Opinion of low melting point solders value vs. cost - Page 1
Forum section: electronics / general

author: cdev
author_rank: Super Contributor
timestamp: February 04, 2018, 11:58:38 pm
content: Okay, so now I am convinced that Chip Quik and similar low melting point solders are a great thing to have around to get parts off of PCBs without heating them up too much.What is the best deal on more than just a tiny bit thats not going to break the bank?

author: tautech
author_rank: Super Contributor
timestamp: February 05, 2018, 12:09:44 am
content: MostlyI just use a normal Pb solder to dilute whatever solder a manufacturer cares to use but I keep a roll of 2% silver mix that I bought 20+ years ago. Infrequently I need to drag it out these days now I have a pretty ordinary soldering station but it has saved the day many a time in the past. It was 2-3x the price of Pb solder and that ratio hasn't changed much but despite the price when I run out (unlikely) I'd have no hesitation in getting more.Forget the price and just get some, the wallet and regret won't remember when youreallyneed it !

author: helius
author_rank: Super Contributor
timestamp: February 05, 2018, 12:12:14 am
content: Worried about cost? How about pouring $50,000 of lead out onto the ground?

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2018, 12:15:20 am
content: I don't think the cost varies much. Fortunately a little goes a long way, I've had the same little coil of Chip Kwik for several years now.

author: cdev
author_rank: Super Contributor
timestamp: February 05, 2018, 12:23:26 am
content: I have some silver solder, but I was specifically talking about for desoldering things like big SMD devices.Although you're right, the ROHS lead free solder requires a LOT more heat. Is that what you mean by having some 2% silver tin and lead solder?Quote from: tautech on February 05, 2018, 12:09:44 am

author: tautech
author_rank: Super Contributor
timestamp: February 05, 2018, 12:29:10 am
content: Quote from: cdev on February 05, 2018, 12:23:26 amYep.We're really discussing TH rework but for SMD similar principles apply....stick that Pb free muck where the sun don't shine.QuoteThen a PCB preheater and hot air is what you need.

author: Nusa
author_rank: Super Contributor
timestamp: February 05, 2018, 12:43:30 am
content: Quote from: helius on February 05, 2018, 12:12:14 amDoesn't pass the math test. 9000 lbs of lead at todays lead price of $1.21/lb = $10890 for the high end.I assume they're smart enough to use recycled and scrap lead rather than new ingots, so cut that price significantly.

author: cdev
author_rank: Super Contributor
timestamp: February 05, 2018, 01:17:15 am
content: I have both and intend to use the low melting point solder in combination with them.Quote from: tautech on February 05, 2018, 12:29:10 am

author: helius
author_rank: Super Contributor
timestamp: February 05, 2018, 01:19:41 am
content: I don't think your original question was actually answered (and my post also didn't help, sorry about that).Low melting-point solders are principally composed of bismuth and/or indium. Bismuth is somewhat more expensive than tin, and indium is quite expensive, around half the cost of silver. But what we really want is a solder that can alloy with either Sn60Pb40, or lead-free, and form a combined alloy that is still low melting (and maybe has a wide plastic zone). I remember some user here from Eastern Europe said that he could buy some bismuth alloy very cheaply compared to what ChipQuik costs, but I don't remember the details.

author: cdev
author_rank: Super Contributor
timestamp: February 05, 2018, 05:35:31 pm
content: Yes, thank you!Indeed you can buy bismuth crystals online, at one point I stumbled across some for sale. It's pretty stuff, very colorful.Its sold on ebay, for example.And, its not that expensive. Maybe $30 for a kilo if you're not looking for mineralogy specimens for display as art.I don't know how toxic it might be in its pure state, it might be. That should be easy to find out, though.Suppose one had some raw bismuth, and some lead and tin.. I suppose you could combine the three fairly easily in a pot. But then you would have a solid block, much less useful than solder wire.How could you get wire?It might be worth it to save money, if you saved a very lot. And used a lot of it.But I guess we all likely would like to know if any of the better very low melting point solders (desoldering solders) are a particularly better deal than the others, if we buy slightly more?I know that I just hate paying too much for anything.Quote from: helius on February 05, 2018, 01:19:41 am

author: helius
author_rank: Super Contributor
timestamp: February 05, 2018, 06:36:25 pm
content: Bismuth and indium are both "non-toxic", like silver or gold, although eating them isn't really recommended. You have to watch out because some low-melt alloys contain cadmium, antimony, or arsenic. The one that presents a particular concern is cadmium, which has beenshown to be a workplace hazardeven in the amounts absorbed as vapor from molten metal work. ChipQuik apparently does not, andseems to be the same asBolton/Cerrolow 136 (which sells for$60/lb in bulk). ChipQuik SMD16 is 16 ft. of alloy (no flux) weighing approx. 2 oz, for $98: a markup of around 1200%, although drawing the wire has some cost.A possible alternative isField's metal, which has a similar melting point (144° F), although it is more expensive in bulk due to higher indium content. I'm not sure if it has good alloying properties with lead solder; I personally wouldn't use it for anything important without verifying this. One possibility is to buy aningotof Cerrolow 136, and use a nibbler to chew off bits of it to melt onto SMD chips in lieu of wire solder. Making wire yourself requires drawing dies and is probably too expensive and time consuming.

author: cdev
author_rank: Super Contributor
timestamp: February 06, 2018, 01:45:32 am
content: I could buy an ingot or Cerrolow 136, melt bits of it off into a pancake like sheet and then cut that with shears into thin wire-like strips?That sounds most likely to be convenient to work with.Quote from: helius on February 05, 2018, 06:36:25 pm

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 06, 2018, 12:06:43 pm
content: Quote from: cdev on February 04, 2018, 11:58:38 pmi have low melt from zephytronics for many years now that i become more and more seldom using it, maybe because i usually deal with small/cheap parts like soic8 or soic16 that a heat gun will do the job. for difficult larger or expensive parts, low melt will become handy. mine is still almost in its full quantity because i kept reusing them, so i used only a tiny bit of it.Quote from: cdev on February 04, 2018, 11:58:38 pmi can see in ebay many cheapo low melt solder now, so its better compared to how it was. my Zephyrtronics was a bit expensive iirc compared to ebay options, but still affordable. i dont regret getting it...just need to be aware that we need to clean thoroughly the part removed with low melt because if we want to reuse the part and low melt solder still on its pin, solder joint will not be strong (brittle), so a one step more hassle in cleaning if using low melt solder. fwiw..

author: helius
author_rank: Super Contributor
timestamp: February 06, 2018, 03:54:13 pm
content: Quote from: Mechatrommer on February 06, 2018, 12:06:43 pmYes, that's true.On Zephyrtronics's page they also suggest using it to alloy with the frozen solder inside a desoldering gun to make it easier to clean out. If you reuse this SnPb/LowMelt combined alloy I think it will stop being eutectic at 58°C and be less effective, but if it does work might as well keep doing it.