Lead-free solder recommendation: Kester K100LD for shiny lead-free solder joins

Can you tell the difference between the contrast between the joins made with a type of SAC305 solder (top) and the K100LD solder (bottom), both from Kester? — Can you tell the difference between the joins made with a type of SAC305 solder (top) and the K100LD solder (bottom), both from Kester?

It occurred to me recently that I had no idea how much solder remained on the spool I’d been using, of the SAC305 alloy (Indium Corporation’s CW-807, a SAC305 (96.6% Sn, 3.0% Ag, and 0.5% Cu)) mentioned in this old post. Without warning, I might find myself uncoiling the final row of solder loops around the core of the green plastic spool. Almost running out of solder is hardly a cold-sweat-inducing existential hazard, but It seemed prudent to order some more. In any case, I was ready to try something new.

I use Kester-branded flux pens, so Kester seemed like the brand to try this time. From Mouser, I ordered two rolls of Kester lead-free solder: one each of “275” No-Clean Core 1 lb. with SAC305 (part# 24-7068-7601) and “275” No-Clean Core 1 lb. with K100LD (part# 24-9574-7618). The former was the same alloy that I was already using, but from a (perhaps) slightly better-regarded manufacturer. The K100LD alloy was something new, to me. Kester’s datasheet for the stuff made it sound quite promising:

K100LD virtually eliminates the occurrence of common defects such as icicling and bridging. The improved grain structure also results in shinier solder joints than traditional lead-free alloy alternatives.

When my order arrived, I weighed both spools after removing the packaging. Unfortunately, it hadn’t dawned on me that my most accurate electronic scale maxes out at 200g, and I wound up using our little kitchen scale. The spool of Kester SAC305 weighed in at 473g and the K100LD at 478g. Ten-centimeter lengths of each, weighed on the better scale, clocked in at 0.36g and 0.34g, respectively. Assuming that those weights are accurate and that there truly was precisely 1 lb. (equivalent to 453.592g) of wire on each spool, I’m starting out with about 12.6k cm of the SAC305 and 13.3k cm of the K100LD.

When I tried out the two types of Kester solder wire, by using them to attach leftover 2.54mm pin headers to a small breadboard, working with the Kester SAC305 felt pretty much like working with the Indium SAC305, but the K100LD was a pleasant surprise. Achieving picture-perfect joins, like those shown in learn-to-solder tutorials, was much easier than with the SAC305 stuff and the resulting connections are, as Kester claims, quite shiny.