Abstract:  This application note is a basic guide to good soldering techniques that everyone should practice.  I will explain through hole and  surface mount component soldering along with how to remove them.  I have also included some tips on what to look for when you are trying to fix something that may be broken.

    Introduction:All the following techniques I will explain  in the following document come from two sources. The first source is my personal experience as a bench technician and the second more important source comes from a soldering course I took at NAIT.  The course was based upon the PACE soldering and printed circuit board repair program.  I highly recommend that you take this program if you ever have the chance.
    NASA retrained all of their technicians according to PACE standards after the Challenger explosion.  According to my instructor they reduced the weight of the shuttle by almost a ton by applying the PACE techniques.  If this is even 1/10th true it would represent a large savings due to the cost associated with launching weight into space.  Therefore, good soldering techniques can save more than expected.

    The Equipment: The following items are suggested:

                        1)    Soldering Station ( I prefer a variable temperature 600 to 800 F).
                        2)    Solder ( Rosin core only !! )
                        3)    Isopropyl Alcohol ( you can get this cheap at the pharmacy but make sure
                                its 100% pure -no additives like glycerin)
                        4)    Liquid Flux.
                        5)    Solder sucker, Chem-wik.
                        6)    Lenline fiberglass pen or ink eraser.
                        7)    Toothbrush.
                        8)    Popsicle or tongue depressor.
                        9)    Assorted Soldering Iron tips ( med. chisel, med. point, small point )
                        10)  Dental Tooth Probe, Hemostats (forceps), or any thing small and pointy.
                        11)  Fan.

    Please note solder contains lead and is a toxic substance always wash your hands after soldering and don't hold solder in your mouth ( don't laugh I have seen people do this ).   Even the fumes can be hazardous!!!

    Through Hole Soldering:  If you examine various printed circuit boards (PCB) you will notice that there are single sided and double sided ones.  Double sided boards usually have copper tubed holes meaning there is metal from the top side to the bottom side of the board as shown in the figure below.
 
 

    I will now describe how to solder to a single sided PCB or an double sided PCB with no through copper.

    1)    Before soldering you should clean the pad of the PCB lightly with the Lenline pen
           or eraser to remove surface oxides and clean the lead of the component, try to
           avoid touching either, as you will leave oils on the metal that will affect how the
            solder will flow.

    2)    Clean both the pad and the lead with alcohol, let them air dry.

    3)    When soldering on a PCB with no copper through hole you should bend the leads
            over at a 30 degree angle to the PCB as shown below.  To do this use the popsicle
            stick so if you slip you will not damage the traces and also to avoid touching the
            leads.  The lead should extend no further than the outer circumference of the pad.

    4)    The main reason for doing this is to add more surface area for soldering to.  In
           addition, this will also add some strength  if you need mount the PCB vertically.

    5)    Next apply some flux to the area.  (Hint flux is easily contaminated so use small bottles
            or drip bottles and clean the dripper with alcohol before and after use.)

    6)    Tin the tip of your iron with solder and wipe the tip off in the sponge that has been
            washed in distilled water (not tap water!!).  This will shock off the oxides and
            contaminates on the iron.

    7)    You can now proceed with soldering.  Turn on the fan and situate it so it will suck the
            fumes away from your face ( you should always use a fan when soldering or at the
            very least avoid the smoke!!).  Place the tip of the iron such that the sides of the
            iron touch the component lead and the pad at the same time.

    8)    Quickly touch the solder between the iron and the lead to aid in heat transfer.  Then
            proceed to the opposite side (solder will flow to the hottest point) of the component
            lead.  Draw the iron tip and solder up the component lead and off in a fluid action.
            This should take less than a second.

    9)    Clean the joint with the toothbrush and alcohol to remove flux.  If you did a proper
            job the component lead should seem to "flow" from the pad and the surface of the
            solder should be smooth.

    10)    The surface should reflect the light cleanly if you see any distortions such as cracks,
              rings or bubbles you should desolder the joint and redo it.  Trapped pockets of air
              can cause arcing which will carbonize the joint and component lead.

    11)    The same procedure can be applied to copper through holes except it is not
              necessary to bend the leads.

    12)    For IC's you should always have the leads bent so it fits easily through the holes
             without rubbing the sides.  When soldering do the alternate diagonals, then solder
             as shown below.

    Through Hole Desoldering:  You need to remove a through hole component from the PCB what now?? you have some options depending upon the type of board.

    Single Sided:
    1)    If the board is  single sided your best tool is to use solder-wik or chem-wik.  Buy
           only the wick that is pre-treated with dry flux (it works better) and use the proper
           width for the job.  Don't use wick that is as wide as a ribbon for small jobs ( it cools
           too quick).  Thin wick will fill to quickly with large gobs of solder.

    2)    To properly use wick place it between the iron and the lead, it will quickly draw the
            solder up keep the iron on the wick at all times don't let it cool.  Draw the wick up
            the lead and off, repeat as necessary.  As before with soldering be quick.

    3)    If you find you cannot get some solder to draw up the wick add a little bit of solder to
            the wick above the trouble spot.  This should help.

