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Desoldering

1. 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 PF to help free wires and components from the melted solder 2 Solder Aid Kit Part No 060830 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 e Component Repair we need to remove a defective component and replace it with a good one e Fixing Bad Solder Joints sometimes the solder connections on a component are bad causing intermittent failure or noise It may be necessary
2. Desoldering It s easier than you think C Y A war A g ee 4 A RA A 4 a 1 ws ba Q Z RH 773 oy J on f 4 DA ae BA LU S t 3 I ze ea r i 4 E Hl 5 A 3 wa De Soldering Soldering Kit User s Manual Copyright 2002 R S R Electronics Inc Ver 2 All rights reserved 0708 Introduction Desoldering 1 0 Equipment Two essential things are required to desolder a component e a good soldering iron e something to remove solder Safety Goggles Part No 060370 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 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
3. L PUR GRE ORA Find and remove the 476 KQ resistor What is its designation on the pc board Step 17 392 KQ 392 000 Ohm Resistor ORA WHI RED RED Find and remove the 392 KQ resistor What is its designation on the pc board Step 18 10 KO 10 000 Ohm Resistor BRN BLK BLK RED Find and remove the 10 KQ resistor What is its designation on the pc board Step 19 R11 ORA BLK BRN ORA Find and remove R11 What value is 1t 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 HA17339 or LM339 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 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 c
4. Solder Removers There are three common ways to remove solder e copper braid usually called solder wick e hand operated suction devices spring loaded solder suckers or rubber squeeze bulbs e 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 4S9 water To remove solder from a joint the joint is heated Then the desoldering braid i is applied to the joint The solder is drawn into the braid so leaving the joint ca 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 O608RD7382 Because of the force of the vacuum solder suckers can also pull
5. asis 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 1s 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 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 f
6. e 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 Fume you do not exhaust to the outside use a Absorber bench top fan or intake device with a bench Top replaceable smoke fume absorber The Part No 060860 filter should be activated charcoal When ventilation is not sufficient an OSHA approved respirator available for fumes should be worn 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 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 De solder form the top of board and remove 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 p
7. eel 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
8. ins 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 Dland 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 Q resistors How many did you remove Step 12 24 KC 24 000 Ohm Resistor Identify and remove the 24 KQ resistor What colors are on them Step 13 10 KO 10 000 Ohm Resistors BRN BLK ORA Identify and remove all 10 KQ resistors How many did you remove Step 14 2 KO 2 000 Ohm Resistors Identify and remove all 2 KQ resistors How many did you remove What colors are on them Step 15 1 KO 1 000 Ohm Resistors BRN BLK RED Identify and remove all 1 KQ 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 KQO 476 000 Ohm Resistor YE
9. omponent lead for approximately three to five seconds as in Figure I below Component Lead Soldering Foil Iron Tip p Printed ZN LL Circuit 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 Soldering Iron Tip Solder N VM A 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 Soldered Joint D a Figure 3
10. 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 Desoldering Bulb suction can be controlled by squeezing the bulb more or less Part No 060825 It can also be used to blow melted solder out of a hole 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 b
11. 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 e 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 250 C or 480 F 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 giv

Desoldering

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