I'm calling the Pillow Tag Police on Robert...
This has been an interesting topic for debaste for years, but boils down to assembler and designer prefs. Our assemblers prefer silk whenever possible for the reasons you mention. Robert has an interesting point for boards that use fully automated assembly and test, at 1,000s and 1,000s per year. If I didn't have to deal with silk on boards, design turnaround would be faster, not to mention cheaper too!
But I have never heard of or seen silkscreen outgassing, ever! Sound like pcb vendor blowing gas.., er, smoke!
Maybe issue is the temp at which the boards will operate. Is it possible the op-temp of the cured silkscreen is being reached or exceeded? Silk sees temp extremes during soldering, but rarely at any other time. Still sounds like flatulence to me...
Roger
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, December 08, 2006 4:29 PM
To: [log in to unmask]
Subject: Re: [TN] Silkscreen Outgassing?
Hi Robert!
As an assembler, it just makes a lot of things easier having silkscreen on the board if there's room. Programming changes, test trouble-shooting, documenting rework, etc.. We build many boards that don't have room for reference designators, but I always advocate silkscreen if there's room.
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Lazzara
Sent: Friday, December 08, 2006 3:22 PM
To: [log in to unmask]
Subject: Re: [TN] Silkscreen Outgassing?
I think the substrate itself is far more hygroscopic than either the mask or the lettering ink.
Unless the inks aren't fully cured.
But to your point: It's quite possible to have a polymer mask and a UV letter screen.
Or combinations including epoxy inks.
So out-gassing, if any, would not necessarily have to be the same for the solder mask as for the silk screen.
But I'm curious: Why letter screen at-all?
- Are these boards being hand assembled?
- Is the lettering functional for repair purposes?
Most of the boards we fab today are so dense you can't even see the post-assembly board. So unless you're hand-popping parts why risk ink-on-pads -- with or without out-gassing?
Think I'll go tear some tags off of pillows...
ROBERT LAZZARA
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