[Elecraft] quick (gooberheaded) solder question

[Tom Hammond]

Hi Steve:

>My soldering station is a Weller and it's calibrated in Degrees.  The K2 
>manual states 25-40 watt iron (with a tip of 370-430 deg C).  I'm assuming 
>this will be also correct for the KX-1 though I couldn't find anything in 
>the KX-1 manual that discussed solder temperature (I admit I may have 
>missed it!)  Since I'll be soldering ICs directly to the board, I thought 
>I'd write and ask the group about this before I go roasting all of my ICs 
>due to too high temps or too-long soldering time.  So I guess my question 
>is, what temperature corresponds to 25-40 watts, or is it simply the tip 
>rating (i.e., I set my station to 400 deg C)?  Obviously the lower I set 
>the iron, the longer it will take to make the joint; but too high a temp 
>will fry parts.

Unfortunately, it (watts, that is) is merely a rating, with not particular 
temperature tied directly to it... UNLESS it's a true temp-controlled iron. 
The 'wattage' does give you some indication of how quickly a 
temp-controlled iron should be able to replace missing heat at the tip of 
the iron, but if the iron's not truly temp-controlled, it's gonna be 
running balls-to-the-wall all of the time, and at whatever wattage you've 
selected... with little actual control of the tip temp, other than the fact 
that it's gonna be hotter before you touch it to the PC board pad and 
colder once you remove it.

IF you can dial in a desired temp, then you'd probably want to select 
something in the range of about 380 deg. C (725 deg. F) for most PC board 
applications and maybe something like 400-430 deg. C (800 deg. F)for those 
times when you might need to solder to a large PC board land or to a 
well-grounded (and thus well heat-sinked) PC board pad. Grounded pads tend 
to sink away quite a bit of heat, so I often try to hit them with a bit 
hotter iron, so I can heat the joint quickly and get in/out without 
dwelling too long on the joint.

>I guess I'm just too detail-oriented.  I'm nervous about putting iron to 
>PC board until I know I'm operating in a safe range.

Figure this, if you can complete a nice, well-soldered PC board joint in 4 
seconds or less, you have AT LEAST an adequate amount of tip temp. If you 
can repeatedly complete the same joints, one after the other, as when 
soldering an IC, then there's a good chance that your iron is 
temp-controlled, OR the iron's NOT temp-controlled but is WAY too hot to 
start with! A good temp-controlled iron should allow repeated 3-4 seconds 
joints just as fast as you can make them without cooling off the tip 
appreciably.

73,

Tom Hammond   N0SS