solder to brass connection?

[evolDiesel]

First off, I'll confess that I know little about electrical. I'm a mechanical engineer that has the following situation:

A PCB which has a gold trace on it. This gold trace is flat and doesn't always protrude high enough above the PCB. The gold trace is intended to make contact with a brass housing for which the PCB sits inside. We press these parts in an assembly, and this is how the connection is finalized.

We have found a simple fix where we solder around the gold trace, giving us the same exact shape, except now it is proud in the shape of a dome (no longer a flat profile) running about .001" to .003" above the PCB. We are still pressing these together (the solder is cool and hard by the time they are pressed together).

And we get great results!

However, I'm concerned with the longevity of a connection using solder and brass. How will this fair against corrosion?

The solder is lead-free (if this helps).

My official question is... has anyone ever heard of this, or know of an example I can research? Are there any considerations when using solder to brass connection?

May many blessing and good luck fall upon you for helping me

evolD

 

[itsmoked]

lead-free helps exactly nothing. It harms more than it helps and is a political device.

I think you may have some serious longevity issues using your fix.

Gold does not oxidize. This why crows like it!

Solder material most definitely oxidize. The oxides that form are almost all insulators. If the voltage is high enough it will 'punch thru' the oxides and you won't notice the problem. If you have low voltages then those voltages cannot punch thru and you can get opens circuits.

If your connection somehow is 'gas tite' then this can prevent the oxidation from occurring due to a lack of oxygen getting to the joint.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[evolDiesel]

Thanks for your timely reply itsmoked

You can submerge this assembly in a gas or a fluid and it is at least very resistant due to the press fit and potting after the press fit.

However, our products operate in the worst conditions, such as the oregon coastal range in the middle of winter. Also, our customers don't feel an overwhelming need to care or properly stow the products due to an exceptional reputation only preceeded by a lifetime warranty.

The voltage is low. We use a 1/3N battery. So we're talking 3 Volts.

 

[itsmoked]

Oh ouch.. 3V not good!

You say you pot this thing?

If so can you just solder the joint? Press fit then solder.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[evolDiesel]

The current design doesn't allow us a way of soldering the PCB to the brass. Unfortunately. It seems like we come full circle to this solution quite often.

 

[itsmoked]

You should then deal with the mechanical reasons a few thousands of an inch difference is causing you. That is a poor production situation...as I guess is readily apparent to you. LOL

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

What is the purpose of the brass casing?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[evolDiesel]

To house the PCB and make contact with another assembly that contains the battery (brass sleeve). The brass housing and the brass sleeve are both threaded to screw into each other.

Picture is worth a thousand words. This isn't 1000 words lol. Sorry.

 

[MacGyverS2000]

If it's to house the PCB, why must it come down on a trace on the PCB? If it's simply to make an electrical contact between the two, a single screw would do the same thing, and apply a mastic gasket around the remaining perimeter.. let sit overnight to harden and it's waterproof.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[geekEE]

Can you add a lug and solder or bolt a wire between the PCB and the brass for a redundant connection? Or can you solder a brass shim to the PCB so that this makes contact with your case rather than using the solder as a contact?

 

[roydm]

And a little soft petroleum jelly or grease on the contacts will keep the air away from joint.
Roy

 

[evolDiesel]

I think the application is too small for fasteners.

I'd love to toss up some solidworks models/drawings. But, I'm sure I can't do that.

I appreciate all the input, but for now, I'm just trying to figure out what it means to have a soldered PROUD trace contacting a flat brass surface... for the long run?

We've also talked about boiling the assembly to try and accelerate oxidation.

I'm only concered with oxidation at this point. A redesign (at my company) would take months (not weeks) to implement. And we're trying [desperately] to bring this design to market as it's already a year (or more) late.

You know how it is

 

[MacGyverS2000]

I'm only concered with oxidation at this point. A redesign (at my company) would take months (not weeks) to implement. And we're trying [desperately] to bring this design to market as it's already a year (or more) late.

Imagine how upset customers are going to be, then, when the product starts failing in the field because you needed to get it out of the door as soon as possible. Solve the problems now with methods that are guaranteed to work (solder tab, screw, etc.) rather than trying to artificially accelerate nature and cross your fingers the test matches with reality.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[btrueblood]

I know of at least one electrical connection that is very common, and made by light spring contact between brass (or brass-plated steel) and lead/tin solder alloy. It works okay for millions of people. It's the incandescent light bulb in a standard C- or D-cell flashlight (torch in English english).

That said, the usual user's approach when the flashlight starts to dim is to give it a shake, presumably this abrades any oxide layer that has formed at the junction, and allows proper current flow to be re-established. At the very least, the rotation of the joint when the batteries are replaced will help to scrub the joint clean.

But your joint won't have any motion after it's made up, so corrosion will likely cause trouble if allowed to progress. There are chemical oxygen absorbers (corrosion inhibitors) available on the market, google Cor-Tech, among others. A small amount of a dessicant material, or at least a controlled low-humidity environment in the assembly area could help too. Finally, is there any way to purge the ass'y with nitrogen or argon prior to assembly.

 

[mcgyvr]

Can you apply a finish to the brass?
Like tin plated with nickel under-plating. Then during assembly just place the brass housing on the gold contact and then solder the 2 together.

 

[SteveWag]

Lets add millions of rear stop and turn lamps to "btrueblood's" flashlights. Spring force may be the difference. Some of the service conditions are quite severe.

Steve Wagner

 

[zeusfaber]

I'm not picturing the setup very well, so could be quite wide of the mark here - but does anyone else see a possible problem with creep in this application?

A.

 

[felixc]

Is it that the gold plated trace is lower than the surrounding solder mask?
Is it that the PCB isn't thick enough for the shells to squeeze it properly?
If the trace is close to the edge, can a brass shim sheet be placed there to ensure a proper contact?

 

[Electech79]

Lead-free solder will propagate tin growth. This is called tin whiskers the tin growth can cause the solder to become brittle and if there are a lot of vibrations and extreme temperature changes it could cause intermittent opens. I would suggest switching to tin-lead solder if the end product is only going to be sold in the US(Oregon) . you could also consider using an acrylic or silicone conformal coat this would eliminate any concern for oxidation.

 

[MacGyverS2000]

Lead-free solder will propagate tin growth.

Based upon what information? There were tin whiskers long before lead-free solder was even a twinkle in some politician's eye.

Dan - Owner

http://www.Hi-TecDesigns.com