How to solder a capacitor bank without thermal pad

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incal
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Posted by incal: Sat. Dec 11, 2010 - 06:57 PM
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I am trying to build a simple capacitor bank containing 40 of 47nF 2000V MKP type capacitors. Instead of conventional PCB manufactoring I prefer to mill the PCB because there are only holes to drill.
(Think of 40 MKP type capacitors connected in paralel and placed on a copper FR4 board.

PCB is has a very large area but has no routes rather than holes.

My main concern are the thermal pads for soldering I dont want to mill thermal pads around the holes .
because: The number of modules are high and I dont like thermal pads for high current pulse signals.

What can I do except milling thermal pads around the holes?
I plan to solder the boards wit a wave soldering machine.

any ideas?

incal99

________________________________ We dream of a world where current does not need the voltage to flow.

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Learning and Information, General Electronics
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timgoh0
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Posted by timgoh0: Sat. Dec 11, 2010 - 08:10 PM
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If you are only building one, it might be feasible to preheat the board first, with appropriate heatsinking for the caps.

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ignoramus
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Posted by ignoramus: Sat. Dec 11, 2010 - 09:51 PM
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A lot will depend on the wave soldering machine.

If the preheat section os of reasonable length You may find absence of thermal reliefs is not going to be a problem.

Additionally the volume of solder in the pot and contact time with the wave will also have bearing on the final result.

Experiment. I think there is no problem as such.

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incal
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Posted by incal: Sun. Dec 12, 2010 - 06:49 AM
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Thank you for the suggestÅŸon I will try it. But I think the solder mask must exist for the wave soldering machine. this is the only minus because I dont have solder mask equipment. Can I paint it with a negative after milling without professionale hardware?
Is the mask (silk paint) cheap and easy to find? I may cut the negative solder mask through a loan laser cutting shop. (it is really cheap).

incal99

________________________________ We dream of a world where current does not need the voltage to flow.

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tlucas
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Posted by tlucas: Sun. Dec 12, 2010 - 07:38 AM
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you have a wave soldering machine?

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incal
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Posted by incal: Sun. Dec 12, 2010 - 08:08 AM
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A friend of mine has.

incal99

________________________________ We dream of a world where current does not need the voltage to flow.

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tpappano
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Posted by tpappano: Sun. Dec 12, 2010 - 09:30 AM
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I would bet you would have no problem wave soldering these. I guess I am just ancient, but in my experience, thermal reliefs and solder masks are both are relatively new concepts in wave soldering. Actually, I thought thermal reliefs were to make "hand" soldering easier. Are these 15mm pitch "box" capacitors?

Tom Pappano
Tulsa, Oklahoma

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ignoramus
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Posted by ignoramus: Sun. Dec 12, 2010 - 11:54 AM
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INCAL,

I use Taiyo soldermask. Taiyo USA are on the web.
I use a sponge roller, mix the two parts of soldermask and rol it on. Dry the soldermask according to the application information so that the photo tool does not stick to the epoxy and expose. Use Sodium Carbonate solution to develop ( wash off excess material and PTOINGGG soldermask done.

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incal
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Posted by incal: Sun. Dec 12, 2010 - 01:53 PM
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Thank you for detailed explanation. I dont have experience with professional grade PCB phototooling. I hope I can get some special paper that I can print on a laser printer and use it as negative soldermask. The holes are big and the accuracy is not high so I hope I will be able to produce the soldermask as simply as possible.

incal99

________________________________ We dream of a world where current does not need the voltage to flow.

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