Desoldering
Desoldering:
It’s easier than you think!
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De-Soldering / Soldering Kit
User’s Manual
©
Copyright 2002
R.S.R. Electronics, Inc.
All rights reserved.
Ver. 2
0708
Introduction: Desoldering
1.0 Equipment
Two essential things are required to desolder a component:


a good soldering iron
something to remove solder
Safety Goggles
Since hot, melted solder can "splatter" a bit during
removal, a good pair of safety goggles is strongly
recommended. And, of course, you will need some
hand tools such as long-nose pliers and "picks".
Part No. 060370
1.1 Soldering Irons
The job of the soldering iron is to melt the solder so that it can be removed. So called "pencil" irons in the
15 to 35 Watt range are good for most electronics printed circuit board work. Anything higher in wattage
and you risk damaging either the component or the board. Tips for these irons come in various shapes.
Which one you use is a personal preference.
RSR 3-Wire Soldering Iron
Part No. 060501
Note that you should never use soldering "guns". They are high-power (100 Watts or more) and generate
heat by passing AC current through a loop-shaped tip. Besides the excessive heat, they can induce large
AC currents into stray loops on the board.
1.2 Solder Removers
There are three common ways to remove solder:



copper braid (usually called "solder wick")
hand-operated suction devices (spring-loaded "solder-suckers" or rubber "squeeze-bulbs")
power suction devices (motor driven, like a vacuum machine)
1.2.1 Desolder Wick
Desolder wick is fine copper braid sometimes containing a small amount of rosin
flux. Desolder wick will “wick up” molten solder much like a towel will pick up
water. To remove solder from a joint, the joint is heated. Then the desoldering braid
is applied to the joint.The solder is drawn into the braid, so leaving the joint
relatively solder-free.
The desolder wick is gentle on circuit boards, and can get into small places. It is an
essential part of a desoldering tool kit.
Desoldering Wick
Part No. 060800
1.2.2 Hand-Operated Solder Removers
Hand operated solder removers, often called "solder suckers", are an essential tool for desoldering work.
They can usually be operated with one hand. Pressing in the plunger forces air out of a cylinder. The
plunger is kept pressed by a latch. When a button on the side of the tool is pressed, a spring forces the
plunger back out at high speed. That causes a temporary vacuum that will suck melted solder off the
board. They can be very useful for removing solder from the pins of ICs and other devices.
Desolder Pump
Part No. 0608RD7382
1
Because of the force of the vacuum, solder suckers can also pull the copper pads off the circuit board.
Small pads on single-sided boards with non-plated-through holes are especially liable to be pulled off a
board. CMOS devices might need a pump which is Electro-Static Discharge (ESD) safe. Also, the nozzle
tips will need replacing occasionally.
Another popular hand-operated suction tool is the simple
rubber bulb shown here. Its advantage is that the amount of
suction can be controlled by squeezing the bulb more or less.
It can also be used to blow melted solder out of a hole
Desoldering Bulb
Part No. 060825
With both the spring activated solder sucker and the rubber bulb sucker, eventually solder will build up
around the tip and also inside the unit. So periodically they must be disassembled and cleaned out. Note
that during disassembly your fingers and hands will probably become covered with the fine solder dust
that the tools contain. Be sure to wash your hands thoroughly to remove that powder before eating.
Both the spring-loaded solder-sucker and the rubber bulb sucker can be obtained mounted on a soldering
iron for one-hand operation.
Electric Desoldering Tool
Desoldering Iron
Part No. 060848
Part No. 060849
1.2.3 Powered Solder Removers
The ultimate in desoldering technology is a vacuum powered piece of equipment as shown below. While
more expensive than the tools shown above, a powered unit can be a worth-while investment for any shop
that does a large amount of desoldering on an on-going basis. For occasional desoldering, such a unit
would be "over-kill".
Desoldering Station
Part No. 0608968ESD
2.0 Technique
2.1 Preparing the Surface
Remove any dirt, grease, varnish, epoxy, or glue off the solder joint before you start heating. Otherwise,
you can foul the tip of your soldering iron pretty quickly.
2.2 Applying Heat
Place the tip of the soldering iron against both the component lead and the board. Place it firmly, but do
not push too hard or you will damage the tip of your iron and perhaps the component as well. Normally, it
takes only two or three seconds to melt the solder, but larger components can require more time.
Sometimes it is necessary to apply a small amount of solder to "wet" the solder you wish to remove in
order to transfer enough heat to melt it.
