Bismuto solder wire?

I would like to know if somebody has got some experience in using the, so called, "Bi58" (i.e. Sn = 42%, Bi = 58%) solder.

As I know solder with lead are the best (melting point around 180 C°) but I want to be a good boy: only lead-free solder. At the moment I'm using the common and cheap Sn99Cu1 (227 C° as melting point) but I'm really unsatisfied with it. I mean... it's a good solder but... damn! When you try to desolder it's a real nightmare. After two or three day it becomes hard as steal and it is so sticky! You need an atom bomb to free a pin from that obstinate thing.

Before you ask the answer is yes: I have a desoldering pump and an hot air gun, but every time is a battle. Using the hot air gun you have to reach a temperature close to nuclear fusion to melt it again.

Since the Bi58 has a melting point at just 138 C° I was thinking that it could have a workability close to the one of solders with lead added. I've examined wikipedia with attention and seems the best candidate:

Bi58. Reasonable shear strength and fatigue properties. Combination with lead-tin solder may dramatically lower melting point and lead to joint failure.[30] Low-temperature eutectic solder with high strength.[19] Particularly strong, very brittle.[17] Used extensively in through-hole technology assemblies in IBM mainframe computers where low soldering temperature was required. Can be used as a coating of copper particles to facilitate their bonding under pressure/heat and creating a conductive metallurgical joint.[60] Sensitive to shear rate. Good for electronics. Used in thermoelectric applications. Good thermal fatigue performance.[67] Established history of use. Expands slightly on casting, then undergoes very low further shrinkage or expansion, unlike many other low-temperature alloys which continue changing dimensions for some hours after solidification.[37]

Since my PCB boards are not exposed to high temperatures and I don't want to damage ICs with excessive heat while soldering pins and wires I think that Bi58 could be a good choice.

Opinions? Drawbacks?

I'm surprised you have so much trouble desoldering. I have a desolderer with a heated tip that melts the solder and then slurps it up with air, and it desolders just fine. However, I have also found that different boards seem to behave differently with soldering. Some seem to let go of the solder better. Maybe the copper composition is a factor. Currently I've found the best boards, at a reasonable price, to come from Tayda. Don't just buy a lot from some ebay vendor. Quality can be very unpredictable.

I use a quite high temp solder. I'm not sure what its melting point is, but I set my temp-controlled soldering iron at 425 C for normal circuit board soldering. That allows me to complete a good solder joint in about 2 sec. Higher temperature, lower dwell time. That's a tradeoff, but I've found no problems working at that temperature.

Tin/copper only alloy is horrid, don't use it, use the proper lead-free tin/silver/copper alloy: https://en.wikipedia.org/wiki/Tin-silver-copper

Bismuth alloy is very low melting, so components will fall off the board if they run hot (its eutectic at 138C, silicon semiconductor devices are rated to 150 or 175C)

Bitmuth is not toxic, that's a relief. But it "freezes" and expands when cooled down. That is weird. Gallium is not toxic and expands as well. It melts at 30 degrees, so that might be too low for soldering ;)

Stannol sells Bi57Sn42Ag1 with a melting point of 139 degrees Celsius. However, I don't know where I can buy a small piece to try it. The 139 degrees is indeed below the maximum temperature of many electronic components as MarkT wrote. So it can not be used as a replacement of tin-lead solder.

I'm using tin/silver/copper with a lowered melting point. Stannol KS100. It is halide-free. I think it is 217 degrees Celsius. I'm not totally happy with the resin core, so I might change to another some day. For de-soldering, I add a little new solder. Never had a problem with it, but you need solder wire with a good core to make it flow.

The fumes from soldering are bad as well. That means your health risk could be worse after changing to lead-free solder.

The fumes are from the flux, flux is rosin whatever the solder.

The importance of solder being a eutectic is that all freezes simultaneously, not fractionating
into separate phases with different melting points - that makes very pasty and poor quality
joints (and horrid to rework, as SnCu solder shows). With an alloy only eutectic mixtures
have a single freezing point.

jrdoner: I'm surprised you have so much trouble desoldering. . .

