14 Replies Latest reply on Aug 28, 2021 8:34 AM by michaelkellett

    What has been your experience with low-temperature solder?

    James Lewis

      Recently I found Chip Quik Sn Bi Ag Solder PasteChip Quik Sn Bi Ag Solder Paste. It is a low-temp alloy with Bismuth (and Silver.) When using hot air to solder parts, or during re-work, it makes the process go so much faster. It melts around 140C. It also does not appear to need refrigeration and has a long shelf-life. With all of those positives, I'm wondering what the downsides to using it are compared to more "traditional" solder alloys.

       

      So whether positive or negative, what has been your experience when using "low temp" solder?

        • Re: What has been your experience with low-temperature solder?
          mp2100

          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

          • Re: What has been your experience with low-temperature solder?
            James Lewis

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

            • Re: What has been your experience with low-temperature solder?
              shabaz

              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).

              5 of 5 people found this helpful
              • Re: What has been your experience with low-temperature solder?
                dougw

                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...

                6 of 6 people found this helpful
                • Re: What has been your experience with low-temperature solder?
                  geralds

                  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

                  5 of 5 people found this helpful
                  • Re: What has been your experience with low-temperature solder?
                    wolfgangfriedrich

                    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.

                    5 of 5 people found this helpful
                    • Re: What has been your experience with low-temperature solder?
                      andrewj

                      Sometimes the most innocuous question leads to some really useful insights. 

                        • Re: What has been your experience with low-temperature solder?
                          James Lewis

                          No kidding!

                           

                          I love the responses from the community on questions like these.

                            • Re: What has been your experience with low-temperature solder?
                              michaelkellett

                              For prototypes I would normally use tin/lead for convenience and good results in a prototype process and then we would use standard lead free for production

                               

                               

                              I've been looking at using Tin/Bismuth solder for a new production process.

                              We need lead free and low melting point (because we have a special component that can't take more than 220C).

                               

                               

                              geralds  raises some interesting points:

                               

                              The lead issue - not a problem - the whole point is to have a lead free process, all components are bought lead free.

                              Care should be taken with whatever other coatings are used on compent pads.

                              Could be a problem with mixed assemblies (like BGA where the solder balls and the solder paste get mixed together).

                               

                              Temperature range - unless a max joint temperature of 85C is OK - then forget it. We are OK since ours is an ultra low power product with a limited temperature range.

                               

                              Adding silver, massively improves joint strength and stability.

                               

                              I'll be trying some: Sn42/Bi57.6/Ag0.4 when it arrives.

                               

                              Using low mp solder to "wash" other solder off a board for repair is fine if the alternative is a dead board.

                              The reliability of the repair will depend on the skill of the operator and other things that may be hard to estimate.

                               

                              MK

                              2 of 2 people found this helpful