GAME 101
Soldering
Soldering Introduction
• As the electronics industry matures in its
technology the methods of soldering
required for this technology has improved.
• Soldering is considered a scientific skill that
has to be taught to the technician/student
and then continually practiced.
Soldering Intro
• Engineers and technicians have found that many
failures that were attributed originally to faulty
components were actually the fault of poorly
soldered interconnections.
• Many studies have been done in the past to
determine what makes a good, strong and reliable
soldered connection.
• Decreased unit weight and increased reliability are
just two of the gains made from these studies.
Soldering Intro
• In today’s Armed Forces and in Industry, the
initial high cost of purchasing sophisticated
equipments severely limits the size of the buy and
the numbers of spares held "on shelf".
• Therefore, unplanned break-downs or failures are
costly; in time, money, delays or even lives.
• This is a cost too great to be taken lightly.
Soldering Intro
• Technicians must insure in all stages of
initial build, rework, modification or repair,
that sharp attention is paid to the making of
a strong and reliable soldered connection
and that all repairs are carried out to high
standards.
Fluxes
• Flux has other functions besides aiding the flow of
solder.
• One primary function is the removal of tarnishes
(light surface oxides).
• Under normal, everyday conditions both the
surfaces to be soldered and the solder itself have a
thin film of tarnish on their surfaces. This film,
which is made of oxides, sulphides, carbonates
and other corrosion producers, act as a barrier
interfering with the flow of solder.
• These tarnishes must be removed!
Flux
• When the flux is initially applied, the flux displaces the
gaseous layer from the metals surface;
• When the flux is then heated, the flux reacts chemically
with the tarnish, most often combining to form a third
compound which is either soluble in the flux or can be
carried away by the flux. This then exposes a clean metal
surface to the incoming solder.
NOTE:It is important to realize that these tarnishes cannot be
cleaned with any conventional solvent nor treated and
removed like a grease.
• The actual chemical reaction is one of corrosion. In the
flux's passive or raw state it should be non-conductive and
non-corrosive.
Flux
• When activated by heat, at slightly lower than
soldering temperature, the flux becomes very
corrosive.
• This insures a rapid rate of tarnish/oxide removal.
NOTE: Once the heat source is removed, the flux
cools down but still remains mildly corrosive.
Also since there are many impurities in the flux
residue, it is now somewhat conductive. Therefore,
it is mandatory that cleaning is carried out after
the soldering operation is complete.
Solder
• Today, as long ago, solder is made by combining
varying proportions of tin and lead.
• The most unique fact about this alloying is that the
hybrid alloy has a melting point always lower than
that of either the tin or lead alone.
• With most solder ratios, the melting point is not
sharply defined. It begins to melt at one
temperature but is not completely melted until a
higher temperature is reached.
Plastic State
• This intermediate stage is called the plastic
range or state.
• In this state the solder is neither a metal nor
completely liquid.
• The duration of the plastic range depends on
the ratio of solder elements being used.
Plastic range of 60/40 solder: melt begins at 361 degrees F
and is complete at 375 degrees F.
Solder Connection
• The actual solder joint is constructed only when
the solder is in the molten (liquid) state.
• When molten, the solder acts as a metal solvent.
• As it flows across the work piece, it dissolves a
tiny layer of the metal.
• This is called an intermetallic solution action or
intermetallic bonding.
• The solder dissolves and penetrates the metal's
surface with the molecules of both the solder and
metal combining to form a new metallic alloy
(SN6CU5).
• This bonding provides a continuous and
permanent bond that is also electrically constant.
Bonding / Wetting Action
• The degree or amount o£ bonding depends
on how much surface area is covered, or
how well the solder flows over the surface.
This action is called Wetting Action.
• Good wetting action can only occur when
the solder and work surface are at the
proper temperature and the work surface is
free from contamination.
Molten solder dissolves and penetrates a clean copper surface,
forming an intermetallic bond.
To insure proper wetting, the surface must be pre-cleaned.
Remove grease and oils with solvents;
Remove heavy oxides by abrading and pre-tinning; and
Flux component leads to prevent reoxidation.s
Dihedral Angle (Elevation)
• A visible indication whether or not a soldered
connection has the proper amount of wetting is the
dihedral angle.
• Dihedral is a term used to describe a positive or
upward elevation, like some aircraft wings.
• In soldering we use it to measure wetting action.
• A connection with a low dihedral angle is
considered to be the proper result of good cleaning
and wetting.
• In the figure below you can see on the left aide of
the component lead a very small dihedral angle,
less than 5 degrees. The right side has a far
greater dihedral angle.
Dihedral Angle
The preferred dihedral angle must be less than 30 degrees,
although standards of acceptability will allow for dihedrals up to
60 degrees. In any case anything over 60 degrees is unacceptable.
Soldering
• Correct soldering requires care, experience
and total attention to ensure high quality
results.
