turnished solder

On 11/13/2016 10:51 AM, M Philbrook wrote: > In article , > snipped-for-privacy@interlogDOTyou.knowwhat says... >> >> On Sat, 12 Nov 2016 16:56:21 -0500, the renowned M Philbrook >> wrote: >> >>> >>> >>> I know some of you work on older PC boards that may have encoder being >>> stored or operated in damp areas, it tends to cause the solder to >>> turnish and is hard to rework for repairs.. >>> >>> >>> Other than scrapping it, is there some ready made chemical that will >>> wash off the surface? Something like s Silver turnish remover? >> >> Can you post a photo? How old- tin gets really hard to solder. HASL is >> less of an issue. Cardboard has sulphur that tarnishes PCBs. >> >>> Would a peroxide and white vinegar do something for me? >> >> A Scotch and water would do something for me. >> >>> Jamie > > I could post if I had one of the boards here, its at my work bench at > work and I am home atm.. > > Making new boards with a modern design hasn't attracted the massa's > at the moment. So we do some rework (repairs) sent to us from other > divisions.

What are massa's? Do you have a spell checker?

checmical? exising? Do you have a spell checker?

occassional? Hor? Do you have a spell checker?

agressive? Do you have a spell checker or are you just naturally stupid?

You're welcome

On 11/13/2016 10:51 AM, M Philbrook wrote:

Or New Yawker. Remember Archie's "turlet"?

Not taking the time to check your spelling and grammar indicates poor work habits and makes it hard to take you seriously.

In your position I'd go for a complete do-over; remove all of the solder, clean properly, and re-solder everything, then select a spray-on or other coating to prevent future damage.

Half-ass is always the wrong way to go.

Mark L. Fergerson

I occasionally get sume really UGLY boards back for rework. Some of my customers heat their shops with soft coal and the boards come back with a black coating that is conductive enough to load down CMOS logic circuits, no less some high-impedance nodes. The stuff is also FULL of acidic stuff that corrodes the boards and makes soldering difficult. I first scrub the boards with either alcohol or soap and water and a toothbrush. That does a LOT to help things. Application of liquid flux and fresh solder usually gets things so soldering can be done without great effort.

Jon

Haven't tried soda; the bead blaster I used was dentist-sized, very easy to control. Yeah, it roughed up the board when I used it on carbonized fiberglass, but left it nonconductive (and with a nice fur of exposed glass fibers). Didn't harm any copper.

Heat the board with a hot air gun add liquid flux and scrub with a toothbrush. Flux won't hurt anything on the board, clean with distilled water or alcohol if needed.

That sounds like a mixture that would cause tarnish or corrosion.

we ordered a gal of Kester 1544 RA liquid flux today.. Had to go through the process of getting the MSDS sheet and getting it past through the politics at work.

We do use RMA flux but this stuff is better I guess, we'll see.

Jamie

Jeff, I am very interested in this wax spray. Do you have a part number or vendor you like? It would be nice to try on a current project, but googling wax spray or wax conformal coating isn't yielding anything useful for me.

Well, this is embarrassing. Way back in the 1970's and 80's, I was using wax based conformal coatings on marine and commercial radios. It was usually applied as a spray. We also applied it with a brush for touchup.

However, I can't seem to find any evidence of a wax based conformal coating with Google. Something happened in the last 40 years to make it disappear. I have no idea what might have happened. I also don't recall the exact composition.

This might be a clue as to what happened: "The military used to use waxes until they found out that some tropical microorganisms eat beeswax/paraffin mixtures, so they went to synthetics long ago."

I'll keep digging, but at this time, wax seems to be a non-product.

there are "Sheet wax sprays" which will do fine..

krylon has a wax coating spray that will stick to paint. so it should also stick to boards..

On a second note, I use Electrical Clear lacquer in a spray can.. it chips away easy for rework if needed.

Sprayon has El2000 Clear Elecrical lacquer.

Furniture polish? I don't think so. Some of the stuff never dries. Others dries hard and is brittle.

As for the Krylon "wax coating": One of the reviews proclaims: "Purchased this product to put a nice waxy finish on a wooden acrylic painted product. Shook the can well, sprayed it lightly. It never dried properly, and left a sticky, tacky finish. I wiped it will after a few hours. Still sticky and tacky..." More:

Argh. If the coating cracks or chips in any manner, water can get into the crack, thus ruining the protection. That's why silicone and urethane conformal coatings are slightly flexible. Acrylic tends to be on the hard side, but with good adhesion, will probably work.

There are plenty of sprays that will work. However, there are a few things you should look for:

1. Does it have a UV additive which can be used for inspection? In most cases, you can't tell if the coating has properly covered the PCB without a UV inspection light.
2. Can your rework the PCB after the coating is applied? Soldering through some conformal coatings leaves an ugly brown burned mess.
3. Is there a solvent to remove the coating? This is a mixed blessing. Being able to clean up a mess or overspray is useful. However, the same solvent might attack the PCB when installed in some environments.

Before picking a coating, please skim: and various conformal coating selection guides.

Varnish is UV resistant but goes on heavy and may not have a high glass to it.

Lacquer applies thinner but over time can fade and is less UV resistant. Lacquer is suppose to be more flexable without cracking.

I reworked a board today and sprayed it with Sprayon EL600, because that is all I had at the bench at the time.. I would be careful around soft plastics with it. seems to work for me.

Jamie

I think you mean gloss. Unless your PCB is exposed to direct sunlight, I wouldn't worry about UV protection.

2300 volts/mil dielectric strength. Good enough for high voltage. However, no mention of dielectric constant or loss tangent, so I can't tell if it will detune tuned circuits.

"Motor windings, switchboards, commuter ends, field coils, transformers, armatures, stator windings, rings and frames, sealing electrical electronic components, and bus bars."

Well, it doesn't mention PCB (printed circuit boards) or electronic components.

MSDS shows that it's 25% MEK, which is a really bad idea around plastic parts and components. It also contains 34% methyl acetate, another nasty solvent commonly used in nail polish remover: