Homebrew PCBs

Does anyone know what they use on PCB's to give that green coating 
that they then apply silkscreening to? Can this be purchased? IF so 
where? What are the benefits to using this?

The green coating is a solder mask.  It comes in a variety of flavors silkscreen applied epoxy, photo imaged epoxy (CIBA IIRC), and photo imaged acrylic (DuPont Vacrel).  Stay away from the Vacrel if you're going to wave solder it - it solder balls like no tomorrow.  I have no idea how you would apply these materials without professional production equipment.

  ----- Original Message ----- 
  From: Bob Weiss 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Monday, October 18, 2004 6:36 PM
  Subject: [Homebrew_PCBs] Green coating used on PCB's



  Does anyone know what they use on PCB's to give that green coating 
  that they then apply silkscreening to? Can this be purchased? IF so 
  where? What are the benefits to using this?





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[Non-text portions of this message have been removed]

On Mon, 18 Oct 2004 18:41:57 -0400, Earl T. Hackett, Jr.  
<hacketet@...> wrote:

>
> The green coating is a solder mask.  It comes in a variety of flavors  
> silkscreen applied epoxy, photo imaged epoxy (CIBA IIRC), and photo  
> imaged acrylic (DuPont Vacrel).  Stay away from the Vacrel if you're  
> going to wave solder it - it solder balls like no tomorrow.  I have no  
> idea how you would apply these materials without professional production  
> equipment.

there is some photo-imaged laminate-on film i gathered. could be bungard,  
not sure.
By the way, green 's out, red 's in now.

ST

Bob Weiss wrote:

> 
> Does anyone know what they use on PCB's to give that green coating 
> that they then apply silkscreening to? Can this be purchased? IF so 
> where? What are the benefits to using this?
> 
> 

Google: "soldermask"

http://www.rockwellcollins.com/about/additionalproducts/collinsprintedcircuits/page1823.html

Normally applied as a film and exposed/developed much like etch resists 
except this stuff never comes off. Older methods would silk screen 
soldermasks, newer methods use Inkjet technology to print directly.

Thanks for the answers...I thought it was something you could do at 
home but I guess not. What does one use to protect the copper when 
your finished with the board? Tinning?



--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell 
<a_seychell@y...> wrote:
> Bob Weiss wrote:
> 
> > 
> > Does anyone know what they use on PCB's to give that green 
coating 
> > that they then apply silkscreening to? Can this be purchased? IF 
so 
> > where? What are the benefits to using this?
> > 
> > 
> 
> Google: "soldermask"
> 
> 
http://www.rockwellcollins.com/about/additionalproducts/collinsprinte
dcircuits/page1823.html
> 
> Normally applied as a film and exposed/developed much like etch 
resists 
> except this stuff never comes off. Older methods would silk screen 
> soldermasks, newer methods use Inkjet technology to print directly.

Most boards are finished with a solder coating to protect the copper from oxidation.  This could be plated and then reflowed or by hot air leveling.  I always preferred the hot air leveling method.  The board was dipped in a flux and then immersed in molten solder for a second or so.  As it was removed from the solder, hot air jets blew the excess solder back into the molten bath.  It had several advantages over the plating method.  The alloy content was assured to be eutetic and there was little chance of having so much solder that the solder mask would chip off during wave soldering.

For home brew applications the best bet for protecting the circuitry is to use a conformal coating applied after the board is assembled.  Most of these products can be applied as a spray coat after protecting any DIP switches and contact areas with a masking tape.

  ----- Original Message ----- 
  From: Bob Weiss 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Monday, October 18, 2004 7:16 PM
  Subject: [Homebrew_PCBs] Re: Green coating used on PCB's



  Thanks for the answers...I thought it was something you could do at 
  home but I guess not. What does one use to protect the copper when 
  your finished with the board? Tinning?



  --- In Homebrew_PCBs@yahoogroups.com, Adam Seychell 
  <a_seychell@y...> wrote:
  > Bob Weiss wrote:
  > 
  > > 
  > > Does anyone know what they use on PCB's to give that green 
  coating 
  > > that they then apply silkscreening to? Can this be purchased? IF 
  so 
  > > where? What are the benefits to using this?
  > > 
  > > 
  > 
  > Google: "soldermask"
  > 
  > 
  http://www.rockwellcollins.com/about/additionalproducts/collinsprinte
  dcircuits/page1823.html
  > 
  > Normally applied as a film and exposed/developed much like etch 
  resists 
  > except this stuff never comes off. Older methods would silk screen 
  > soldermasks, newer methods use Inkjet technology to print directly.





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[Non-text portions of this message have been removed]

In a message dated 10/18/2004 6:17:55 PM Central Standard Time,  
BWeiss@... writes:

What  does one use to protect the copper when your finished with the board?  
Tinning?




BW:  Yes, the bare copper SHOULD be at least tinned, except for  "throw-away, 
one-each" hobby-PC work that doesn't have to last.  A firm I  THINK I read is 
no longer with us, Kepro, sold a "Tinnit" solid which, when  dissolved in hot 
water, would "electrolessly" tin all the bare copper that came  into contact 
with it.  I used this religiously for a time until TWO  things:  First, the 
stuff just plain "went bad" (which I learned later it  DOES), and then, I 
couldn't get in touch with that firm any longer, and seems I  READ (here?) that 
Kepro was either out of business, or had at least ceased  selling to "home shop 
folks".  
 
What I always do when doing an "important" board is solder nicely, then  
using either Acetone or lacquer thinner and an old toothbrush (using the one you  
actually still use is not tasty!) and "scrub off" all the solder-flux ("rosin  
core") melted all over the board.  Be very careful not to let that  goop run 
into IC sockets, etc.!   Hold the board essentially  vertically over a metal 
pan large enough to catch drippings, and give you also a  place to dip/re-wet 
your brush.  I do this "solvent brushing" ONLY on the  "solder side"!  If there 
are nasty spots on the top (where you soldered a  "through-hole" 
resistor-lead, etc.) I use a tiny piece of paper napkin and  swab-off that tiny spot of 
nasty on top, here and there, being super  careful not to use so much that it 
runs all over, into sockets and  non-hermetically-sealed components, etc. 
 
Then I "mask off" all the IC-sockets, trim-pots, later-to-be-soldered pins,  
etc., and then clear-spray the board, both sides, parts and all.  Then  
carefully remove all that masking tape, and use a fresh piece of it to "pull  off" 
any nasties that peeled off onto the board as you removed the  masking.  This 
keeps the nasty atmosphere off the "shiny metal", but, as  you had so carefully 
masked the sockets, etc., you can still plug in IC's,  certain of good 
contact.  
 
Takes some patience and experience.  Did I say patience?  
 
Lotsa  luck!                Jan  Rowland


[Non-text portions of this message have been removed]

> A firm I  THINK I read is 
> no longer with us, Kepro, sold a "Tinnit" solid which, when  
dissolved in hot 

> Kepro was either out of business, or had at least ceased  selling 
to "home shop 


Look in the Links section under Equipment Suppliers.  D & L Products 
has most of the old Kepro Line of Products.


Ben