I agree with Werner. Bare PWBs really do not need to be baked at temperatures above 105 C in order to achieve effective moisture removal. I have only seen but one PWB whose moisture was not reduced to 20% or less of full saturation moisture content after an 8-10 hour bake at 105 C.
I performed an extensive qualification of our bake processes using many different types of board materials, copper contents, size, layers, etc, ranging up to a PWB that was 40" x 34", with 48 layers, board weight of 75 lbs. This particular board required 12 hours at 105 C, but after that the moisture content was less than 20%. Baking beyond the 20% level has little value, because for each hour of baking beyond that point the rate of moisture removal is very small.
Solderability is affected when baking, but if done properly the increase in DPMO is very little, with the possible exception of immersion tin plated PWBs which are very susceptible to oxidation.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Monday, May 04, 2009 10:03 AM
To: [log in to unmask]
Subject: Re: [TN] PCB baking
Hi Rob,
No 'baking ' benefit is likely from baking above Tg; however, I am really concerned about solderability as well as damage to the PCB resin, sitting this long above Tg with its large CTE.
Werner
-----Original Message-----
From: Rob Strecker <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, 4 May 2009 10:54 am
Subject: Re: [TN] PCB baking
I have read the same thing. 105 - 125C around 4 hours. Our PCB supplier has had
issues with the pressing time in there process and we are seeing more
delamination on our boards again. They have recommended we bake our existing
stock, 5 boards stacked in the oven, at 180C for 2 hours (including ramp). My
main concern is the solderability of the ENIG finish after this baking profile.
They have shown me some pictures after bake and the gold is darkening. They are
asking us if this is acceptable because the boards passed a solder dip test. We
are going to bake some boards ourselves, paste and reflow to see the impact.
Any thoughts on the 180C bake temp? It seem as though they want the bake
temperature above the Tg temp (170) not sure why?
Rob Strecker
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Monday, May 04, 2009 7:57 AM
To: [log in to unmask]
Subject: Re: [TN] PCB baking
Hi Ioan,
No there is not, and there really cannot be.
The temperatures used are in the range of 105 to 125-I tend towards 10
5 C, but
the duration depends on a whole lot of factors. Among them: moisture content
[bake time ranging from 0 to 24 hours plus], construction [thickness, P/G layer
location, PCB resin, resin content, PTH/via pitch/diameter], reflow
process/temperature, etc.
My recommendation is to determine it yourself on some coupons supplied with the
PCBs.
Werner
-----Original Message-----
From: Ioan Tempea <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, 4 May 2009 9:25 am
Subject: [TN] PCB baking
Dear Technos,
I know this has been oftenly discussed here, but I would like to lively up the
traffic a little bit...
Is there any IPC standard reglementing the bake out time for PCBs, in terms of
temperature/dwell time?
Thanks,
Ioan Tempea, ing.
Ingénieur Principal Fabrication / Sr. Manufacturing Engineer
30 ans déjà! - Already 30 years!
950 rue Bergar, Laval, Québec, H7L 5A1
t : 450-967-7100 ext : 244
Mtl : 514-990-5762
f : 450-967-7444
[log in to unmask] <mailto:[log in to unmask]>
www.digico.cc <http://www.digico.cc/>
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