2
2.3 Removing Solder
2.3.1 Using Solder Wick
Lay the wick over the solder joint and put the tip of the iron onto the wick. Press down firmly but not too
hard. When the wick is hot enough, the solder will melt and the wick will soak it up. When a section of
wick is filled with solder, cut it off and pull some more off the spool. Take care that you don't allow the
solder to cool with the braid adhering to the work, or you damage the copper traces when you attempt to
pull the braid off the joint. Caution: copper conducts heat very well; don't burn your fingers on the braid!
2.3.2 Using a Solder Sucker
Push down the plunger so it locks into place. Usually, you will feel or hear a click. If the tool has been
used before, a small "plug" of solder may be pushed out of the nozzle. If so, remove it. Once the solder
sucker is cocked, put the nozzle over the molten solder and press the button. The plunger will pop up
quickly taking the solder with it. This should remove most, if not all, the solder from the joint. You may
need to repeat this step a few times in order to get all the solder.
2.3.3 Cleaning Up and Touching Up
You may wish to remove any resin and left over solder from the circuit board and/or component. There
are commercial products available to take off the resin, but 000 steel wool works well of you are careful.
Solder wick can be used to "touch up" any remaining solder.
2.3.4 Reusing a Damaged Circuit Board
If you wish to reuse the circuit board, then you must repair any damage caused by desoldering.
Occasionally, you may lift a pad from the board without breaking the traces. If so, then it should be ok to
just leave it; a replacement part can hold the pad in place. If you actually break a trace, you will need to
use a small piece of wire to connect the pad to where it is supposed to go. Follow the trace until you find a
suitable location for soldering, usually the next closest solder joint. Then, solder the wire between the two
points. You can use a multi-meter set to Ohms to check continuity of traces after you removing
components.
3.0 Tips and Suggestions
Heatsinks. If you use a low-wattage iron, then usually heatsinks are not required as long as you melt and
remove the solder quickly. If you expect the desoldering of a component to take a long time, you can use
a clip-on heat-sink. But usually a pair of long-nose or needle-nose pliers is all you need.
Keep the iron tip clean. A clean iron tip means better heat conduction. Use a damp (not soaking wet)
sponge or cloth to clean the tip from time to time as you work.
Use both a solder sucker and solder wick. Use a solder sucker to
remove the majority of the solder, then follow up with the wick to
remove what's left
Other tools. You can use dental picks or specially designed tools
to help free wires and components from the melted solder.
Solder Aid Kit
Part No. 060830
3
4.0 Tutorial: How to Desolder
You will use the RSR Desoldering Practice Board to develop a valuable and necessary skill-set for the
Electronics Technician: the desoldering and removing of components from a printed circuit board (pcb).
This manual is designed to be a tutorial and a hands-on application.
As the name implies, desoldering (or desoldering) a component is the opposite of soldering a component
into place. There are several reasons why we may want to desolder a component:



Component Repair: we need to remove a defective component and replace it with a good one.
Fixing Bad Solder Joints: sometimes the solder connections on a component are "bad", causing
intermittent failure or noise. It may be necessary to remove the old solder and replace it with new
solder. A poorly soldered joint is often called a "dry joint". Usually dirt or grease prevented the
solder from melting onto the parts properly, as indicated by the solder not spreading out. The
solder will look like beads or globules.
Salvage: we wish to save some expensive and/or hard to get components from an assembly that is
being scrapped.
After completing the steps in the procedure below, not only will you have gained new skills, you will also
have a stock of electronics components you can use to build breadboards and prototypes of your own
circuits.
4.1 Safety Information
Solder is an alloy, usually of tin and lead which is melted to join other metal surfaces. Wash hands
thoroughly with soap and water after handling solder, and especially before eating or smoking. Most
soldering and desoldering irons or tools work at around 250ºC or 480ºF. Care should be taken while
handling these tools. Solder on a fire resistant surface. Never leave your iton plugged in and unattended.
Never set your hot iron down on anything other than an iron stand.
Flux is a sticky liquid or paste used to react with and remove compounds from the surface of the
connection, to improve flow of the molten solder, and to prevent oxidation during the heating cycle. Flux
tends to spit when hot. So always wear some form of eye protection like goggles or face shield when
soldering. When heated during soldering, rosin fluxes give off fumes containing many chemical
compounds. These can cause irritation, occupational asthma, birth defects, and other health problems
including cancer. If you are pregnant, or considering it, you should consult with your doctor before using
lead or solder.
Solder/Desolder only in a well ventilated
area, and use an exhaust device that
moves solder fumes away from your
face. It’s preferable to exhaust outside
(check local/state building codes and
restrictions on venting to outside air). If
you do not exhaust to the outside, use a
bench top fan or intake device with a
replaceable smoke/fume absorber. The
filter should be activated charcoal. When
ventilation is not sufficient, an OSHA
approved respirator available for fumes
should be worn.
Fume
Absorber –
Bench Top
Part No. 060860
The above information is for guidance only and user must refer to the Material Safety Data Sheet
relevant to solder and desolder wick before use.
4
4.2 Procedure
Step 1: Power Transistor Q3
Identify TO-220 transistor and remove the screw attached to the heat-sink. Remove Q3.
Step 2: Heat-sink
Identify heat-sink and remove.
Step 3: Buzzer
Identify buzzer BZ1. Notice that buzzer is mounted on the underside of board.
form the top of board and remove.
De-solder
Step 4: Power Connectors
Identify power connectors J1 and J2 and remove.
Step 5: Power Transistor Q2
Identify power transistor Q2 and remove the screw. It might be helpful to straighten the pins
before removal.
To help you become familiar with the resistor color code you can print a free copy at
http://www.elexp.com/t_resist.htm
Step 6: Large Power Resistors, 0.10 Ohms (BLK BRN BLK SIL)
Identify and remove large power resistors R1 and R6.
Note: On a 5-BAND-CODE as shown on the resistor color guide, the fourth band is the multiplier.
Step 7: Transistors Q1 and Q2
Identify transistors Q1 and Q2 and remove.
Step 8: LEDs D1 and D2
Identify regular LEDS D1and D2 and remove.
Step 9: Bipolar LEDs (Two LEDs in one package) D3 and D4
Identify bipolar LEDs D3 and D4 and remove.
Step 10: Ceramic Disk Capacitors, 100,000 pF (104)
Identify and remove all the 0.1uF disk capacitors. How many did you remove?
Step 11: 470  Resistors (YEL PUR BRN)
Identify and remove all 470  resistors. How many did you remove?
Step 12: 24 K (24,000 Ohm) Resistor
Identify and remove the 24 K resistor. What colors are on them?
Step 13: 10 K (10,000 Ohm) Resistors (BRN BLK ORA)
Identify and remove all 10 K resistors. How many did you remove?
Step 14: 2 K (2,000 Ohm) Resistors
Identify and remove all 2 K resistors. How many did you remove?
What colors are on them?
5
Step 15: 1 K (1,000 Ohm) Resistors (BRN BLK RED)
Identify and remove all 1 K resistors. How many did you remove?
The next four resistors are 5-BAND-CODE resistors with the fourth band the MULTIPLER and the fifth
band the TOLERANCE.
Step 16: 476 K (476,000 Ohm) Resistor (YEL PUR GRE ORA)
Find and remove the 476 K resistor. What is its designation on the pc board?
Step 17: 392 K (392,000 Ohm) Resistor (ORA WHI RED RED)
Find and remove the 392 K resistor. What is its designation on the pc board?
Step 18: 10 K (10,000 Ohm) Resistor (BRN BLK BLK RED)
Find and remove the 10 K resistor. What is its designation on the pc board?
Step 19: R11 (ORA BLK BRN ORA)
Find and remove R11. What value is it?
Step 20: Diode D5
Identify and remove D5.
Step 21: Integrated Circuits (ICs): U3, U4, U5
Locate and remove the ICs. See if you can identify them on-line via the internet at
http://www.datasheetarchive.com/. What are their descriptions?
IC
U3
Generic Type
HA17324 or LM324
U4
U5
HA17339 or LM339
PIC16F627-40/P
Description
Step 22: Contact Switches S1 and S2
Identify and carefully remove the tape from the switches. The switches are not soldered so
removal will be easy.
Step 23: Board Examination
Examine the stripped board to see how many (if any) pad and traces have been damaged.
6
5.0 Soldering
Good soldering results depend on a few but important steps to follow as outlined below.
5.1 Pre-heat the soldering iron for approximately five minutes, tin the tip, and roll the tip on a moistened
sponge until it appears bright and shiny. Brush the soldering iron tip on the moistened sponge prior
to each use to remove burnt rosin and to ensure proper heat transfer.
5.2 Place the pre-heated, tinned, soldering iron tip, simultaneously, against the printed circuit board foil
and the component lead for approximately three to five seconds as in Figure 1 below.
Figure 1
5.3. Apply solder to the component lead opposite the soldering iron and permit the solder to melt evenly
around the connection as indicated in Figure 2. Do not apply solder directly to the soldering iron tip.
Figure 2
5.4 Next remove the solder and then remove the soldering iron. This sequence is important as reversing
it may result in a cold solder joint. Permit the joint to cool before attempting to move the part or
otherwise stressing the joint.
5.5 The soldering joint when properly soldered should appear bright and uniform with an even miniscus
as indicated in Figure 3 below.
Figure 3
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