No experience, but I like the idea. I’m always hurrying thru the soldering step (but I do want the soldered joints to look good). I’ve seen the suggested trick of using bismuth to lower the melting temperature for desoldering. Probably this’ll also be a bit easier to desolder if needed.

2year shelf life is impressive.  Edit: oh, 2 years before mixing.
https://www.farnell.com/datasheets/2020956.pdf

Related. If you're not using a screen printer, does mesh/particle size matter?

Hi James,

I've not used it much, but did find it useful for QFN, where it can take me ages to put on a part and I may need to rework it a few times, because I don't use QFNs often enough to get good at it with practice. For such a situation, it's possible to have the board heated for ages, at a lower temperature, and the part doesn't go bad. I kept a QFN chip in the solder melted state for around 15 minutes, lifting it occasionally to try to fix it's position (I know it's supposed to self-centre but that's more likely for well-designed QFN pads etc) and it still worked.. it probably would have died for that long with normal solder!

It flows a little differently compared to the usual solder paste, a slightly different consistency maybe but nothing too unusual to live with. For single qty prototypes I usually use a soldering iron and normal solder wire for most parts, so I've not tried the low-temp paste for anything other than QFN. Also it only comes in one solder-ball size. Also it takes much longer to solifidy compared to normal solder.

I think a small pot or tube of the low-temp solder is useful to keep.

Regarding ball size, I don't know about best practice, but personally I found it useful to drop a size for 0.4mm pitch parts, the larger balls were clogging up the stencil (I was using the stencil without a stencil printer).

It is pretty useful when removing components with an iron because it replaces the existing solder and stays molten long enough to move the iron around to heat up and melt the solder at all pins.

The down side is it is brittle and weak when solid, so if you leave any of it on your card those joints will be very unreliable. It isn't hard to clean off but it may not be obvious that some wasn't cleaned off.

But I could be thinking of a different ChipQuick product...

Hmm, looks like I linked to the wrong stuff. I have had the two-part mix before. The stuff I got recently was different.

I think this is what I have at the moment: https://www.newark.com/chip-quik/ts391lt50/solder-paste-synthetic-no-clean/dp/90AH6290

Hi James baldengineer

Well for me:

For many decades I have deliberately not used low-temperature solder because that has several problems.

First:

the alloy. If this is not adapted to the material of the component connections, galvanic elements are created that set the oxidation in motion.

The component and the soldering point will be destroyed. "Cold soldering point" - is basically an outgassing within the soldering point, where the connection is oxidized.

Second:

When there are power components on the circuit board and they get hot during operation.

"Warm solder moves", it comes to "flow", so that the soldering point also changes here.

In particular, if there is shaking during operation, this "cold soldering point" occurs again - broken solder.

You can't see it on the outside, but over time the components come loose and the device no longer works.

In the service company I had to repair 1000s of such broken solder joints.

They are very difficult to find because most of the time you can't see them from the outside.

Have you a microscope because that defects are often very small?

Components with a corresponding temperature range. Usually this is up to + 85 ° C.

But there are components that can be used up to 125, 150 ° C. So it is very close to the melting point of the solder.

Accordingly - what happens at minus temperatures? Especially bismuth. Is something crystallizing there?

-> Whiskers. They are not only created in the component, but also at the soldering point.

Third:

the contact resistance from one element to the next.

Wire tracks - solder - component pin.

This then has to be really checked with the appropriate measuring devices. e.g. - RF applications, i.e. the clock signal, the transmission signal in high-speed applications, etc.

Every resistor is a junction point for signal edges, generating signal losses. - Signal integrity.

So it is not easy to use a soldering method "just like that", actually, as everywhere in development, to use "any" methods.

Bismuth - interesting. I have always avoided solders with bismuth. This element has been banned from use all along, for decades. Now it is being used again.

Namely, it has properties that cannot be used everywhere. It is in many ways contrary to the properties of other elements.

Well, then I'll have to check again ...

Bismuth - Wikipedia

Here was what spoken about radiation.... hmmm....

Radiation - a no-go! in the electronics device.

It's good that you mentioned that here in Element14.

Best Regards

Gerald

One has to be very careful when using low-temp solder on existing leaded solder joints. Apparently, if there’s any lead involved, such as with pre-tinned wires or leads, the combination of Bi58Sn42 and the lead can lower the melting point to 95 C and create very weak and brittle joints that can be pried apart with a toothpick.

I use low-temp solder for all tricky to solder ICs on prototype boards only. It can never leave the lab bench! As shabaz said, it is perfect to solder QFNs, I also did BGA with hot air and low temp solder successfully.

- W.

Yes, that's an important point.

Solder - Wikipedia

Different elements serve different roles in the solder alloy:

• Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of Sn
  16Pb
  32Bi
  52 with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder. Such joints are also prone to cracking. Alloys with more than 47% Bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses. Retards growth of tin whiskers. Relatively expensive, limited availability.

Eutectic system - Wikipedia

Gerald

---

Gerald, thank you for the reply.

These are exactly the kind of points I was looking to consider. Especially the minus temperatures. I had not given that aspect any thought.

Oh right, I remember a friend telling me about that! But I had not looked into the alloy Lead(Pb) creates.