flyrotary@lancaironline.net Mailing List Archive

We produce and test a lot of boards that are all SMDs and fine pitch devices. Getting that solder paste on the correct thickness is an art form. Even with a tightly controlled manufacturing process and state of the art equipment, there are often problems.

I saw a real nice pick-n-place machine for placing somponents on circuit boards go at auction for $500. It was probably worth 100 times that. If I were in California, I'd have bought it.

Mike LaFleur

----- Original Message ----
From: Ed Anderson <eanderson@carolina.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Friday, February 16, 2007 6:25:18 PM
Subject: [FlyRotary] Re: SMD Printer Photo 2

Hi Bill, there are a number of places that will make stencils - but cheaper plastic ones a bit harder to find.

You take a CAD drawing for your circuit board - most use DXF format but they can be make from Gerber files (my Circuit Board drawing software does not produce gerber files, but will export a DXF file).

I then eliminate anything in the DXF file that is not a pad or pin that I want solder on. Then e mail the file to this company/guy. http://www.pololu.com/ attn : Jan Malasek They use a laser to cut the stencil based on your DXF file and ship it to you. Oh, they first send you a PDF of the proposed stencil for one last check by you before cutting the stencil.

Here is the webpage that explains their process. http://www.smtstencil.com/

The one I got matches even the 30 pins of a fine pitch socket with pins only 0.25mm apart, so I was pleased. You can see some result of the laser heat on the plastic so its not quite as clean as with a metal stencil - but quite good for the price.

----- Original Message -----

From: Bill Schertz

To: Rotary motors in aircraft

Sent: Friday, February 16, 2007 4:52 PM

Subject: [FlyRotary] Re: SMD Printer Photo 2

Ed,

Very nice printer you made -- how do you get your stencils?

Bill Schertz
KIS Cruiser # 4045
----- Original Message -----

From: Ed Anderson

To: Rotary motors in aircraft

Sent: Friday, February 16, 2007 2:55 PM

Subject: [FlyRotary] Re: SMD Printer Photo 2

Hi Bill,

To answer your question, Yes. And I am certain they can be made to do the job. In fact, before the stencils arrived on the SMD scene, it appears they used a "Mesh screen" which I understand is very close to what the silkscreen printers do.

But, the "mesh screen" approach was limited by the smallest pitch of pins they could resolve to, so they went to the stencil approach.

With the solder paste method (from what I think I understand) appears to require some consistency of pressure for best results. That lead to my adjustable springs to put the squeegee under consistent pressure - supposedly once I find that magic pressure setting then consist good result will follow.

Lots of ways to skin this cat.

Ed
----- Original Message -----

From: wrjjrs@aol.com

To: Rotary motors in aircraft

Sent: Friday, February 16, 2007 3:41 PM

Subject: [FlyRotary] Re: SMD Printer Photo 2

Ed, That looks like innovative and neat work. Now the apparatus begs the question, have you ever looked at a standard silkscreen jig from the art store to do the same job? The design you made is considerably tougher, but some of the silkscreen machines are pretty well framed using hardwood. FWIW (which probably aint much)

Bill Jepson

-----Original Message-----
From: eanderson@carolina.rr.com
To: flyrotary@lancaironline.net
Sent: Fri, 16 Feb 2007 11:19 AM
Subject: [FlyRotary] SMD Printer Photo 2

This shows one of the two side mounts of my SMD solder paste printer which is attached to the MSD nylon strip which rides in a groove inside the cheap T track. The T track is simply screwed to the 1/2" slab of aluminum. The acorn nut provides tension through a 1/4" threaded rod and keeps the pull-handle gripped between the two sides and provides tension on the side plate which puts side pressure on the MSD strip in the T rail. More pressure makes the device slide slower and less makes it faster.

The squeegee holder can pivot to either put the squeegee down on the bed or to hold it up off of it after a solder run and you want to move the squeegee holder back to the other original end of the board without smearing your deposited paste.

The second photo shows where the squeegee holder would be positioned after a "solder-run" was made. I would then rotate the squeegee up 1/8" inch out of contact with the bed and move it back to the other (starting) end of the bed.

Ed

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