[Elecraft] Central Tendency of K2 PCB Solder Pad Widths?

[Ron D'Eau Claire]

I use a 1.6 mm chisel tip on my Hakko 936 soldering station for 99.9% of my
circuit board work including building and modifying the Elecraft K2, KX1, XV
transverters, and a variety of mini-modules, homebrewing lots of stuff and
repairing commercial gear. 

The challenge is to transfer heat efficiently. Whoever wrote the Elecraft
doc on soldering was trying to give readers some way to judge whether a
given tip is "about right", but don't take 85%-95% of the trace width too
seriously. 

Normally I place the flat side of the 1.6 mm chisel tip right against the
joint to be soldered and then add solder. If the pad is extremely tiny, I
just use the side of the chisel tip. 

Solder should flow around the joint in about three seconds if the heat
transfer is correct. The danger to the pc board trace is in letting the iron
sit on the trace too long. Eventually the heat will debond the trace from
the board. That has very little to do with the temperature of the iron (as
long as it's hot enough to melt solder) and almost everything to do with the
length of time the iron is on the trace. Many folks make the mistake of
using too low of an iron temperature, requiring a long "dwell" time on the
trace, and are disappointed to see it debond even though the iron
temperature was at 700F or below. I normally solder at 750F or 800F.

I switch tips (or irons) when soldering to a large surface area of copper,
such as the ground plane covering one side of some boards or a coaxial
connector. A whole side of a pc board plated with copper or the big fittings
on coax connectors will immediately absorb and dissipate the heat. A large
tip helps transfer heat quickly, but you should still have an iron capable
of delivering the calories of heat needed. For example, my favorite coaxial
cable connector soldering iron, especially for soldering the braid to a
SO-239 connector, is a Weller 275 watt D-550 soldering gun I've had since
about 1955.

(All I have to do is wave that big gun near most circuit boards and I'm sure
I can see them cringe!)

Ron AC7AC

 
-----Original Message-----
Hi gang,

This document on the Elecraft web site,
http://bit.ly/solderingtips
says,
"[Soldering iron] tip width will normally be in the range of 1/32" (0.79mm)
through 1/8" (3.2mm), depending upon the width of the pad to which you are
soldering. The width of the tip selected should be about 75% to 90% of the
width of the pad."

What would you estimate to be the median or modal (or just typical ;-)
solder pad width on the K2's circuit boards?

Or, to be more direct, which of the following soldering tip widths would be
best for use in building a K2: 0.80 mm, 1.19 mm, 1.60 mm, or 2.40 mm?

Or am I just splitting hairs?

Thanks very much, 73 & 72,
Jeff
NE2J (formerly WB5GWB)

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