I usually use 300-310 C° for soldering and unsoldering (also with soldering pump and hot air gun). I'm really scared of damaging ICs when using higher temps. On many datasheets the manufacturer always declare that ICs tolerate max 250 C° per 5 seconds, so when soldering/desoldering I feel always like walking on eggs.

425 celsius degree seems a big risk to my eyes, but maybe I could take a try....

MarkT: Tin/copper only alloy is horrid, don't use it, use the proper lead-free tin/silver/copper alloy: https://en.wikipedia.org/wiki/Tin-silver-copper

Mmmmh... I could take a try with it. It has a lower melting point (217 C° vs 227 C° of traditional Sn99Cu1). It has also an eutectic formulation.

MarkT: Bismuth alloy is very low melting, so components will fall off the board if they run hot (its eutectic at 138C, silicon semiconductor devices are rated to 150 or 175C)

I would use bismuth just to solder pins on "delicate" devices (such has arduino boards, TFT displays and so on). On the other hand I could use tin/silver/copper alloy to solder power components (voltage regulators, caps, resistors and so on). What you think? I suppose that for pins transmitting only logic TTL signals low power/heat levels are involved.

http://www.chipquik.com/store/
These guys make some stuff that you apply to soldered parts that makes it easier to get them off the board.

Look at Chipquik Alloy.

I have a hot air rework station, and I bought nozzles that puts the airflow over all pins at once, makes taking off ICs pretty easy.
Example:

@crossroads

nice tips! Unfortunately I usually have to desolder pin headers, not SMDs. Chipquik alloy works also in that case?

The squared nozzle is also a nice trick, but maybe something heating just a single line of pins is existing somewhere?

Koepel: I'm using tin/silver/copper with a lowered melting point. Stannol KS100.

As I see Stannol produces several types of tin/silver/copper alloy, I'm lost. As I understand I should select only Halide-free products to prevent potential corrosion of contacts. So only the series Kristall400 and KS100 seems suited for me. The main difference is in the flux core adopted.

Kristal400 flux: The wire flux Kristall 400 is a halogen-free activated flux based on synthetic resins with organic acids.

KS100 flux description: contains a flux free of halogens and colophony with synthetic resins. The selected synthetic resins ensure fast wetting of the solder joint surface and thus short cycle times. - I think this is the special flux named FLOWTIN by them.

Available compositions for Kristal400:

Sn95.6, Ag3.8, Cu0.7 Sn96.5, Ag3.0, Cu0.5 Sn97.1, Ag2.6, Cu0.3

Available compositions for KS100:

Sn95.6, Ag3.8, Cu0.7

Which one is better for soldering pins??? I'm lost...

Take a look at the melting points.

Alloys with silver i find much easier, needs practice to get the temp set just right.

Lead tin is far easier it melts quickly without the gooey stage you can get with lead free.

You do not say what soldering iron you use.

For lead free it needs to be variable temperature and fairly high power.

425 celsius degree seems a big risk to my eyes, but maybe I could take a try....

I've soldered at that temperature for years. Generally, I have heat applied for about two seconds. Also, when soldering something with quite a few pins, like a Nano, I don't solder "down the line". I move to spots quite removed form each other. When I get down to a few pins which are close, I wait 3 -4 seconds between soldering.

I have never, to the best of my knowledge, destroyed a chip.

Boardburner2: Lead tin is far easier it melts quickly without the gooey stage you can get with lead free.

All eutectic solders work basically the same - its only the tin/copper stuff that's nasty and pasty because its not eutectic.

Yes you set the iron to a higher temperature for lead-free and switch off when not in use, but that's the only difference (other than no risk of poisoning).

U could try using desoldering copper wire and a soldering iron

thanks to all for the tip&tricks.

I use a temperature around 310C° with a traditional soldering iron. The idea of soldering at higher temp by jumping between not-close pins is great.

I have just ordered a small amount of KS100 to make some tests (melting point is 217C* for KS100 and Kristal400 both). Unfortunately just the 1 mm diameter seems available for small quantities.

I will keep you informed abut my impressions/results.

A question about heating and soldered pins

I understand that using solder with low melting point can be a risk. When a component dissipates a lot of heat it can melt the contacts. If so, why a lot of people working for car-tuning are using solder sleeves like the one below? I suppose that the butt has a ring of solder with low melting point, or not?

Why they are not scared of heating problems?