Solder bridge clearing tips - LM3875

[nemonis]

I am currently assembling a LM3875 amp using Peter Daniel (Audiosector) PCBs. First, the boards are gorgeous. Unfortunately, I am not as skilled as I would like at soldering. His instructions mention to make sure that pins 1 & 4 have solder on the top, as these are the power pins. All well and good on my first board. I only bridges pins 4 & 5. Pin 5 has no connection per the datasheet, so that isn't a problem. The first two images (both capacitors on board) are the good board.

The second board, I managed to create a rather impressive solder bridge across pins 3-7. This is a problem. Pin 3 is output, pin 4 is negative rail, pins 5 and 6 are no connection, and pin 7 is non-inverting input. Obviously, I have not applied power to the board. I also removed the positive bulk capacitor to give myself a bit more room to work. The last three images (only one capacitor on board) are the bridged board.

Are there any suggestions for clearing these bridges? I have a desoldering bulb, desoldering braid, solder, and will have a Circuit Specialists station 1A. I was using an el-cheapo soldering iron, but managed to break a spot weld attaching the tip, so it is dead.

[Einric]

You could try heating them and using the soldering iron to draw a little away.
Clean the iron and let the pins cool.
Try again, a couple of times and you should have broken the solder bridge.
One of the spring loaded solder suckers would also work well in this application.

Once the bulk of the solder is gone you can use the braid.
Fan the braid out a little.
Press the braid to the solder in question and the solder should wick into the braid.
If you have any liquid solder flux it can help to brush a little on before you place the braid onto the solder.

[454Casull]

You can use a small file, with a right-angle edge, to remove the bulk of the solder. Thermally, this will be less intrusive.

[nezbleu]

Like Einric said, use your desoldering bulb to remove the bulk of it, then clean up with braid.

Glad to hear you are getting a better iron, which will improve your ability to do fine work. I think those solder stations cone with a conical tip, which is OK, but a fine chisel tip is better. I don't think the instructions to make sure there is solder on the top of the board mean you need to apply solder to the top, but just to hold the heat on those pins a few seconds longer and flow in a little more solder, so you can see the solder from the top. I'm sure you are aware that what is pictured above is a bit of a mess, and is way too much solder.

[sofaspud]

My advice is to forget the braid for now. Using the far right pic for reference: Have the desoldering bulb ready ie squeezed in one hand, near the work. Apply the tip of the soldering iron to that blob on the top side of the board. Watch closely and you'll probably see the little "wave of heat" move across the surface of the blob as it melts; when it reaches the end of the blob, release the bulb and suck up as much solder as possible. This complete action should take maybe 2 or 3 seconds, and don't leave the iron applied to the leads. Repeat as necessary, but twice, maybe three times, should remove that topside blob.
Then do the same with the bottom side. Here I find it often works very well to place the nozzle of the solder sucker right over the end of the leads, with the iron applied to the remaining exposed part of the lead. Of course if it is a tight fit that won't work!
Once you've done that, put some flux on the joints and reflow the solder remaining on the leads, with the iron tip applied to both lead and pad (the pin 2 joint (2nd from right) in the second pic suggests the end of the lead was hotter than at the pad), applying more solder only if necessary. Hope this helps.

[bobodioulasso]

I propose another method.
When the blob melts, shake violently the board downwards.
The solder will go away at once.

[nemonis]

Originally Posted by 454Casull

You can use a small file, with a right-angle edge, to remove the bulk of the solder. Thermally, this will be less intrusive.

I like this idea. I think this will be the first line of attack.

Originally Posted by nezbleu

Like Einric said, use your desoldering bulb to remove the bulk of it, then clean up with braid.

Glad to hear you are getting a better iron, which will improve your ability to do fine work. I think those solder stations cone with a conical tip, which is OK, but a fine chisel tip is better. I don't think the instructions to make sure there is solder on the top of the board mean you need to apply solder to the top, but just to hold the heat on those pins a few seconds longer and flow in a little more solder, so you can see the solder from the top. I'm sure you are aware that what is pictured above is a bit of a mess, and is way too much solder.

I wish I had known what was meant regarding the solder. That would have avoided the whole fiasco. I thought he meant that solder had to be applied to the top of the board, and it spiraled from there. I will keep the tip suggestion in mind for the future.

Two further question regarding clearing the solder:

• Should I plan on heating from below the board and waiting for the heat to "climb" the pins?
• Should I plan on clamping/holding the chip onto a heatsink while applying heat?

Originally Posted by bobodioulasso

I propose another method.
When the blob melts, shake violently the board downwards.
The solder will go away at once.

This idea is so crazy, it just might work! Of course, I need to make sure I am flicking solder onto a heat-resistant surface (next week, how to fix solder burns on the wife's dining-room table ).

Thank-you for all of the suggestions. I will post back once I resolve the problem.

[sofaspud]

I thought he meant that solder had to be applied to the top of the board, and it spiraled from there

If it isn't a plated thru hole, it probably does need to be applied to the top. But you seem to choose ignoring my other advice, so... good luck to you.

[5th element]

I've always used solder braid for anything like this, from sucking up small amounts of solder to rather large quantities, never had a problem with it even down to clearing gaps between 0.5 pitch SMD pins.

[mdynac]

or you could do what i do and use this....