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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