Correct bit for soldering SMD

Nuuk said:
I am about to order a new bit for my Weller soldering iron to use specifically with SMD parts. I see that each shape of bit is available for soldering at different temperatures, ie 500, 600, 700 800 asnd 900 degrees F.

So what is the correct temperature to choose for SMD? :xeye:

The tip temp you need is generally based on the thermal mass and size of what you are soldering. I use Metcal irons at work, and the vast majority of my work is SMT. Heavier copper thickness, ground planes w/o thermal webbing, and multi-layer PWB's will require higher tip temps. I mostly use 700 d F tips, but have a few 800 F tips for the tough spots. One caveat is that the higher the tip temp, the shorter the life of the tip. Also, it's much easier to damage a PWB, or even a component. 600 F tips work well for light Cu (1/2 oz) and small things, like SOIC's and small passives. The past few projects I've worked on have all been multi-layer, with 2 oz Cu top and bottom, 1 oz internal, up to 10 layers. 700 F is a requirement.

Also worth noting is that 800 F tips are nearly impossible to keep tinned and clean. At 800 F, lead solder oxidizes nearly instantly, creating a black sooty layer on the tip that makes frequent wiping a necessity. Extended idling can ruin the tip. I use them only when absolutely necessary, and leave them on as short a time as possible.

(Note: I have no experience with high-temp solders. You may well need a higher temp tip to work with different solders. The rule of thumb is still to use the lowest tip temp you can get away with).

So, for the DIY'er doing SMT, I would get a 600 and 700 F tip, and see which works better. (For lead solder) Also, IME, avoid the needle tips, since the small thermal mass makes heat transfer difficult. My preference is for small chisel point tips. Look for tip sizes that fit the size of the components you are working with. This is probably the most important factor in tip selection.

Hope this helps.