• It cannot be over-emphasized just how
important maintaining high soldering
standards is.
• With today’s greatly improved technology,
the individual component failure rate has
been reduced to a point where faulty solder
joint represents a significant percentage
of total failures.
Soldering Steps
The actual soldering process requires the use of
heat for three reasons:
a. to activate flux and convert solder to a liquid;
b. to decrease surface tension; and
c. to cause inter-metallic bonding to take place.
Contrary to popular thought, the real problem in
soldering is not controlling tip temperature but in
controlling the heat cycle of the work... how fast
the work gets hot .... how hot it gets... and how
long it stays hot.
Three Factors that must be
Considered when Soldering
• relative thermal mass,
• surface condition of the joint and
• thermal linkage.
Surface Condition of the Joint
• If there are any oxides or contaminants covering
the pads or leads there will then be a
barrier/blockage to the flow of heat between the
pad/lead and iron tip. The end result being, the tip
is unable to supply enough heat to melt the solder.
• To make a good solder joint, the surface must be
clean!!!
• Before attempting to solder, clean the joint with a
solvent, such as Freon TF, to remove greases and
other films. Then use a fine-abrasive to remove
the surface oxides.
• NOTE: Do not use an abrasive on gold plated
leads as the base metal may not be solderable.
The Technician’s Job
How can the technician tell when there is
too much or too-little-heat being applied to
the workplace? We use the (W.P.I.) Work
Piece Indicator which is defined as:
• The reaction of the workpiece to the work
actions being performed on it, and are
discernible to the human senses of SIGHT,
TOUCH, SMELL, and SOUND.
Work Piece Indicators
• In other words, we use a method of observation
using your senses while performing an action. Then
seeing the effect and modifying your action as a
result of the effect.
• Work can be viewed as a closed-loop system;
feed-back comes from the reaction of the
workpiece and is used to modify the action.
Workpiece Indicators - changes discernible to the human
senses - are the way "the work talks back to you"
Workpiece Indicators
Soldering and De-soldering
• For soldering and de-soldering the most important
workpiece indicator is heat rate recognition. In
other words, observing the rate at which the entire
solder joint melts. This rate is determined by:
a. capacity of the iron;
b. surface condition of the tip;
c. thermal linkage between tip and workpiece;
d. surface condition of the work piece; and
e. relative thermal mass of tip and workpiece.
Workpiece Indicators
• Another workpiece indicator is the change
in workpiece colour and brightness although
this W.P.I. is used more at a later stage.
Soldering Iron
• When applying the soldering iron to the workpiece,
the tip should be applied to the point of maximum
mass.
• The tip must make maximum contact at this point
to ensure a rapid rate of temperature elevation to
the soldering temperature.
• This is done by building a heat bridge. This would
help to lessen the chance of heat damage to heatsensitive components.
Soldering Iron
• Before applying solder to the joint, the
temperature of the workpiece must be higher than
the solder's melting point.
• When this is done and the workpiece is properly
cleaned and fluxed, the solder will melt and flow
without direct contact to the iron, resulting in a
smooth, even surface that feathers out at the edge
(low dihedral angle).
• Do not apply the solder to the soldering iron tip
and allow it to flow to the cooler workpiece
surface as this will result in an improperly wetted
joint or spikes.
CONSTRUCTION OF THE
SOLDER JOINT
• Before the actual soldering is to take place,
let's look at what makes a soldered
connection acceptable or not.
• Acceptable solder joints should consist of a
well feathered, shiny, continuous fillet
without gap or fracture, with the two
soldered surfaces plainly visible through the
fillet.
A good solder joint
- is clean
- is bright
- is shiny
- has a concave fillet
- has good wetting
An unacceptable solder joint can be:
- pregnant
- lean
- pitted
- spiked
- outgassed
- frosty
- fractured
- balled (solder balls)
- re-melted
- has poor wetting
- has copper showing
SINGLE STEP METHOD
a.
b.
c.
d.
Remove all greases/grimes with a suitable solvent.
Remove any heavy oxides/tarnishes by abrasive means.
Clean all abrading residues with a suitable solvent.
Flux all exposed areas and work surfaces (controls new oxide build-up)
when working with wire leads; flux and pre-tin.
e. Ensure soldering iron is at correct operating temperature,
f. Clean tip and thermal shock the tip to remove oxides.
g. Place tip at point of maximum mass and build a heat bridge.
h. Remove solder and allow joint to heat.
i. Place solder farthest away from heat source (usually opposite to the
iron or on top of the lead).
j. Remove solder.
k. Remove iron.
l. Thoroughly clean all flux residues and cleaning agent residues from
workpiece.
m. Check for acceptability of finished joint.
NOTE: Total dwell time should not exceed 3 sec for discrete
components and 2 sec for semi-conductor devices!!