Just curious Mike,
how do you test them for multiple times? And how do you design (materials,
process) for multiple pass resiliance? And if they don't pass, what do you
do?
Thanks,
Ioan
> -----Original Message-----
> From: Mcmaster, Michael [SMTP:[log in to unmask]]
> Sent: Thursday, July 10, 2003 2:19 PM
> To: [log in to unmask]
> Subject: Re: [TN] Operating temperature of PCB
>
> We are finding more and more customer's specifying PWB thermal stress
> testing at multiple times (up to 6) at 500F (260C) rather than 1x550F
> (288C).
>
> Mike McMaster
> RF Product Engineer
> Merix Corporation
> 503-992-4263
>
>
>
> ----------
> From: joyce[SMTP:[log in to unmask]]
> Reply To: [log in to unmask]
> Sent: Wednesday, July 09, 2003 4:45 AM
> To: [log in to unmask]
> Subject: Re: [TN] Operating temperature of PCB
>
> Not if you qualify your vendor properly. Four reflow normally should be
> used for qualification.... Or 3 reflow plus one wave.... Depend upon it
> is mixed or not.... (At user's location, not include HASL, plating
> reflow at vendor site...). Find open via at assembly is non-starters
> (you pay 10x more than qual the board house...).
> Poor ($) fellow's take on this...
> jk
>
> >-----Original Message-----
> >From: TechNet [ <mailto:[log in to unmask]>] On Behalf Of
> >Robert Tarzwell
> >Sent: Tuesday, July 08, 2003 4:17 PM
> >To: [log in to unmask]
> >Subject: Re: [TN] Operating temperature of PCB
> >
> >
> >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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