---"[log in to unmask]" <[log in to unmask]> wrote:
>
> Has anyone any experience of blisters (delamination) of solder
resist on copper
> planes at hot air solder levelling.
>
>         We have been through a range of checks and tests to find the
cause, including:-
>
> Surface conditioning before resist application.
> Water rinses on the brushing machine.
> Surface moisture.
> Predrying before exposure.
> In line  resist filter.
> Quality of electroplated copper.
> Final resist cure.
>
>         We are curtain coating liquid photoimageable solder resist.
Hasl is carried out
> at 250 deg.C dwell time is 6 seconds. The boards are allowed to cool
before post
> cleaning. There is minimal hold time between final cure and hasl. We
have been using the
> same solder resist and hasl process for years. Now we have this
problem.
>
>         Screen printing the same boards with photoimageable resist,
containing more
> epoxy, we do not get blisters.
>         Any response would be appreciated.
>
> Roger Hammond.
>
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>
From my experience, most of the resist breakdown problems are due to
improper final curing.
I suggest you to check the temperature distribution in your oven. The
min. temperature should be 145 deg C. (different LISM has different
setting). Temperature up to 165 deg C is O.K.  Air circulation should
be 10 CFM or above. The space between panels is very critical. It
should be 15 mm or higher. Do not open the oven door during the
curing. If you still have resist breakdown problem at HAL, I suggest
you pre-bake panels at 150 deg C for 10-20 min. and HAL with 10 min.

I hope it can help.


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