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Aging solder joins of power transistors
Aging solder joins of power transistors
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Old 24th January 2007, 05:11 PM   #21
unclejed613 is offline unclejed613  United States
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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.
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Old 24th January 2007, 05:31 PM   #22
jneutron is offline jneutron  United States
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Quote:
Originally posted by djk
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.

Quote:
Originally posted by djk
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..

Agreed, nice pics.

Cheers, John
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Old 24th January 2007, 05:44 PM   #23
AndrewT is offline AndrewT  Scotland
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Hi John,
what's the problem with soldering to gold?

If one has it, how does one avoid that problem?
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Old 24th January 2007, 05:59 PM   #24
unclejed613 is offline unclejed613  United States
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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.
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Old 24th January 2007, 06:10 PM   #25
jneutron is offline jneutron  United States
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Quote:
Originally posted by AndrewT
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:...=clnk&cd=1</a>

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
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Old 24th January 2007, 08:17 PM   #26
AdamThorne is offline AdamThorne  United States
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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?
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Old 24th January 2007, 08:28 PM   #27
jneutron is offline jneutron  United States
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Quote:
Originally posted by AdamThorne
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..

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
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Old 24th January 2007, 09:15 PM   #28
KISS is offline KISS  United States
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Many times boards are wave soldered but the mass of the connections fail to wet and thus you get a failure as well accelerated with flux residue, thermal and mechanical stresses.
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Old 26th January 2007, 07:26 AM   #29
unclejed613 is offline unclejed613  United States
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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
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Old 27th January 2007, 08:59 AM   #30
djk is offline djk
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"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.
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