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Subject:	Re: Operating temperature of PCB
From:	Robert Tarzwell <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Tue, 8 Jul 2003 15:16:51 -0500
Content-Type:	text/plain
Parts/Attachments:	text/plain (31 lines)

Hi guys  and the answer is yes each pass through a solder temp cycle
destoyes the board a little more. most .062 1 oz plated boards can only
withstand 2 or 3 cycles before they start to crack at the via to joint. now
as most things are cumilitive and definable it may take 4-5 to acualy open
but I have and can easly find cracks starting as low as 2 cycles. remeber
the board manufacturer takes two cycles away because he hot oil reflows and
he oven cures for solder mask. I have a chart  where I did a test of copper
thickness vers's heat cycles. 1 oz fialed in 5 to 7 cycles ( no pcb
manufatures cycles)  2 oz survived 7 to 12 3 oz 15 to 20 4 oz threough 10 oz
were not realy affected. it appears that the heaver copper vias are able to
resist the push of the expansion forces happening when you solder. the
initial question was does high temp affect a board and the answer is more
then you think. So if you want a very reliable board add extra plating, this
can be done quite easly by starting with 1/4 oz copper and use 3 or 4 mil
dry film and plate up . The etching is faster and the line definition will
be much better, but best of all your board will withstand twice the relfow
solder cycles.
Robert tarzwell   author of  high powered printed circuits and,  flex
circuit design  Megadawn.com

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