Rework is not included in the board calculation and design, because rework
should not be necessary if the process is well done. When the doc puts in a
new heart, he probably has the intention, that this heart will work until
the end. And the boards for pacemakers are certainly not planned for rework.
Likewise, our advanced boards are constructed for making a good job the
coming 20 years. However, the reality is different. The human factor,
modifications, missing components and a whole bunch of other reasons make it
obvious, that repair is something we can't escape from, especially as many
boards are extremely expensive. So...we have had this rule for decades:
All boards must be able to undergo 5 times of repair.
Furthermore, don't forget that even if you have repaired only twice before
shipping, your customer may do own repairs both one, two or more times. If
he can't repair your boards, he may stop buying from you.
Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Bev Christian
Skickat: den 7 augusti 2007 17:53
Till: [log in to unmask]
Ämne: 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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