Shop OBEX P1 Docs P2 Docs Learn Events
Solder mask — Parallax Forums

Solder mask

Paul BakerPaul Baker Posts: 6,351
edited 2013-03-29 05:22 in General Discussion
Does anyone know of a company which sells solder masks, I am looking for generic masks like 100-TQPF, 52-QFP, 32-soj, etc. Im not looking for a custom pcb design mask, just a mask to align to a particular part on a pcb so I can get a uniform layer of solder paste on the pad so I can use my micro tip iron·without worrying of bridging pins using the solderball technique (I can do .65 with the solder ball technique but the .5 pitch parts will probably prove to be much more difficult.

Paul

Comments

  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-01-10 21:27
    I saw this: http://www.pcbexpress.com/essentials/index.php?WT.mc_id=psovr00017
    they refer to the use of screen printing for the solder masking. Is this true? Is solder paste of the cosistency that can be pushed through standard silk mesh screen? If so I'm golden I've already got a silkscreen printing kit, all I need is to goto Pearl·down the street and pick up a new screen. Does anyone know of guidance on this issue, is solder paste caustic to either the screen or the resist? Is a special purpose resist required?
  • ForrestForrest Posts: 1,341
    edited 2005-01-11 00:26
    You're confusing terms here. Solder mask is applied to printed circuit boards during the manufacturing process to cover circuits. It's typically green (though other colors are available) and it's made of acrylic or epoxy (or both) and it's designed to resist solder.

    To apply solder paste on a board, as part of the assembly process, you'll need a solder paste stencil (commonly referred to as a stencil). They are always made from stainless steel cut with either a laser or chemical etching. If you google solder paste stencil, you'll find some manufacturers that make the small stencils. A stencil designed just to place 1 component os often called a rework stencil.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-01-11 01:16
    thanks I was confusing terms
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-01-11 01:46
    I·give up,·I can only find rework stencils for BGAs *sigh* guess Ill just have to keep doing what I have been doing.
  • ForrestForrest Posts: 1,341
    edited 2005-01-11 04:20
    What type of tip are you using on your soldering iron. The best type of tip to solder SMT IC's is oval shaped and cut at a 45 degree angle.
  • StarManStarMan Posts: 306
    edited 2005-01-11 08:20
    In case you're still interested, UTZ Technologies makes stencils if you give them a gerber file.· I have had a couple made for $250 each for some surface mount boards we produce.· I don't have the phone number at hand but I can look it up if you want.· Or you could Google it.

    Chris Isaacson
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-01-11 16:36
    Forrest: I use this one, the 1.6mm barrel version http://www.howardelectronics.com/xytronic/tips.html#wavetip I'm thinking of getting some of the flat pack box smd tips that are further down the page, it doesn't help with placing the paste but it will definately speed the soldering of components.

    Starman: I've found a few stencil service providers, however because of thier custom "one off" nature they are outside the price I am willing to pay. I was looking for prototype style mass produced one part per stencil product that I could individulally lay out and hand squegee a 1" to 2"·square area for a $20 per stencil price range. The best I can determine, there·is no such product. The closest found is http://www.stencilsunlimited.com/prototype_stencils.php·(thanks Jim)·but they make absolutely no mention of what is on the prototype stencil, and the $149.50 is outside of what I am willing to pay at this moment (I have some costs coming up wrt the SX contest and the stencil is low man on the totem pole).

    Kramer: Thanks for the insight, but a multistep process is a little more than I am willing to undertake at this exact moment. I already have several new processes Im having to learn with this project, and I don't want to risk missing the deadline fiddling with a chemical process.

    Thanks for everyone's input, if I win a prize in the contest I'll probably have a custom stencil·containing with every non-BGA surface mount footprint under the sun. Until then (or when I can afford it if I don't place) I'll get lots of rest and not drink coffee before attempting to solder smile.gif .

    Paul
  • ForrestForrest Posts: 1,341
    edited 2005-01-12 00:26
    Kramer, solder paste stencils are different from the silk screen stencils you've described. A solder paste stencil is made from a .004 to .006 inch thick stainless steel sheet that has been chemically etched or cut with a laser. Solder paste is forced thru the openings (not thru a screen) with a metal squeegee.

    Paul, you're using the optimum soldering tip. The only thing I can think of to improve your fine pitch soldering is to possibly switch to a thicker flux. I've had success with a similar assembly process using a thin coat of Kester TSF-6821 (tacky flux, water soluable) brushed on the pads before soldering.
  • wangwang Banned Posts: 1
    edited 2013-03-28 23:37
    Forrest wrote: »
    Kramer, solder paste stencils are different from the silk screen stencils you've described. A solder paste stencil is made from a .004 to .006 inch thick stainless steel sheet that has been chemically etched or cut with a laser. Solder paste is forced thru the openings (not thru a screen) with a metal squeegee. Paul, you're using the optimum soldering tip. The only thing I can think of to improve your fine pitch soldering is to possibly switch to a thicker flux. I've had success with a similar assembly process using a thin coat of Kester TSF-6821 (tacky flux, water soluable) brushed on the pads before soldering.
  • LeonLeon Posts: 7,620
    edited 2013-03-29 05:22
    Mylar and Kapton paste stencils are often used by hobbyists, they are cheaper then SS but don't last as long.
Sign In or Register to comment.