Wayne,
   I always felt that SM was a moisture barrier rather than an insulator.   My concern is if SM has Assembly Process anomalies the underlying copper can be attacked by HARSH environments, LA and India, China ""SMOG"".   Polyimide "coverlay",  you mean conformal coating!!
Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Friday, February 28, 2014 7:31 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Solder mask thickness

Hi Victor-

As long as solder doesn't wet to the conductor, it is considered masked.  I can't count the number of times "solder mask" has been confused with "insulator"!  Did it myself a couple of times until I got caught and then realized it was only a mask.  If you need guaranteed thickness without pinholes on an outer layer, use polyimide "coverlay".

On the other side of thickness control, I've seen lumps which prevented stencil gasketing.

I believe IPC advises on chemistry/compatibility issues of mask, as well as incomplete masks which don't do an effective job of masking solder, but not thickness.

Wayne

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Friday, February 28, 2014 8:07 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [TN] Solder mask thickness

Fellow TechNetters:

   What are some bench mark thicknesses for solder mask coverage over external conductors/signals.   I have not seen an actual value in any of the IPC STD that I have read, IPC-2222, IPC-6012, IPC-SM-840.   I believe that that are three different manufacturers.

Victor,


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