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December 2006

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Subject:
From:
Roger Stoops <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Roger Stoops <[log in to unmask]>
Date:
Fri, 8 Dec 2006 17:17:33 -0500
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text/plain (114 lines)
Good points as always, we have never had any problems with silkscreen.

Good point too about servicing boards, esp. in rain (how about snowstorm?!?) when service techs may begin making rude comments about ancestry and stuff.  But this may not apply with inexpensive electronics (read, throw-away items).  Service tech years ago showed me shelves full of boards that needed servicing, but didn't get it, because they didn't have the time and the cost associated with repair (repair inside US, that is).  Guess it depends on the end product/use or POV, example: why put silk on cell phone board if likelyhood is it will be landfill in 3 years or so, and not need servicing?

Have a good weekend all!

Roger

-----Original Message-----
From: Barbara Burcham [mailto:[log in to unmask]] 
Sent: Friday, December 08, 2006 5:06 PM
To: TechNet E-Mail Forum; Roger Stoops
Subject: RE: [TN] Silkscreen Outgassing?

I worked for Halliburton Downhole Div. for years and we always applied white epoxy silkscreen to our polymide boards, over the soldermask.
I have seen these boards come back from the field and the white silkscreen sometimes looked yellowed from the temp extreme, but it never caused any outgassing problems. And if it did, it would not have damaged the assembled boards. 

I am a designer and I place all the ref. des. I can possibly squeeze onto the board. What happens in the surface mount line and production test may be blind, but the field service guys really don't want to be out in the rain, searched for R301 out of 500 resistors......
Make it easy on everyone whenever possible. What may take hours in layout, may save many many hours on down the line.

Barbara Burcham, C.I.D.
Sr. PCB Designer
RFTrax a Fairfield Co.
[log in to unmask]
281-276-5916
281-276-5950 fax
 
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roger Stoops
Sent: Friday, December 08, 2006 3:47 PM
To: [log in to unmask]
Subject: Re: [TN] Silkscreen Outgassing?

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
VP, Business Development
T: (800) 560-9457
F:  (800) 878-5566 (y servicio de mensaje espaņol)
E:  [log in to unmask]
W:_  www.CircuitConnectUSA.com_ (http://www.circuitconnectusa.com/) 



Circuit Connect, Inc.

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