Electronic Products Assembly and servicing

1. Soldering and Desoldering
Electronic Components
Unit Code: TLE_IAEPAS9-12AEP-IVc-f-29
Competency: ASSEMBLING ELECTRONIC PRODUCTS (AEP)
Trainer: G-one T. Paisones
TVL Head: Marita C. Gumanit, Ph.D.

2. Learning Competency/Objectives
 LO 3. Mount and solder electronic components
3.1 Apply knowledge on lead and lead-free soldering
characteristics and requirements in mounting and
soldering process in accordance with OHS standards
3.2 Mount and solder components in accordance with
soldering principles
3.3 Apply soldering/desoldering techniques and
procedures in accordance with established standards
and requirements
3.4 Check soldered products in accordance with
international standards and task specifications
 TLE_IAEPAS9-12AEP-IVc-f-29

3. How to Solder Electronics
Learning to solder through-hole
components is an essential skill for
any amateur hobbyist or electronic
professional. You can learn what
equipment and skills you'll need to get
started soldering electronics properly.

4. Getting the Necessary Equipment
Use a soldering iron with the appropriate heat
control
For soldering electrical components into printed
circuit boards, the best soldering irons are
Electrostatic Discharge (ESD) safe, temperature-
controlled, high-power irons. These will let you
solder for hours, and are good for complex
amateur radio projects. For simple kits, an
inexpensive pencil iron will do just fine.
Use a fixed power soldering iron, 25-watt for
small jobs and 100-watt for larger jobs with
heavy cabling.
If possible, variable temperature irons are
available, which will make for the safest
treatment of the boards. The tip temperature can
be controlled to suit the size of the job.

5. Solder Wire Use solder wire of an appropriate alloy
The most common solder alloy used in
electronics is 60% tin and 40% lead, sometimes
termed 60/40(SN/Pb); the lowest melting
temperature is actually 63/37. This is
recommended if you are new to soldering,
though because of the lead content it is
somewhat hazardous. You must use proper
ventilation (or a proper respiratory mask), or
soldering equipment with a vacuum attachment.
Solder that is 60/40 becomes pliable at 361 °F
(183 °C) but doesn’t melt until it’s 370 °F
(188 °C), which means it may be difficult to
work with if you’re a beginner. Instead you can
try solder that’s 63/37 since it melts at 361 °F
(183 °C).

6. Use solder wire of an appropriate alloy
 Various lead-free alloys are becoming necessary in recent
years under the RoHS regulatory initiative. These require
higher soldering temperatures and do not "wet" as well as
tin-lead alloys. While they are safer, they are also more
confusing. The most common is 96.5% tin to 3.5% silver
and will produce a joint with less electrical resistance than
a tin-lead alloy. In practice, this is not a reason to use it;
the safety issue is the driving factor. You can also get
solder that is almost 100% tin, but it is more expensive.
 Both lead and lead-free formulations are available online
at places like solderdirect.com and in various stores in
most localities.

7. Flux  Use a flux-cored solder wire for
electrical work. Make certain the flux
used is electrically
compatible. Plumbing solder flux is
most definitely not. Flux is a material
(rosin or a variation for electrical work)
used to prepare surfaces for soldering.
Dirt, grease, and so on will interfere
with the solder joint and must be
removed. Including the flux within the
solder wire automatically supplies flux
to the surfaces being soldered and is
the most sensible choice, though very
small, surface mounts or automated
soldering may use alternatives.

8. Use a flux-cored solder wire for electrical
work
 There are several different fluxes commonly available for electrical/electronic
work. In order of popularity, these are RMA, RA, and water-soluble fluxes.[4] The
more active a flux is, the more important it is that it not remain after soldering, lest
continuing chemical action compromise or damage the operation of the electrical
or electronic equipment. In particular, water-soluble fluxes must be removed.
 After soldering, rosins leave a brown, sticky residue which is ideally, non-
corrosive and non-conductive. Cleaning can be accomplished with a purpose-
formulated rosin removal product, or with isopropyl alcohol.
 No-clean flux leaves a clear residue after soldering, which is non-corrosive and
non-conductive. This flux is designed to be left on the solder joint and
surrounding areas.
 Water-soluble flux usually has a higher activity that leaves a residue which must
be cleaned with water. The residue is corrosive and may also damage the board
or components if not cleaned correctly after use.

9. Printed Circuit Board
 Get the necessary board and components. Mostly,
electrical soldering deals with "through-hole" components,
whose leads are inserted into holes in printed circuit
boards (PCBs) and soldered to a pad of metal plating (a
PCB trace) around the hole. The interior of the hole may
be "plated through" or not; in the latter case the inserted
lead is the electrical connection between traces on the top
and bottom of the PCB. Soldering the lead on both sides
will commonly be necessary in the last case.
 Soldering other electrical items, such as wires or lugs, has
slightly different techniques, but the general principles of
operating the solder and iron are the same. Note however,
the lugs and other unsupported soldering points require a
firm mechanical connection prior to soldering. A solder
joint does NOT provide mechanical strength or resistance
to vibration; it only provides a very low resistance
electrical connection.

10. Clamp
Get a clamp to hold the components
 Electrical components are usually quite
small, and you'll need tongs, needle-
nosed pliers, or tweezers to hold them
in place while you operate the
soldering iron and negotiate the solder.
It can be a balancing act.
 Some kind of clamp or stand is usually
best to hold the board in place while
you solder the components.

11. Soldering the Components
Prepare the components for
soldering
 Select the correct component by
checking its type and value
carefully. With resistors, check
their color code. Bend leads
correctly, if necessary, being
careful not to exceed the stress
specs (eg, by too sharp a bend),
and clinch leads to fit the board.

12. Be extremely careful and solder only in
an appropriate environment
 Always solder in a well-ventilated area,
using breathing and eye protection.
Make sure to safely place the iron
(using a fireproof stand or holder) when
it is on but not in use. Irons can start
fires quite easily by burning into your
workbench or paper or plastic. Always
use a thermal mat or board to protect
the area.
 Leave 7–12 inches (18–30 cm) of
space between the electronic
components and your face, or solder
bits or hot flux may reach your eyes.
Safety spectacles are a very sensible
precaution. Molten solder may splatter,
and is essentially unpredictable.

13. "Tin" the soldering iron tip
Melt a small blob of solder on end of
the soldering iron. This process is
called tinning and it helps to improve
heat flow from the iron to the lead
and pad, keeping the board safe
from prolonged heat.
Carefully place the tip (with the blob)
onto the interface of the lead and
pad. The tip or blob must touch both
the lead and the pad.
The tip of the soldering iron should
not be touching the nonmetallic area
of the PCB, whether fibreglass (very
common) or some other material.
This area can be damaged by

14. Feed the solder wire onto the interface
between the pad and lead
Flux from the solder wire is only active very briefly
maximum after melting onto the joint. It is burned off
slowly (this is the smoke rising from the joint) and
loses its effectiveness as it does so. The component
lead and the pad should be heated enough for the
solder to melt into the connection point. The molten
solder should "cling" to the pad and lead together via
surface tension. This is commonly referred to as
wetting.
If the solder does not melt onto the area, the most
likely cause is insufficient heat has been transferred to
it, or the surface needs to be cleaned of grease or dirt.
The activity of the flux was not sufficient, and external
flux may be necessary. Careful cleaning of surfaces
prior to soldering may be needed.
Use care—sandpaper will generally be too harsh and
steel wool (though less mechanically harsh) will add
tiny bits of conductive metal—probably leading to
unintended shorts and electrical misbehavior.

15. Stop feeding new solder when all the
surfaces have been wetted
When the gaps are filled and the surfaces
are wet, you should stop adding more solder.
No more than a drop or two of solder should
be necessary for most joints, though it will
vary slightly for different components. The
correct amount of solder is determined by:
On plated-PCBs, you should stop feeding
when a solid concave fillet can be seen
around the joint.
On non-plated PCBs, you want to stop
feeding when the solder forms a flat fillet.
Too much solder will form a bulbous joint with
a convex shape (ie, blob-like), while too little
solder will form an irregular concave joint.
Both are visual indications that the solder
joint is defective.

16. Soldering Well
 Move quickly. Unfortunately, it's quite easy
to damage a component or the board with
too much heat. For the most part, however,
you can keep the components and the
board safe by moving swiftly. A finger on the
board nearby may help to notice too much
heat.
 Try to err on the side of irons that are less
powerful than you think you might need. A
30-watt iron will be adequate for most
electronic work. Practice soldering is a very
good idea.
 If working with a double-sided circuit board
check both sides for good solder joints. A
good joint will look shiny and cone-shaped.
if it looks frosty and dull then it is likely a

17. Consider using heat sinks to protect
sensitive components
 Some components (diodes,
transistors, etc.) are quite
susceptible to heat damage and
require a small aluminum heat-
sink clipped on to their leads on
the opposite side of the PCB.
Small aluminum heat sinks can be
purchased through electronics
supply houses. Hemostats (small)
can also be used.

18. Learn to recognize when there is enough
solder present
 After a proper application of solder, the
solder will be shiny and not dull. Visible
indications are the best way to know if
your solder joint is good. The solder
must melt onto the surface of the
electronic components or PCB traces,
rather than the tip of the soldering iron.
This way, when the solder cools, it
forms a close connection to the
surface of the metal.
 The solder joint should coat the
surface of the component evenly, not
too much such that it forms a glob, nor
too little such that it does not

19. Keep the soldering iron clean
 Burnt flux, rosin from the core of the
solder, or plastic sheaths from wires
may all contaminate the soldering iron
tip. Such contaminants prevent the
formation of a proper bond between the
electronic components. This is
undesirable because it raises the
electrical resistance and also reduces
the mechanical strength of the solder
joint. A clean tip is shiny all the way
around, without burnt gunk on it.
 Clean the iron in between each
component that you solder. Use a damp
sponge or bronze (or brass) wool to
clean it thoroughly

20. Let the solder cool completely before
moving the components
 Solder remains soft for a time, and there is
little visual indication when the mushy phase
ends. This cooling should only a few
seconds in most electronic situations; large
components have more mass and are both
harder to heat sufficiently to solder them and
also take much longer to cool to solidify.
 If the components are too hot to handle, use
needle nose pliers, or a tool called helping
hands which consists of two alligator clips
attached to a little articulated stand. If you
watch carefully, the cooling solder will settle
right before your eyes.

21. Practice on junk components
 It's important to practice on throwaway
stuff before you move straight to trying
to solder something important. Get
some junk components from an old
radio or some such to practice on.
 Nobody is perfect, not even the
professionals. Don't be ashamed to
repeat a bit of soldering work (it's
officially called rework in the business).
It will save you time in troubleshooting
later.

22. Tips
 The tip of a soldering iron tends to get stuck with time (if
frequently used), due to oxides that build up between the
copper tip and the iron sleeve. Plated tips do not usually have
this problem. If the copper tip is not removed now and then, it
will get stuck permanently in the soldering iron! It is then
destroyed. Therefore: every 20 - 50 or so hours of use, when
cold, remove the tip and move it back and forth and around so
the oxide scales can come out, before locking it in place
again! Now you soldering iron will last for many years of use!
 Keep handy a rubber-bulb or other suction de-solderer (sucks
up melted solder) or a spool of desoldering braid (fine copper
mesh that absorbs melted solder) in case you mess up and
need to disconnect something or remove excess solder from
a joint.

23. Tips
 Also if you have it on hand, when the iron is cold, use a
wire brush (brass is best) to work on the scale and
oxides. Only recommended every 60-75 hours of use.
 Most soldering irons have replaceable tips. Soldering
iron tips have a limited working life and also are
available in different types of shapes and sizes, to suit a
variety of jobs.
 If you should accidentally burn yourself with the
soldering iron, rinse the burn with tap water for 15
minutes. The burnt area will create a boil, but don't
worry, it will heal within 3 to 4 weeks. If the condition
persists, go to the clinic and consult with the doctor.

24. Warnings
 Soldering irons are very hot. Do not touch the tip
with your skin. Also, always use a suitable stand or
holder to keep the tip up and off of your work
surface.
 Solders, especially lead-based solders, contain
hazardous materials. Wash your hands after
soldering, and be aware that items containing solder
may require special handling if you dispose of them.
 Use a thermal mat or board to protect your
workspace from burns or possible fires.