Last night, I stenciled my first board! Very exciting. It has 70 SMT components on it, and I had trouble with only two of them. The ATMega1284P had two or three solder bridges I had to wick up. But, the USB/Serial chip, which has very tight pins, was nearly one big solder bridge. I remember after I put the paste on that it looked like there ws no space between the pins and the paste looked thick.
Any ideas what I might have done wrong? I don’t think the stencil slid at all. Is this maybe due to too much or too little pressure when swiping the squeegie?
Any ideas appreciated.
thanks!
What was the thickness of the stencil? What was the opening size for the pads for the fine-pitch components? You normally want to reduce the size for fine-pitch components (in Protel, you make the “paste mask expansion” value negative for those pads).
Ah, I see. I didn’t think of that. The gerber for the stencil was made by Eagle, the GTP layer. I never made any effort to change the apateur size from whatever the Eagle library had. I don’t have any idea how thick the stencil is. It came from Ohararp, LLC.
jarcher:
Ah, I see. I didn’t think of that. The gerber for the stencil was made by Eagle, the GTP layer. I never made any effort to change the apateur size from whatever the Eagle library had. I don’t have any idea how thick the stencil is. It came from Ohararp, LLC.
Ryan's stencils are 0.003" IIRC, which is pretty thin as far as stencils go. You really do need to reduce aperture size for very fine pitch components, even for such a thin stencil. Check if the manufacturers have guidelines on how much paste to use, and calculate aperture size accordingly.
Okay I’ll do that. I did get s sample stencil from another vendor, who charges $85.00, but the stencil seemed much sturdier. I bought the cheap one because it was for prototype boards and I figured they probably would not work.
Does Eagle allow me to change the apateur size for pins?
jarcher:
Okay I’ll do that. I did get s sample stencil from another vendor, who charges $85.00, but the stencil seemed much sturdier. I bought the cheap one because it was for prototype boards and I figured they probably would not work.
Nothing wrong with the cheap stencils, although you need a decent technique when you're using them without a frame. Check Sparkfun's tutorials on the subject.
jarcher:
Does Eagle allow me to change the apateur size for pins?
Sorry, I use Protel, but I think this question has been answered on these forums before.
Okay thanks, I’ll do some Googling. I appreciate the help!