    4)    Using the popsicle stick straighten the lead and gently pull the component out.  If you
            meet any resistance don't force the lead out, apply some heat with the iron and it
            should come easily out.

     Double Sided:    With double sided board that have copper through the holes you can usually use the above method.  If this does not work then try the following method.

    1)    Clamp the PCB into a third-hand vise,  using the forceps grab onto one component
            lead and heat the underside with the iron.  Once the solder begins  to melt you
            should be able to ease the lead out of the board.  This should be a quick process if
            you are taking more than a few seconds stop add more solder to the under side
            to aid in heat transfer and proceed.

    2)    Once you have removed the component you will have a couple of filled holes.  You
            may be able to clean them out with the wick but you may be best to use a solder
            sucker.

    3)    "Cock" the sucker place it on the top side of the board while heating the solder.  When
            the solder melts "fire" the sucker and remove the iron and examine.  The hole should
            now be clean.  This is the method that will need to be done on double sided boards
            without through copper holes.

    4)    To remove an IC solder-wik is the best method.  However if the IC leads are making
            contact with the sides of the hole a more extreme approach may be needed.  You
            have to use side cutters and cut the body of the IC from its leads and then individually
            remove the leads using the soldering iron and forceps.  Use this as a last ditch since
            it destroys the chip.

    Surface Mount Soldering:     Like the saying goes " how do you get to Carnegy Hall?? Practice, Practice, Practice"  The same applies to surface mounts.  If you have coke bottle glasses and your hands shake more than a politician during an elections you may want to pass on this and let some one else do it.  However, if you are careful you can easily mount the larger lead IC's and surface mount resistors and capacitors.

    1)    The secret to surface mounting is heat, small tips, and flux, flux and more flux.  In
            addition, very thin solder ( it should be almost as thin as hair) should be used.

    2)    Clean the surface as in the procedure for through holes.  Apply flux to the pads
            and pre tin them (this layer should be very thin, flat and smooth).

    3)    Clean the surface with alcohol to remove any flux.  Add more flux and situate the
            component on the pads using a dental pick or something like one.  Add more flux.

    4)    If the component is only two leads you can hold it in place with the pick and
           solder one side then the other.  Otherwise, tack the corners then proceed as with
            the IC figure above.  Start on the lead if it is an IC and in one fluid motion slip down
            lead to the pad and off.

    5)    As with the through holes in the case of surface mount resistors and capacitors
            you should be able to distinguish the shape of the component flowing out of the joint.

    6)    For IC's you should not need to use more than a touch of solder.  The rule of thumb
            with good IC lead connections is that if you hold it at an angle to the light you should
            see a crescent reflection from the lead.

    Surface Mount Desoldering:    In removing surface mount components you have much more difficulty in not damaging the PCB or the component as the lead count increases.  So be sure its broken and not some lousy capacitor off to the side of the chip.
    Panasonic encountered this problem with their first run of GAOO Televisions in the 1990's.   In the spring after some TV were being returned for repairs under warranty that exhibited strange flaky problems.  They would turn on and off, change channels, activate menu commands and other stuff.  Many technicians immediately suspected the microprocessor chip which had over 100 pins.
    Chips were ordered an replaced but to no avail, it was later discovered that a ceramic capacitor responsible for key debouncing had bad  seals.  The end result was that when the air got moist they became large resistors and provided enough voltage to activate the microprocessor.
    So you really need to remove that surface mount??

    1)    For two lead components only.  Get two soldering irons pinch the resistor or what
           ever between them and lift it off.  Piece of cake.  now for the hard ones IC's.

    2)    To remove IC's you need a dental pick.  Heat and lightly pry each lead up so they
            are off the pad.  Use solder wick to clean up any leads that are still some what attached
            and remove the IC.  If you are careful you can reuse the chip.  There you go.

    I only recommend that you work on larger lead surface mounts and leave the smaller ones to people who are more skilled at it.
 
 

    Brainless Troubleshooting Tips:
    For the following please be very careful working on any energized circuit use an isolation transformer and always, always keep 1 hand in your pocket.  This is to prevent any cross heart shocks, even a 10 mA current can cause your heart to stop.

    Here are some tips to trouble-shooting circuits quickly with your common senses as an apprentice we were always told to look, listen, smell and touch (never taste).  The most common component that fails in any electrical circuit is electrolytic capacitors.  These components tend to dry out and are no longer capable of holding a charge.  If you have ever seen a TV with a Folded over image on the top of the screen 95 times out of 100 it will be a bad electrolytic in the vertical circuit.
    These are often easy to spot since they are "puffy" and often a different color due to the chemicals fading the labels.  I have often seen these capacitors missing a lead.  Since these capacitors are also used in power supplies and you notice a 60 cycle hum over some speakers this could indicate a bad filter capacitor.

    If something should start out OK and then slowly get worse you could have a thermal problem with a silicon device or capacitor.   Get a can of cold spray and test spray the circuit and see if you can locate the problem with the spray.

    If you experience momentary failures try lightly tapping the board with the end of the plastic end of the screw driver, or if its in a case lightly hit the case.  It the circuit reacts to this check for bad solder joints, look for cracks or carbon scoring.