Go Back   Home > Forums > >

Solid State Talk all about solid state amplification.

Aging solder joins of power transistors
Aging solder joins of power transistors
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools
Old 21st January 2007, 07:31 PM   #11
unclejed613 is offline unclejed613  United States
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
i've occasionally seen thermally stressed solder that gets "crunchy" and has the consistency of wet concrete when melted. i usually suck this junk off with a solder sucker (it doesn't wick well, either) and replace it with fresh solder. if it's in a part of the board where there's enough heat to discolor the board, i add a little bit of silver solder, or use straight silver solder to prevent that from happening again. silver solder has a higher melting point, and will look like a "cold solder" joint compared to lead based solder, but as long as you flux it properly, it will make a good connection. btw a good flux for badly oxidized connections is ASPIRIN (not tylenol or ibuprophen) tablets, it even works on steel.... just make sure you clean it off completely afterwards, as it is an acid flux...... and don't get the fumes in your face. or you can use zinc chloride flux, which works very well, it also is an acid flux. ZnCl flux usually comes in the package with silver solder.
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 21st January 2007, 07:47 PM   #12
peranders is offline peranders  Sweden
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Aging solder joins of power transistors
Default Re: Aging solder joins of power transistors

Quote:
Originally posted by reins
Hi,

I observed degrading solder joins of the power transistors of my Accuphase amp. The Amp is thirty years old.

When I re-soldered them, they even crackled.

Has anybody experienced this phenomenon?

I think it's due to mechanical stress between the heat sink and the PCB. It could be caused by warming and cooling of the transistor.

What do you thing?
Stephan
It's correct that warming and cooling do stress the solder joints. As you say resolder them may be the solution, especailly when you have a bad connection somewhere. If you also add vibrations this degrading may become faster. Heavy parts like transformers, big caps are more sensitive for this.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 22nd January 2007, 07:38 AM   #13
AndrewT is offline AndrewT  Scotland
R.I.P.
 
Join Date: Jul 2004
Location: Scottish Borders
Aspirin and Zinc Chloride!

Uncle must do some weird experiments in his hobby room
__________________
regards Andrew T.
  Reply With Quote
Old 22nd January 2007, 08:12 AM   #14
unclejed613 is offline unclejed613  United States
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
actually, the aspirin thing i picked up when i worked at NAD. if you look at a 3140 that has the stability mod done to it, you will see caps soldered directly to the steel chassis. aspirin works as a flux for soldering to steel.

the ZnCl flux paste, i used when building prototypes for a military contract. the soldering for that equipment had to be all silver soldered with ZnCl flux paste. rosin flux was not used because it does not reconstitute the silver metal from tarnish, the ZnCl does. it's a chemical reduction AgO2+ZnCl=Ag+ZnClO2 (silver oxide + zinc chloride = metallic silver + zinc chlorate) with the heat accelerating the reduction.
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 22nd January 2007, 08:54 AM   #15
AndrewT is offline AndrewT  Scotland
R.I.P.
 
Join Date: Jul 2004
Location: Scottish Borders
so the kids are safe then!
__________________
regards Andrew T.
  Reply With Quote
Old 23rd January 2007, 04:00 AM   #16
KISS is offline KISS  United States
diyAudio Member
 
Join Date: Jan 2007
When the flux isn't removed completely all sorts of bad things happen. Thermal stress just accelerates it.
  Reply With Quote
Old 24th January 2007, 10:12 AM   #17
djk is offline djk
R.I.P
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
Click the image to open in full size.

UNACCEPTABLE

OVERHEATED SOLDER

Overheated solder has a dull, gray, frosty and/or crystallized appearance and is the result of excessive exposure to heat.

NASA-STD-8739.3 [13.6.2.b.2]

Click the image to open in full size.

heat from thermal cycling causing re-crystallized into Sn and Pb separately, then fracturing.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 24th January 2007, 10:20 AM   #18
AndrewT is offline AndrewT  Scotland
R.I.P.
 
Join Date: Jul 2004
Location: Scottish Borders
Hi Djk,
nice pic!

What service conditions lead to this type of failure?
What steps should builders/designers take to avoid the problem?
__________________
regards Andrew T.
  Reply With Quote
Old 24th January 2007, 12:10 PM   #19
audiofan is offline audiofan  Canada
diyAudio Member
 
Join Date: May 2003
Location: quebec
Great pics ! nice work.

I saw same type of failure on circuits where heat dissipation is not present or almost not.
I was shure that the soldering process was the cause of the problem, but I suspect cooling process to be too quick so leaving too much stress in joint.
Do you agree or I am wrong ?
  Reply With Quote
Old 24th January 2007, 04:23 PM   #20
djk is offline djk
R.I.P
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
The first joint was simply overheated during soldering.

The second photo is actually of a high current relay, and looks close to what I have seen on TO-3 sockets on large PA amplifiers.

As to the other questions, I am going to try and talk to the guy in the lab that runs the SEM and does failure analysis of this stuff (hopefully later today).

When I see this I generally add fresh solder, then wick the joint dry, then re-solder with Ag/Pb/Sn, about %2~%4 on the Ag (silver).
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote

Reply


Aging solder joins of power transistorsHide this!Advertise here!
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Aging of components?, restoring old DIY Christian Solid State 18 27th November 2009 07:58 PM
Driver Burn IN and Aging davecandialex Multi-Way 3 15th May 2009 07:13 AM
NOS Capacitors and aging Paul Ebert Parts 7 14th June 2006 05:09 PM
Soldering newbie. Need solder transistors onto damaged amp. GuyPanico Parts 5 12th May 2005 12:43 PM
How to Revive an Aging Amp caesar148 Solid State 2 1st July 2004 07:22 PM


New To Site? Need Help?

All times are GMT. The time now is 12:05 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki