Aging solder joins of power transistors

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another cause is vibration from a> amplifier in speaker cabinet, b> amplifier on top of speaker cabinet, c> amplifier gets transported often
(as in an amplifier used on the road a lot)

i've seen a lot of bad solder from thermal cycling on a> to220 and to3p transistors, b> high wattage resistors (many of these stand off the board and are also subject to vibration) c> switching supply transformers, d> occasionally i find op amp pins that need resoldering, usually the power pins.

relays cause their own vibration, and will need to be resoldered once in a while.

also, you may notice that some component leads will not take solder when reheated. a drop of liquid kester flux will usually cure this, if not clean the joint with solder wick, and use the wick to rub off the oxide layer on the component lead. for high temp joints use silver solder. do not use 63/37 solder for anything that is anywhere near a heat source.
 
djk said:
Overheated solder has a dull, gray, frosty and/or crystallized appearance and is the result of excessive exposure to heat.

Sigh. I see a lot of explanations like that.

Non eutectic joints by their nature, will always have dull, gray(?) frosty/crystallized appearance. Doesn't necessarily mean it's bad or overheated though.

If you keep the liquid solder against the copper too long, the alloy copper percentage will rise, leading to this appearance also. Not necessarily too much heat as in temp, but rather, time at liquid state.

djk said:
heat from thermal cycling causing re-crystallized into Sn and Pb separately, then fracturing.

Given that picture, that's not the first thing I'd come up with.

A structure like that, through thermal cycle, will try to pull the pins during cold due to tce mismatch. Add the tce of lead/tin which is 25 to the mix, and then the heat...problems.

I'd make sure the relay isn't resting on the glass, or add a compliant layer between.

And then, I'd look at the alloy purity. The texture of the solder farthest from the pins is not lookin good. Either they are gold heavy, or they've lost too much of one constituent to dross. If those relay pins or board pads started as gold plated, I'm gonna hafta hurt somebody..:mad:

Agreed, nice pics.

Cheers, John
 
another source of "pre-stress" of component leads at the factory, is the use of a saw of some type to trim component leads after wave solder..... i've seen almost new equipment with bad solder connections because of this manufacturing technique.

there's also the possibility of "poisoned" solder in the wave machine. there are certain impurities that can get into solder that cause it to not want to stick.... when i was at Apt, we regularly sent out samples scooped from our wave machine for testing.
 
AndrewT said:
Hi John,
what's the problem with soldering to gold?

If one has it, how does one avoid that problem?

Gold causes embrittlement. It is a beddy beddy bad thing to do to solder joints.

http://72.14.203.104/search?q=cache...c+gold+embrittlement&hl=en&gl=us&ct=clnk&cd=1[/url]

edit(sorry bout the html, the doc wasn't downloading)

If you have any, and I mean ANY high priced audio equipment that has gold plated leads which have been soldered to a PC board, you have to get rid of it as soon as you possibly can.

(I'll give you my shipping address)..;)


Cheers, John
 
DOH! I just got my AudioCap Theta capacitors from Parts Express in the mail. Gold plated leads. They're for a mod, so they aren't going right into the circuit board. I was hoping that your link would have some mitigation strategies or something. Uh, any suggestions for reactions other than mailing them to you?
 
AdamThorne said:
DOH! I just got my AudioCap Theta capacitors from Parts Express in the mail. Gold plated leads. They're for a mod, so they aren't going right into the circuit board. I was hoping that your link would have some mitigation strategies or something. Uh, any suggestions for reactions other than mailing them to you?
Nope, sorry.

If they are very expensive, send em to me. If they are cheap, then there's no resale value..

What, you thought I was in the fix em up business? Nah, I'm just tryin ta swindle everybody out of their high end equipment..:D

Seriously...when I have a gold plated lead, I will usually dip them in a solder pot once or twice to consume the gold. You have to dip it about a quarter inch beyond where your going to solder to. This of course contaminates the pot, and will eventually mean replacing the load.

If you don't have a pot, just pre-tin it with a nice amount of solder, feeding a little excess solder to it so a big bead forms and falls off. Basically, swamp the gold. And don't use really high temps to do it, just enough to do the job.

Pre-tin it just prior to use as the gold will usually keep the underlying lead surface solderable.

But hey, if anybody wants to give me some expensive equipment, I won't complain....e-bay, here I come..;)

Cheers, John
 
never had a gold wired component cause trouble......... i used to build LED flashlight bulbs for standard flashlights, and one type i made was an infrared spotlight bulb (for night vision equipment), and the LED was in a gold case with gold leads. never had solder problems with them, and the solder connection to flashlight bulb bases will quickly reveal soldering defects, because of the pressure applied to the solder connection on the positive contact when installed in a flashlight
 
"Sigh. I see a lot of explanations like that."

Maybe you should contact NASA, that solder joint was created for that photo in their workmanship standards manual.

The second photo shows cracking like I see on amplifier TO-3 outputs, but without the dull crystalized look. The holes on the relay board look oversized, hard for me to tell exactly what went wrong without a closer look. Relay is brass.

"any suggestions for reactions other than mailing them to you?"

Tin them, wick them dry, and then use 4% silver solder. The tin will still migrate and fracture, but the silver seems to raise the fracture strength of the joint.

"never had a gold wired component cause trouble"

You're lucky.

Every pair of Discwasher Goldens that I sold had to be fixed with silver solder.

Every old amplifier with gold transistor leads gets wicked and re-soldered before test. Fixes most BGW and Altec amplifiers that are intermittent.

