some silver soldering guidelines

[Tmoose]

Weller and Aladdin are pretty sketchy.
EngTips searches have come up thin.

When silver soldering multiple magnet wires slid single file into a slotted copper fork, would it be good form to flux everything before assembly?

Should the solder wire be applied near the top of the joint or the bottom of the joint?

Any other best practice tips, including decent references.

thanks,

Dan Timberlake

 

[bogeyman]

Is this silver loaded ie non lead soft solder @300c or real hard silver solder (cupro nickle) 600c stuff?

 

[Tmoose]

Solder is Alladin 450. ~96% Tin and a 3% dash of silver.
220C/430 F . That makes a difference for fluxing?

Eutectic with virtually no mush phase to set up quick. Turns out its optimum gap is 0.003 inch (no mention of acceptable gap range, sheesh), and we will have to perform a miracle or 2 to get the the double gap below 0.008, which the lack of capillary action suggests we badly need to do.

We also are only heating one part, the fork, with an iron, so heating the individual wires is primarily by solar insolation until the frisky solder reluctantly forms a bridge.

 

[ScottyUK]

Can you wash the part afterwards? The more active fluxes must be washed off after soldering; rosins can normally be be left without worry except in hi-rel applications but rosin isn't particularly active. Some of the best fluxes in terms of joint cleaning ability are the water-washable synthetics from (e.g.) Multicore Solders, Alpha Metals, etc. You MUST clean the residue off after soldering! These fluxes should be readily available from the industry suppliers.

If this is a one-off job with small diameter wires look for a cored solder wire containing a water-washable flux and make sure you get the residue thoroughly removed after soldering.

Personally I'd work from the closed end of the joint out over, but see what works best. You should be a good 30 - 40[°]C above the 'mush' point to form a decent joint.


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If we learn from our mistakes I'm getting a great education!

 

[Tmoose]

We're making a few dozen solder joints for a verification build, then a batch more for a working prototype.
So far all the joints look pretty poor to non-electrical me.

The flux we/they are using is some hellishly expensive water soluble electrical grade stuff.

 

[ScottyUK]

Can you expand a little on "all the joints look pretty poor"? A 96S solder will never give the brilliant surface shine of a 60/40 or Sn62 alloy. If the joint looks uneven or lumpy then it is likely a process problem rather than the solder. Inadequate heat is a definite possibility for a lumpy joint, as is too long a working time. Some electrical fluxes have a short 'active' life once at soldering temperature. I'd speak to the technical guys at one of the companies I mentioned earlier to discuss the application and assembly process. They have (had?) entire departments dedicated to fluxes.


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

Scotty is right on,(as usual), get help from the solder maker.

If you need to, take pictures. Do a movie. Get someone in the know to check out your method. Very tiny errors can make a large difference in your joint qualities.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Tmoose]

"When silver soldering multiple magnet wires slid single file into a slotted copper fork, would it be good form to flux everything before assembly?"

I am looking for guidelines of good solder technique, as a starting point, since I am worried we may be simply ignoring some basic stuff.

Here is an image of the latest unsuccessful solder joint that our soldering senior manufacturing engineer produced. No pre-cleaning, no pre-fluxing, no pre-tinning. The 7 wires are 0.072 X 0.14 " rectangular mag wire. The 30 gram "fork" is about 0.2 inch thick, and the fork's hammer head face is in light contact with a nomex insulated aluminum fixture, plus two steel pins, so some heat is lost to the fixture. Heat is provided by a 1000 watt resistive soldering iron squeezed on the fork. Currently No wires contact with iron's carbons, and the 7 wires are a snug slip fit (0.000 to 0.003 inch clearance?) between the fork tines, but the fork tines cut faces are tapered about 0.004" as a result of the water jet mfg process, so things are only snug at an edge.

 

[itsmoked]

Wow. Looks pretty sketchy. So how are you adding the solder? Solder paste?

Just out of curiosity have you asked anyone about just TIG welding those?(Fluxes, and expensive solders, and cleaning, be damned!)

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[bill1055]

Excellent application for TIG welding. Quite similar to a commutator riser on an armature.

 

[ScottyUK]

The fork looks to have relatively poor wettability, and the solder has not flowed properly. Second problem looks like a temperature issue, first problem is a flux problem, either the piece is not getting hot enough to activate the flux or the flux simply isn't active enough.

Is the fork an investment casting or something similar? Cast copper is not great to solder to - can you do anything to polish or machine the surface to remove some of the oxide layer? That would make things easier for the flux.

As an experiment can you get hold of a plumbing flux such as Fry's Powerflux

http://www.fernox.com/?cccpage=powerflow_flux&sub=10

and experiment with that? It is a highly active water-washable flux which is excellent with both 60/40 and 96S alloys. It needs a fair bit of heat before it becomes active, and it is absolutely vital that it is washed off properly as it is corrosive. It is too aggressive for electronics but might be an option for that assembly.

A small gas torch might be a better tool to use rather than an electric iron - one of the gas soldering irons with the burner element rather than the catalytic soldering tip would be a possibility. BTW, are you serious about a 1kW soldering iron?


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If we learn from our mistakes I'm getting a great education!

 

[MacGyverS2000]

I'm with Scotty... I would think an oxyacetylene torch and a powerful flux might be the way to go on this one. That's quite a bit of mass, so heating it up quickly before the flux dries out will be problematic.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[ScottyUK]

Oxyacetylene for soft solder?! A little propane or butane flame was what I had in mind. Something like

http://www.cooperhandtools.com/brands/CF_Files/model_detail.cfm?upc=037103590435

for example!


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If we learn from our mistakes I'm getting a great education!

 

[MacGyverS2000]

Ack, didn't mean oxy... I meant MAPP. Stronger flame than butane alone. It should require a very short burst of heat to get the mass up to temp, preventing flux burnoff. As I quickly learned while trying to plumb some hefty fixtures, MAPP was the only way to get heavy masses up to melt temps before the flux stopped doing its job. I now use it for heavy solder work, too.

I just noticed the gap is 0.2" wide, which gives me a better size relationship of the wires in the pic. That fork is about 1.5-2" long? Propane/butane may be adequate.

Dan - Owner

http://www.Hi-TecDesigns.com