Gentlemen,
thank you for the fast response.
Clarifications:
* I am talking about delamination blisters. The board looks like the surface of the outer layers is about 30% detached from the others and only the vias are holding them together. Of course, there are several independent blisters, not only one that big.
* the profile is having a short (20 sec) soak at about 170C. I actually need to soak it more, to lower the temp delta between the transformer and the rest of the comps
* I did not check what the Td is, but how will it impact delamination? Prepreg burning off and detaching?
Regards,
Ioan
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Tempea, Ioan
> Sent: Thursday, August 25, 2005 10:19 AM
> To: [log in to unmask]
> Subject: [TN] Blistering of PCB at lead-free temperatures
>
>
> Hi Technos,
>
> wanted to start a pilot run, but the first PCB that we soldered ended up full of blisters when it came out of the oven. It is a 6 layers, full ground and power planes, about 6"x7", not a high density one, pretty light stuff on it, the toughest part is a transformer which needs a little more heating. The profile peaks at 250C on the PCB itself and the PCB is made out of FR4, Tg 170.
>
> I said to myself that it must be humidity, so I baked 1 board, 8H @ 125C, and passed it through the reflow again. Same blistering, almost to the same extent. Then I took a totally different PCB that was hanging around on my desk for about 3 months, reflowed it at 250C and got just a tiny blister, probably due to humidity this time.
>
> The questions I have are:
>
> is 250C too much for a properly manufactured PCB?
>
> If it's not the humidity what else could it be?
>
> Any other test that I could do to get a better idea of the root cause?
>
> Thanks,
> Ioan
>
>
>
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