Whoops, should have double checked these hole sizes!
http://i.imgur.com/GgJ9a.jpgI’m thinking about hand drilling larger holes. I know it’ll ruin the plating connecting the top and bottom layers but all the traces for these LEDs run on one side anyway. Is this the best way to salvage these boards?
Also, what’s up with solder tenting? I specified in my CAD program to put soldermask over these vias and only around 10% are tented.
I find when I drill out holes too small, the pad gets ripped off and then you have nothing to solder to! :x
Some possibilities:
Cut the LED leads flush and solder them “on top” of the pads- but this is not very strong if you push an LED around, it could rip the pads off.
Solder in (solid) wires that fit and stick up like a header, then solder the LED’s to that. I use resistor lead trimmings.
Use fine sandpaper and shrink the LED pins - but it looks like you need 15 thou at least.
I use a cheap set of digital calipers and double check my lead sizes.
Just keep the LED’s cool, not too much heat for RGB LED’s.
allanw:
I’m thinking about hand drilling larger holes. I know it’ll ruin the plating connecting the top and bottom layers but all the traces for these LEDs run on one side anyway. Is this the best way to salvage these boards?
Commiserations… I would try a needle file to open out the holes. I find a power drill often rips the pad off, and then repair becomes quite difficult.
If you’re making your own packages, make sure you take into account that many parts have square leads. Either measure the diagonal with calipers, or use the Pythagorean theorem knowing the thickness. Then add a couple mils.
Solder in some female header pins, then the leds should push into the headers.
Looks like the LED's legs are too thick for that to work, but you could just solder them onto the header pins. This is like redwire's #2 solution of using pieces of wire to solder them to. I think this is the safest way to go.Philipf:
Solder in some female header pins, then the leds should push into the headers.
Drilling out the holes would work too, if you have a proper PCB drill and stand. With a sharp bit at highest rpm, you get very clean holes. I agree that a normal power drill could easily jam inside the hole and damage the pad, but if you use a proper vertical stand and push it down very, very slowly, it will probably work.
Choose a diameter that makes the LEDS barely fit in the holes, so they wont easily move and break the pads. Solder them on both sides with plenty of solder to act as support.
You normally use a tungsten carbide bit for pcb drilling (HSS steel blunts quickly on the glass fibre inside), but be carefull, they are brittle. You easily break a bit if you drill out an existing hole that you have not centered properly. Pressing the drill down slowly may help avoid this.
allanw:
Also, what’s up with solder tenting? I specified in my CAD program to put soldermask over these vias and only around 10% are tented.
I am not sure what you mean by “tenting”. Did you expect that the vias would be completely covered and closed by the solder mask?
The green solder mask and white legend are applied in the factory using a screen printing process with fluid ink, then cured (probably using UV light). Ink just goes down the via hole instead of covering it. There is probably not enough ink inside the via to close it.
You typically won’t see full via tenting until you get down to 12 mil drills or so.
–David Carne
forget the holes, just file down the LED leads
you could try pulling them through a draw plate.
redwire:
Some possibilities:
- Cut the LED leads flush and solder them “on top” of the pads- but this is not very strong if you push an LED around, it could rip the pads off.
I agree with this approach. If you add solder to the back side of the pad as well, it will strenghten the joint by having a connection all the way through the board.
Use a pair of needle nose pliers to bend all the leads at a 90 degree angle. Trim off the excess material in the leads so the bent section is just as long as the pads. Then solder the LED to the pads surface mount style. With 4 points of contact and solder all the way through, it should be plenty strong. Just correct the drill sizes on your next run of boards.
-Bill
