Paste In Hole

How about a double pass with your squeegee? Of course you then have the other associated headaches from too much paste on your pads, squeeze-out, bridges, extra cleaning, etc.

reply »

What make and model of printer do you have?

reply »

There was a similar thread last week on SMTnet. Maybe the poster of that thread can help. Not everyone responds on-line.

Check the SMTnet Archives for generalities and platitudes about PIH, although there may be some good links.

Baring the obvious of not making the holes on your board so wide, try increasing the metal on the board with: * Thicker stencil. * Bigger aperture area, maybe using tear drop shapes. * Second print cycle using thicker stencil and openings on bottom side for previously printed paste, printed for non-PIH components. * High metal content solder paste. * Dispense your paste, rather than printing.

Continuing with the "obvious decrease the hole size" point, have your board fabricator plate the holes "more closed". Assuming you can get away with that across the entire board.

Sometimes its not the amount of paste you put on the board, but the amount you end-up with after inserting the components, because the dang component ends-up redepositing your carefully positioned paste deposit on the floor.

Finally, have you considered epoxy? Little bit of a rework problem, but the holes will be full.

reply »

The question is are you talking of a reflow or wavesolder process. If your talking reflow I used to use a stepped stencil to ensure I had sufficient paste and then make a double pass with my squeegees. First pass with a 45 degree rubber squeegee to force the paste into the hole, followed by a second pass with a 60 degree metal squeegee to clean up the stencil and ensure a good printing profile.

If your talking wavesolder then you have the following options. Increase the upward air pressure in your spray fluxer to ensure flux goes into the holes. Change the pressure of your chip wave to et at least some solder up the hole with out causing topside solder splashes. Reduce the conveyor speed so the hole stays in the wave longer, this is not a good solution but is gives the solder more time to wick up. (You could also try preheating the power connectors before hand insertion so they don't act as large heatsinks).

Good Luck.

Steve.

reply »

What workmanship standard are you working to? The IPC book has an allowance for boards with heatsinks or thermal masses that allow less than 75% barrel fill on through hole parts. I would suggest that you check your board layers and determine if you have ground plane layers in that area.

Brian W.

reply »

Make sure you're getting a good roll from your squeegies. Poly will "scoop", leaving less, nickel will add a little extra.

A slightly shorter blade height out of the holders will help promote a good roll- this helps push the paste into the thru holes. Found this after much head scratching- we had some blades that had been "re-edged" a number of times, they worked much better than the ones with new blades.

Careful about tightening the tolerances on your pcb thru holes, you may get a tolerance stack up and be unable to fit the connector into the pcb.

reply »