PCB Repair Procedures & Techniques

[defaced]

But it is dangerous containing Cadmium and lead but according to Wikipedia a non-toxic-vapor low temp alternative is available:
"Field's metal, or Field's alloy (named after Simon Quellen Field) is a fusible alloy that becomes liquid at approximately 62 °C (144 °F). It is a eutectic alloy of bismuth, indium, and tin, with the following percentages by weight: 32.5% Bi, 51% In, 16.5% Sn.

Some things to consider:
a) does it alloy with the solder that's on the board
and
b) if it does alloy with the solder on the board, does that new alloy have the desired low temperature melting characteristics? Some molten metals are like wax and water, others love each other. You don't know what you'll get until you try or find some literature on it.

For those who have bought the commercial products,
Does the commercial stuff come with an MSDS sheet? With that and a phase diagram you can probably figure out what the composition is. Or just send it to a lab for composition analysis.

[km6xz]

Yes, it comes with the MSDS if requested.
The new alloy cleans off easily so the surface is suitable for conventional soldering after cleaning. While still in fluid phase, just brush it off with a Qtip or solder wick. A solder sucker works but tends to clog pretty quickly. It is so cool in that state you could just brush is away with a fingertip.

[J M Fahey]

a) does it alloy with the solder that's on the board
and

Yes, by definition. You'll have to wait for the regular tin-lead to melt , then add your bismuth alloy wire, which will melt instantly and mix with the original solder, lowering the new, just formed alloy's melting point.
In the table mentioned in the Wiki article, the topmost one is pure bismuth-tin-lead with no "exotics" and melts at 98ºC, less than boiling water temperature.

b) if it does alloy with the solder on the board, does that new alloy have the desired low temperature melting characteristics?

It will depend on the final mix percentage.
That's why I guess the "melter" solder wire must be bismuth-heavy, to compensate the mix.
Results will be variable, but still much lower temperature than original solder, that's for sure.
The makers probably adjusted final composition by field testing; km6xz or Rondelli mentioned having beta tested it.

[jrfrond]

I know we've been discussing this as an alternative, but there are certain cases I've found where it is irreplaceable. Surface-mount switches would be a royal pain in the ass if it wasn't for low-melt, for me anyway. I don't know who else here works on Sennheiser wireless, but they use these delicate switches in all of their transmitters, and it's THE most common repair. The switches pop off clean and quickly with low-melt.

For me, it's a Godsend.

[defaced]

I'd be interested in checking low-melt out but the up front is a little steep for a trial for a DIY guy. Would anyone be interested in doing a group buy? I'd be willing to organize it.

[km6xz]

It's only $12.99 for kit with about 1 meter of the solder, plus rosin with an applicator. That should last a DIY'er months provided that they are not removing pots and switches from double sided boards all day long. Even when using it on a high volume basis with 15 techs we used less than $100 worth a month buying in bulk. During that month it would save a few thousands $$ in time saving and saving parts that can be reused.

[Ronsonic]

I know we've been discussing this as an alternative, but there are certain cases I've found where it is irreplaceable. Surface-mount switches would be a royal pain in the ass if it wasn't for low-melt, for me anyway. I don't know who else here works on Sennheiser wireless, but they use these delicate switches in all of their transmitters, and it's THE most common repair. The switches pop off clean and quickly with low-melt.

For me, it's a Godsend.

Oh, do I like Sennheiser switches, even the counterfeit ones that break exactly the same way as the real ones. Usually, I use conventional methods on those, the switch is on a corner of the board so it's easy to get to so I wick the accessible pins and just heat and lift the far corner. A lot of the time there isn't much switch left and I'll blow it off if hot air's already going. But mostly, just an iron and wick.

I even write the customer a little note telling them how to keep their switch alive. It's turning the things off that kills them, with that two second delay ordinary people tend to keep pushing harder until something gives. So I write a little note to remind them and then they go and destroy the switch again. So it works great for me, clear conscience and one of my best dollar/minute jobs.

[Mars Amp Repair]

hello,
i agree & have been using chipquik since the 90's, too. I thought I'd throw in that MCM has it in a tube with 16ea 6.5" lengths. the leaded version is $101.00 and the unleaded is $127.00 for same amount. You generally need very little for ic's. For pots & larger items if you first remove as much solder as you can with the more conventional methods, you won't need as much of the Quik to remove them...i treat the stuff like gold & save even the smallest amount I have left on a stick even holding it in my hemostats until it's completely gone. getting my techs to be as stingy with it...that's a bit of another story ;-] glen

[jrfrond]

.....one of my best dollar/minute jobs.

Amen Mike! I'd take 100 of those a week if I could! I just purchase the original Alps switch from Mouser. They're real cheap, and of course, we use a lot of them. I just LOVE when people break 'em!