physics of the cold solder joint?

[trans4funks1]

Hi,
I've been holding off asking this question. I've been soldering for 30+ years and I don't think I have ever had something I built develop a cold solder joint.

  I have used Sn62,PB36,Ag2 solder for so long I forget why it was recommended when I learned to solder.

Lately I have been having a nagging issue in my studio where some of my microphone inputs seem to block signal until a loud signal is passed through. I can replicate this problem by powering up my system and turning on the monitors etc. and then paying close attention the first time I speak (or play a drum etc.) into a microphone. I can often times hear a short crackle or fizz and then the sound will pass without issue for the rest of the day.

I have been trying to trouble shoot this issue and had thought I was isolating the variables only to notice the issue on a different input after I was sure I had narrowed down the possibilities.

It occurs to me that when I set up this installation that I was able to rationalize the purchase all the mic cables from a reliable custom cable assembler, and I am wondering if perhaps all the cable connections are somehow coincidentally aging at the same rate. I imagine that these cables are ROHS compliant and that makes me wonder if the lead free solder can age faster and differently than I am use to with the solder I grew up with.

When I asked my tech friends about possible causes of this intermittent issue I am having, some techs opined that it might be a capacitor issue, but many mentioned a cold solder joint as a possibility.

So, my question here is regarding the character of a cold solder joint, specifically one with lead free solder, and to ask if it is possible for a cold solder joint to temporarily "heal" for the duration of a work day, if voltage is made to bridge across it's impedance. If that is possible, are there any explanations about what is happening in the metal to allow this to happen?


I know it's a long shot, but I have swapped mics (both 48vDC powered, dynamic, and tube mics), swapped mic cables, swapped line cables, and swapped preamps, and I still find the issue happening.

I can print the issue into a recording so I know it occurs before my monitor chain.

I suspected that it might be my A-D-A In/Out device which is a MOTU 896 HD, but I think I have replicated the issue by patching an input chain directly to the monitors while physically bypassing the MOTU.

I am beginning to wonder if I have a roomful of cables that are all slowly developing connector issues.

FWIW the cables are all Canare star quad and the connectors are all Switchcraft XLR.

I am normally comfortable with diagnostic work... but I'm stumped on this so I thought I should ask the knowledgeable people here.

Thank You!

 

[JohnRoberts]

The symptoms you describe sounds like a dry metal on metal contact, where a very thin oxide layer is insulating the contact, When voltage is large enough it punches through the thin oxide layer and signal conducts until it oxidizes again from sitting unused.

These intermittent connection can occur in any metal on metal contact, likes jacks or switches (or bad solder joints). Channel insert jacks in consoles are notorious for developing these problems. You can trouble shoot jacks or switches by exercising them. an insert jack that doesn't clear can be bypassed temporarily with plug shorted from tip to ring.

Solder connections that never properly flowed and relied upon metal touching metal, can oxidize over time. A way to troubleshoot for bad solder joints is to tap them with a pencil eraser while listening for changes.

JR

 

[gswan]

I agree with John. These symptoms sound similar to those which occur with relays and switches whose contacts have a minimum current rating (also called a wetting current). Oxides and uneven surface contact result in audible artifacts.

 

[trans4funks1]

Thank you both, very much, for redirecting my attention to the idea of metal on metal contact.

My primary work is with field production, where we are always plugging and unplugging everything we use, so although I own and operate a small studio, I am somewhat unaccustomed to having so much equipment wired up in a semi permanent install.

Learning to understand  that the intermittent or temporary nature of a layer of oxide isn't abnormal is a relief of sorts as I have been letting my imagination conjure up visions of a worst case scenario.

Do you have any suggestions, other than frequently plugging and unplugging them, for cleaning XLR contacts?

Thank you.

 

[CJ]

all we do around here is replace 1/4 plastic jacks with metal Switchcraft stuff,

input jacks, send/return jacks, preamp in/pwr amp out jacks, all which can screw up a signal,

patch bays with plastic jacks have also caused problems,

Neutrik is also using plastic for XLR stuff,

do not know if you can still get the nice steel XLR stuff,  maybe NOS off evilbay,

 

[JohnRoberts]

I am not aware of metal vs plastic bushings having some effect on the contact integrity. More often contact metal plating type (silver, tin, gold, ?) , wear and tear, and environment (smoke, dirt, etc), matters.

I have experienced my share of bad metal and plastic jacks, while metal bushings should be more robust for say 1/4" jacks, most XLR connectors have plastic internal structures around the actual metal contacts, so metal housing there seems even less related to performance other than locking strength.   

Of course do what works for you...  The bad news is that bad jacks or switches are rarely isolated incidents, if one is acting up, others exposed to the same conditions may be suspect too. 

JR

 

[CJ]

there are good and bad plastic jacks, Marshall seems to use good quality on their amps,

sometimes the plastic warps for some strange reason over time, if the patch cord takes a lot of pushing and shoving, then this can cause problems with the contacts,
another problem with plastic is they seem to come loose all the time, you can remove the hardware by hand,

 

[Monte McGuire]

Caig DeOxit Gold (formerly ProGold) works pretty well to remove oxide from contacts, as well as to help prevent it from forming. You can get it directly from Caig here <http://store.caig.com/s.nl/sc.2/category.292/.f> or you can get it off the shelf at Radio Shack if you're in North America. <http://www.radioshack.com/deoxit-gold-g5s-6-spray-contact-conditioner-and-protectant/6400250.html>

It's the only way I know to keep a complex installation working well. Similarly, those who have complex installations who don't use it seem to have lots of these annoying, "impossible to fix" problems - this is the simple solution.

My suggestion is to use only a little bit of it and exercise the connector or switch to help it to work off the oxides. It isn't corrosive, but a lot of excess will encourage dust and gunk to collect with no extra benefit. Also try to use lint free applicators so you don't add random fibers to your connectors or switches. Q-Tips can work, but you have to then clean off the shards of cotton that inevitably get deposited.

 

[s2udio]

http://en.wikipedia.org/wiki/Petroleum_jelly

Much better than all that fancy deoxit stuff.
Keeps Jacks and XLR's working, oxide free for years.

 

[zayance]

haha thanks for the tip s2udio

http://www.rd.com/home/extraordinary-uses-for-petroleum-jelly/2/

 

[JohnRoberts]

I am not a big fan of adding goop to switches or jacks. Often the goop will accumulate dirt and dust and require future rinse and repeat cycles.

If jacks and switches are old and tired, consider replacing them with new ones.

JR

 

[zayance]

Yes of course.
But as usefull info i wasn't aware of.

 

[shot]

Some might laugh, but I've used Coca-Cola and a toothbrush to clean my bantam connectors!
??? :-[

 

[JohnRoberts]

Some might laugh, but I've used Coca-Cola and a toothbrush to clean my bantam connectors!
??? :-[

Probably better than drinking it. I've heard about using coke or pepsi to clean rust from chrome bumpers (citric acid?), or corrosion from battery terminals?

Yes it sounds funny but not funny ha ha... funny ewww.

Be sure to clean off any sticky residue, or use almost anything else.

JR

 

[mjrippe]

Some might laugh, but I've used Coca-Cola and a toothbrush to clean my bantam connectors!
??? :-[

Probably better than drinking it. I've heard about using coke or pepsi to clean rust from chrome bumpers (citric acid?), or corrosion from battery terminals?

Yes it sounds funny but not funny ha ha... funny ewww.

Be sure to clean off any sticky residue, or use almost anything else.

JR

Phosphoric acid.  A two liter bottle of Coke is a good drain cleaner too.

 

[PRR]

I used neat ammonia on brass plugs. Not long-term clean, tarnishes in a day. But in a facility which didn't get used for months at a time, it got me through some days.

Sugar-Coke sounds like a bad idea; at least use Diet (barf) Coke.

 

[s2udio]

If jacks and switches are old and tired, consider replacing them with new ones.
JR

Well its not a cure for scrap bin plugs and sockets !
Can slso be thinned down with a dash of isoprop.
Wipe of any excess with cloth.
Also good for car electrics plugs and sockets, as most of the electronics in cars  uses 5v references and logic levels

 

[sodderboy]

Coke?  Petroluem jelly?  I made a good chunk of my living fixing debacles caused by "fixes" like this.  Certainly preventing them. 

It's like the old school  ham "take a typewriter eraser to the edge contacts and git em clean!" 

Yeah, it's all fun until the contacts are ground away from the PCB.

The sugar and long list list of chem-lab additives in the Coke are bad.  The "petro" part of the petroleum jelly is bad.  These compounds eat away at everything else around them, metals and plastics, when they off-gas in the heat. 

With a "it doesn't work until I blast the signal" situation you have to go down the contact path and find the specific point where contact is lost.  Could be a connector or a pot, maybe mechanical hampered by dirt, maybe electronic hampered by cold solder or corrosion.  The break has to be found and addressed specifically.

Clean corrosion and dirt with proper products (Caig is my go-to), not by schmearing or spraying, but by applying with control, rinsing, and conditioning.  Many Caig products are "pump" now, so they do not shoot you in you eye when you try to moisten a Qtip. 

Mike 

 

[DaveP]

Mike,

CTV's made during the 70's often developed dry joints on their PCB's.  They exhibited difficult to diagnose  intermittent faults but engineers always found them eventually by warming up the board with a hair dryer then using a cool spray to various component leads until it triggered the fault. (using the thin tube on the nozzle)  It was the rapid expansion/contraction that caused movement within the joint that made it show up, properly soldered joints expand as one.

Hope that helps
DaveP

 

[s2udio]

  The "petro" part of the petroleum jelly is bad.  These compounds eat away at everything else around them, metals and plastics, when they off-gas in the heat. 

??
With all respect Thats absolute bull.....
I am not talking about slavaring it all over you PCB'S ,or squezing a tub into your faders !!
I am refering specifically to XLR ,Jack Plugs and sockets , after cleaning of course.
I was not suggesting it was a cure for a cold solder joint, which of course is another thing .
Vaseline,(in a more viscouse grade) has been used in the power electrical industry ,to prevent oxidation of busbars joints and contacts,for years.
I ran a small PA company for a few years, every six months,all cables were checked and contacts cleaned and and wiped with
Vaseline, never had a single "dodgy contact" ,and never had any plastic degrade.
All my patchbays are treated at least once a year.........with no failures of intermittent contacts