AH6RP amateur radio blog

Kester - Alloys: "SnBi58 Alloy

* Low melt point lead-free alternative potentially suitable for some consumer electronics. Low melt point precludes its use for applications where operating temperature is close to 138C.
* Large Bi proportion greatly reduces melting point of the solder, but alloy is more brittle. Bi improves wettability, but is somewhat offset by higher oxidation rate. In the presence of lead from HASL boards or components Bi can greatly reduce thermal cycle fatigue resistance due to the formation of Sn16Pb32Bi52 (MP=95C) which can diffuse along the grain boundaries."

C&L Finescale in England offers "145 deg C Tin/Lead/Cadmium in the form of a 1.2 mm wire," product code C2002, 0.5 kg for 25 pounds. They also have eutectic tin/bismuth as a no-clean paste, but a 35 gram syringe is 27 pounds.

Here's a small quantity of Sn/Bi wire solder: Tools (at alltronics.com): "Melcor Low Temp Bismuth Tin Wire Solder... Melcor part number 16-65-019-01... includes 2 feet of 138 deg C solder (Indalloy # 281) and the instruction sheets, spec sheet and warning sheet (don't eat it). Alltronics part number 04Z054... Unit Price : $2.95". They don't mention the diameter, but from the illustration I would guesstimate 1/30" very roughly.

Melcor themselves sell 16-65-019-01 online for $1.35, 25/$32.50, apparently without the literature that Alltronics includes.

According to the table at Indium Corporation of America » Wire Products the only indium-free wire solder that is normally available with a lower melting point than the eutectic Sn/Pb/Ag alloy is Indalloy 281, 58/42 Bi/Sn, melting at 138 C / 281 F. The shear strength is poor, 500 psi, compared to 6200 for 63/37 Sn/Pb, and the conductivity about half.

Incidentally, the name in the table for the eutectic Sn/Pb/Ag alloy is Indalloy 62/36/2...! That probably negates part of my previous post; I would imagine this implies that the Radio Shack solder is most probably 1.4% Ag and not 2.0% Ag.

Common eutectic solder, 63/37 Sn/Pb, melts at 183 C, 361 F.

Indium Corporation has a spreadsheet of solder compositions here in HTML or here in an Excel spreadsheet . It lists 62.5/36.1/1.4 Sn/Pb/Ag as melting eutectically at 179 C, 354 F. It doesn't list exactly 62/36/2 Sn/Pb/Ag (e.g., Radio Shack 64-013 0.022" wire solder, 1.5 oz for about $4) but the alloy selection section of this guide from Indium mentions that it has a melting range of 179 - 188 C, or 354 - 370 F.

That's only a 4 C or 7 F difference in favor of 62.5/36.1/1.4, and 62/36/2 is actually WORSE, since it is still slushy up to 5 C / 9 F hotter than the melting point of 63/37.

52/30/18 Bi/Pb/Sn melts at just 96 C, 205 F. That's a 87 C, 156 F difference from 63/37. That seems interesting, although the only reference to it in electronics that I have found was in an explanation of why Bi/Sn/Cu lead-free solders are on hold for the next decade or so: if there were any lead at all on the board it would dissolve into the solder to form this very 52/30/18 Bi/Pb/Sn alloy, and melting at 96 C is seen as a problem.

(There are much much lower melting points available in indium-based solders, but they form brittle alloys with copper, making them useless for electronics; see the substrate metallization section in this guide from Indium.)

I haven't been able to find much about solder availability in small quantities of anything more exotic than 62/36/2, though. Bummers.

Several cautionary tales of SMD at home are in the SMK-1 trials and tribulations thread in QRP-L. (The SMK-1 was a much smaller QRP transceiver, now out of production.) The oddest piece of advice was to stretch a nylon stocking over the nozzle of a vacuum cleaner so you could find lost SMD components by vacuuming them up. Oh. On second thought, make that ONE SMD component; if you vacuum up two different unmarked components you would have to measure the eensie things before you could solder them in.

KD7S has plans for an SMD hold-down that probably contains the absolute minimum number of parts - just two. One is a bent piece of coathanger wire and the other is a wooden slat with a groove in the bottom.

A slightly bigger version of the toolpick-and-beeswax method of handling SMD's: from the Elecraft reflector.

Luke Enriquez, VK3EM, has published a 101 level discussion of soldering SMT projects in A Guide to prototyping with surface mount technology (SMT) - HTML Version. (Also available as a PDF file.)

Highlights:

• invest in a really good pair of tweezers. However, other people, including (I think) KD1JV, have suggested using a toothpick dipped in beeswax as the easiest way of handling SMT components. In particular, an accident with tweezers will send the components flying off into never-never land. Hmm: would soldering flux be a good replacement for beeswax? By the way, having tweezers on hand is essential anyway, in case you have to desolder a component.
  
• Luke recommends LMP - low melting point - solder to avoid frying components. He goes on to define LMP solder as the 2% silver variety. That doesn't sound quite right. Although I've seen a lot of people recommend silver-bearing solder recently, the solder makers do NOT show it melting at lower temperatures. More on this later, in a post about Indium Corporation.
  
• cream solder is not as good as wire solder for hand soldering with an iron; the shelf life is short, and it is easy to boil the water in the cream and splatter tiny solder balls which can cause shorts.
  

If you are on Oahu or Molokai, please join us on 146.88- at 7:30 pm HST for the EARC nightly net. No PL tone is needed. On Saturday, I am the NCS. 72/73...

Actually Steve Weber KD1JV had announced the ATS-3 was back in stock on 7/05/05 in a QRP-L posting ([QRP-L] Time to order an ATS-3!) I think he didn't update it on his homepage for at least a few days afterwards.

In the posting, he also mentioned there will be a slightly larger ATS-4 with LED display. He thinks it may be ready in a few months. It will have latching relays to change bands instead of the tiny band modules of the ATS-3. It looks to me like it probably be quite a lot more than $160, though.

My VHF Elmer's blog: wh7n.net.

The ATS-3 (also referred to as the ATS III or KD1JV Appalachian Trail Sprint-III) went out of stock about the beginning of March. KD1JV went off on a two month hike...! He put the ATS-3 back in stock about 7/13/05.

Reviews are on the eHam site. Also see AE5X's review, builder's tips, and battery life measurements and the online copy of the AT Sprint III Assembly Manual.

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