3X of the same component, or 5X
side-by-side or 7x but each in a thermally separated area from the other
six?

Here's a scenario for you: double sided reflow and then required rework
under cans on both sides of the board. So this means two more for can
removal, dressing the can pads, removing the components, dressing the
pads, part deposition, can replacement.  And hope everything works!

So you need visual inspection, x-ray inspection, electrical test and if
you really want to do it right, x-sectioning and a whole battery of
reliability testing.

I have seen good work and I have seen thin boards delaminated after a
single, poor attempt at rework.

Bev
RIM 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Tuesday, August 07, 2007 10:29 AM
To: [log in to unmask]
Subject: [TN] Rework question

Hi,

 

I had a question yesterday which was "has the number of re-work cycles
allowed by IPC changed for lead free?"

 

And I confess I don't know but I bet someone on this link does.

 

If you could let me know number of thermal cycles allowed and the spec
reference I would be grateful.

 

John

 

 

 

John Burke

 

(408) 515 4992

 


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