Hello Martin.  You seem to imply the solder mask over bare copper.  Is this
correct?  If yes then I believe you need to investigate the adhesion of the
solder mask to the copper traces.  Perhaps contaminated copper existed which
prevented the proper adhesion of the solder mask to the trace.  It seems
from your statement that the solder mask is adhering properly to the
laminate material which would lead one to believe that the mask is OK.

The other scenario would be if the solder mask is over traces which are Hot
Air level or tin/lead electroplated.  If this is the case, then the problem
lies with the solder reflowing beneath the solder mask and allowing it to
flake off.
As solder reflows it expands, thereby creating tremendous pressures beneath
the solder mask.  If the solder mask is thin, then it will be the weakest
link in the system and will most likely flake off the traces.  Additionaly,
solder mask does not adhere to any fused tin/lead surfaces so that would
also increase the possibility of solder mask peeling.


Hope this helps.

Good luck.

Leo Lambert
At 02:02 PM 8/31/96 GMT, Martin Dooner * wrote:
>
>
>
>We are experiencing a problem with a soldermask on a a PCB during wave   
>soldering.
>The mask tends to degrade during wave soldering and remove after   
>cleaning.
>This defect is only seen over thin copper traces (especially around vias)   
>and not over
>the bare PCB.
>
>Can anyone tell me what is the typical temperatures a solder mask can   
>withstand
>during the wave soldering process (e.g. preheats, max. temp and time   
>etc.)
>
>Also is anyone else having this problem or can the flux or the cleaning   
>process be
>causing this problem.
>
>Thanks in advance
>
>Martin Dooner
>AMT Ireland
>University of Limerick
>Plassey
>Limerick
>[log in to unmask]
>
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