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====== How to make PCB solder paste stencils ======

You'll need: 
  - A laser cutter
  - Kapton film, I like the 1 mil thick 1 ft square sheets from [[McMaster-Carr|http://www.mcmaster.com/#2271K2]]
  - Solder paste such as [[Kester No-Clean|http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=KE1507-ND]]

Software:
  - PCB layout software (well, thats how I do it) - this example will use EagleCAD
  - [[Pentalogix ViewMate Gerber viewer software|http://www.pentalogix.com/Download/download.html#item8]]
  - [[PDFCreator|http://sourceforge.net/project/showfiles.php?group_id=57796]] or some other free PDF printer

===== Create Gerber files of cream layer =====
This is the PCB we'll be making a stencil for. It only has one chip but of course you can use a more complex layout

{{:laserinfo:eagle.gif|}}

Your PCB software should be able to create/export the Cream Layer (solder paste layer) in Gerber RS274x format. In Eagle you can make your own Job for this quite easily

{{:laserinfo:creamjob.gif|}}

Also export the Dimension layer (PCB outline) since that will help a lot in registration

===== Import cream Gerber in ViewMate =====

Start up ViewMate and File>Import>Gerber one of the Gerber files generated

{{:laserinfo:import.gif|}}

{{:laserinfo:swelled.gif|}}

You can zoom in using the Magnifying glass tool

{{:laserinfo:closeup.gif|}}

===== Swell pads =====

Next we will make minor adjustnents to shrink the pads a little

Select Setup>D Codes

{{:laserinfo:dcodes.gif|}}

Which will bring up a list of all the pads used. You will probably just want to select all of them

{{:laserinfo:pads.gif|}}

Then select Operations>Swell

{{:laserinfo:swelling.gif|}}

and input somewhere around -0.002 (2 mil) to shrink all the pads by 0.002 inches in each direction

{{:laserinfo:2mil.gif|}}

You'll now see that your pads are thinner. This prevents bridging since the laser is not perfectly precise and tends to 'go over' the boundaries by a few mils.

{{:laserinfo:postswell.gif|{{:laserinfo:postswell.gif|}}}}
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