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Soldering to thru-hole lead to ground plane without thermal relief

Iain

#3795

Soldering to thru-hole lead to ground plane without thermal relief | 16 June, 2000

I have 15 very large backplanes (.156" thick Au plating) that the ground pins of a high density thru-hole connector were not thermal relieved in the artwork. As a result we are unable to solder the 8 pins that connect to the ground plane. We know the design is at fault and will correct this for the next build. In the mean time I need these boards and have run out of ideas. We have tried different solder types, wave solder, hand solder every trick we can come up with and no success -- we can not apply enough heat to the board to get the solder to flow. Any ideas would be appreciated. We are even considering a conductive epoxy

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Travis Slaughter

#3796

Re: Soldering to thru-hole lead to ground plane without thermal relief | 16 June, 2000

Did you try preheating the board then hand solder? Those little heat shrink guns work great for this.

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Boca

#3797

Re: Soldering to thru-hole lead to ground plane without thermal relief | 16 June, 2000

Solder 'follows' heat.

1. Preheating is a great idea, use a baking oven to get the whole assembly up to temperature, use the preheaters in your wave solder machine (without wave) to preheat the assemblies ...

2. Or use the biggest soldering iron in your building, the wave solder machine. A wave with a slow conveyor speed can move a LOT of heat into a fab thru contact with the wave itself. However the flux may not survive and common defects would include bridging. If a solder fillet is already formed on the solder side of the fab from previous attempts then no flux will get into the barrel of the holes. In this case you have to put flux on the fab from the component side.

With both of these ideas, fab damage is a real concern, that is delamination and break down of the fab itself due to overheating. Be careful.

Boca

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#3798

Re: Soldering to thru-hole lead to ground plane without thermal relief | 17 June, 2000

A few more tricks to try:

- Got a hot air rework machine? You can get more controlled heat on the area and lower the risk of damage to the fab. I never got topside fillets un unrelieve ground planes until I went to convection preheat on my waves. I would even try putting paste in the hole from the top (since the bottom already has a fillet) and reflowing it with the hot air.

- Lower temp solder? I don't know what your performance requirements are on this assembly, but if you are considering conductive epoxy, how about lower temp solder? That might flow.

- What workmanship standards are you building to? IPC 610 B only requires topside filets for Class 3 assemblies. I'm pretty sure Class 2 exempts unrelieved ground planes, and Class 1 doesn't require them at all. I don't know what 610 C requires, but it's so new that very few people are certified to it yet.

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Brian W.

#3799

Re: Soldering to thru-hole lead to ground plane without thermal relief | 19 June, 2000

IPC-610 Rev B: Paragraph 4.1 (page 52), As an exception to fil requirements on Table 4-1 on thermal heat sink planes plated through holes, a 50% vertical fill of solder is permitted, but with solder extending 360 degrees around the lead with 100% wetting from barrel walls to lead on the solder side.

IPC-610 Rev C: Paragraph 6.3.1 (page 6-7) basically mimics the revision B.

Resistance Soldering works great in these applications. We had a Pace rework/repair system that used it. Basically, current is passed thru a set of tweezers, which you would apply to the lead (or a pin in the tweezers which you would then apply to the lead). The current dead shorts, which creates heat. Instead of heating the board, and then the lead, it does it the other way around. If you preheat the board, then use this method, you should get barrel fill.

good luck, Brian W.

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