Had a repair tech at work that refused to follow my instructions, had to replace $200 pin diodes after only 30 hours of thermal cycling. The solder joints looked perfect, even under 10X magnification. Absolutely no continuity.
 
I have been having failures of copperweld leads, both on film caps and resistors (solder joints look fine, no connection when measured with ohm meter).

jneutron, do you have any idea of a reasonable service life to expect for these kind of parts? What type of replacement schedule should I work out for these things?
 
djk said:
"Sigh. I see a lot of explanations like that."

Maybe you should contact NASA, that solder joint was created for that photo in their workmanship standards manual.

If that is the level of their understanding, then there is very little I can do to help them. Anybody who states that a solder joint which shows the frosted or dull finish is a result of overheating has little if any experience with soldering....experience such as actually sitting in a production line and actually performing the soldering.

I have developed production procedures in a mil environment, for every soldering process known to man (with the exception of fluxless submerged ultrasonic soldering), and the solder materials I have personally used is basically the indalloy catalog, from 60C melts to 395C. The biggest hurdle I've had to face in all that time, is to develop the visual workmanship criteria AND teach the reliability people and the inspectors what it is they are looking at. Because, most of the alloys I've used CANNOT form a shiny surface finish when it solidifies, regardless of the solder process parameters. Hydrogen belt furnace, vacuum DAP sealer, focused infrared, vapor phase....all of these techniques, regardless of operator expertise, are unable to produce a shiny 50/50 lead indium surface..this is just one alloy as an example.

BTW, many times the explanation is inaccurate, but the end result is the same..this is one such case. If the joint looks like that and a eutectic lead tin is being used, something is wrong..the inspector doesn't necessarily need to know the technical details to be able to kick it out. Note: While it's great to have inspectors who will kick out rejects based on appearance alone, it does make it harder when the good solder joints happen to look like the example being used for a bad one. You end up trying to explain to them why what you called a reject in the past, suddenly is no longer a reject? Then you end up trying to explain eutectic vs non, phase diagrams, flux modification of surface energy....things they do not have the background to understand...deer in the headlight..

Man, been there, done that. When you find an inspector who can understand that stuff, gold.....gold I tell ya...keep em, promote em..pay em well..

djk said:
"The second photo shows cracking like I see on amplifier TO-3 outputs, but without the dull crystalized look. The holes on the relay board look oversized, hard for me to tell exactly what went wrong without a closer look. Relay is brass.
I agree, without the part in hand and under a 30x stereoscope, it's difficult to tell exactly.

djk said:
"
"any suggestions for reactions other than mailing them to you?"

Tin them, wick them dry, and then use 4% silver solder. The tin will still migrate and fracture, but the silver seems to raise the fracture strength of the joint.

Agreed with your procedure. Tin silver IS stronger, not just seems to be..

djk said:
"
"never had a gold wired component cause trouble"

You're lucky.

Agreed. Murphy at work.

djk said:
"
Had a repair tech at work that refused to follow my instructions, had to replace $200 pin diodes after only 30 hours of thermal cycling. The solder joints looked perfect, even under 10X magnification. Absolutely no continuity.

Nature of the beast. Until it slaps em in the face, they don't understand why the instructions are what they are.. This kind of data point is useful to the good techs, they will learn to trust the person giving the instructions.

Cheers, John
 
djk said:
I have been having failures of copperweld leads, both on film caps and resistors (solder joints look fine, no connection when measured with ohm meter).

jneutron, do you have any idea of a reasonable service life to expect for these kind of parts? What type of replacement schedule should I work out for these things?

Sounds weird. Any idea what the underlying plating is?? What is the gold finish?

Sometimes platers will use 10 microinches of nickel as a flash prior to the gold. It acts as a diffusion barrier to the gold. Perhaps the parts are aged, and the underlying nickel has oxidized. Initial soldering may be alloying to the gold with an underlying oxide barrier remaining intact. The oxide layer being so thin, is not visible, and the gold overlaying may be supporting the meniscus and hiding the lack of a metallurgical bond to the nickel.

Same can happen with gold over copper I guess, but I've not used that as it is not good for 6 month shelf solderability nor steam age tests.

If this is the case, do a dip using R flux in a 60/40 pot set to 250C. Remove the lead very slowly, allowing surface tension to pull the soldercoat very thin. Then, inspect for de-wet. If the gold is too thin allowing oxygen to diffuse to the flash, you'll see it here.

If that's the case, you need a two step dip process. First dip is to clear the gold. Second is for refurbishing the de-wet areas. That will need an RA flux....DO NOT DO THIS FOR STRANDED LEADS IN A MIL ENVIRO, WICKING WILL KILL YA.

Repeat the aggresive flux dip until the dewets go away.

This should work for both matte gold and shiny gold, as the RA will clear the organics from the shiny levelers..

Service life is difficult to predict, as it's not clear what the underlying problem is. My guess is an underlying oxide layer being hidden by the gold/solder meniscus.


audiofan said:
I never heard about the problem with gold , how do you solder gold plated connectors ?

Honestly, I've never had a problem with soldering to gold plated connectors. I use them exclusively for all my audio needs, and have never experienced a failure due to embrittlement (that I am aware of). I think that because of the cost of gold, most vendors go thin, 30 to 50 microinches tops. Much thicker, and the user may not adequately clear the gold during soldering.

For internal use, amps and such, I'd worry about the places where heat is involved.

Cheers, John
 
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