Highfields Amateur Radio Club
Constructors Corner.

This is a companion page for the How to Solder page. Some say it should be part of that page. I think that it merits its' own page.

Desoldering is required to remove failed components, re-make "dry" joints, remove components to allow for upgrades etc. I'll deal with through-hole desoldering here. Some surface mount compenents can be removed in a similar way using the desolder braid method but SMD ICs require some specialist equipment to remove properly (I know of a way to do it without the specialist equipment, but that would be another article). A proper desoldering technique can soon be acquired with practice - all you need to do is obtain some scrap boards to have a go with, and desolder to your heart's content!

Tools for the job:

Safety Goggles or Safety Glasses.

Keeps molten metal from burning your eyeballs!

A Soldering Iron of some description (of course!).

Preferably with a stand.

A Desolder pump (sucker) or Desolder Braid (Wick) or both.

Solder suckers come in 3 main types:

1: Bulb Type. Primed by squeezing the rubber bulb (over a bin or similar to catch any solder pieces that are expelled from the nozzle).

Used by releasing the bulb to suck up the hot solder.

2: Spring Loaded Type.Primed by pushing the plunger on the end down (over a bin or similar to catch any solder pieces that are expelled from the nozzle) until it locks into position.

Used by pressing the button on the side, this releases the spring pressure, allowing the internal plunger to suck up the hot solder.

This type of sucker is also available "built in" to a soldering iron. As a desolder tool the iron/sucker in 1 is easy to use, but it is only really suitable for desoldering so if you need to remove and replace a component then you will need to use this and your normal soldering iron.

3: Electric Vacuum Type.

If you've invested (they are expensive) in one of these then you won't need to read this article as you must be doing a lot of it already!

Seriously though there are many different types of electric vacuum desolder tools available, either as part of a soldering station or for stand alone use. See the operators manual for correct priming and use.

Desoldering Braid:

Basicsally this is a flux imprenated woven copper braid. Available in a variety widths, use of the correct one makes the job easier.

Solder (or electronics, not plumbers, flux).

The same type of solder (leaded or lead free) as is used on the board you are desoldering from.

Methods.

Ensure that your work area is well ventilated and nobody can accidentally touch the hot soldering iron.

If using a desoldering pump or sucker:
• Prime a spring loaded sucker by pressing the plunger down. Bulb types will need to be squeezed just before you apply them to the joint. Electric vacuum types will need energising according to their hand-book.
  
  
• With a hot soldering iron, heat the solder that is to be removed for a couple of seconds.
  
  
• Keeping the tip of the iron in place and introduce the nozzle of the (ready primed) sucker and operate the suction by releasing the pressure on the bulb, pressing the spring release button or whatever is required from your particular device. This will suck the melted solder away from the board.
  
  
• Remove the sucker and iron from the board and check to see that the solder has been removed.
  
  
• If there is still some left or it doesn't seem to have worked then wait a short while so the board can cool down (over heating boards causes the solder pads and tracks to lift, making more problems!) and try again, first adding some flux or solder (which also adds flux), this often helps (but don't over do the solder!). You could try desolder wick for the last little bit, too


If using desoldering braid:


• Select the correct width for the job in hand. Use braid equal in width to solder pad and iron tip size. You can use a slightly smaller width desoldering braid and cut at an angle to fit larger pad. Folding the braid allows more solder to be wicked in a single pass. For a larger solder beads (too much solder in the first place), a wider braid is recommended.
  
  
• Lay the braid onto the solder to be removed.
  
  
• Place a hot soldering iron (if able to set temperature, set it a bit higher than you would for soldering) on top of the braid.
  
  
• If it didn't remove all the solder on the first attempt, let the board cool down then, using a clean piece of braid (snip off any solder clogged braid and discard), try again. Repeat applications can subject component and pad to unnecessary prolonged heat, so ensure sufficent cooling between attempts.

In either case you may find that the component is still "stuck" to the board. If so, while trying to pull the component (with small pliers or tweezers so you don't burn your fingers) apply the soldering iron to each component leg in turn for a few seconds, this will melt any solder left inside the hole, and remove component.