DVD-18C Soldering Terminals - IPC

Humor Opening
DVD-18C Transcript
DVD-18C
Soldering Terminals
Below is a copy of the narration for DVD-18C. The contents for
this script were developed by a review group of industry experts and
were based on the best available knowledge at the time of
development. The narration may be helpful for translation and
technical reference.
Copyright © IPC – Association Connecting Electronics Industries. All Rights Reserved.
Operator: (Surprised) Hey, Doctor Solder! You making house calls now?
Doctor S: Afraid I’ve got some bad news, Johnny.
Operator: (Shocked) What is it? Give it to me straight, doc.
Doctor S: Your terminal...
Operator (Interrupting, stunned): Oh, no... I’m terminal... how long have I got?
Doctor S: No, you idiot. Your solder on this terminal is abominable! And I don’t like saying it,
either – probably cause it’s so hard. (Pauses, concentrates.) “Terminal... Abominable.” Hey, I
did it again. (Pleased with himself.)
Operator: Oh no, I feel terrible about this.
Doctor S: That’s okay... I know a good remedy!
Operator: What? I’ll try anything...
Doctor S: Well, sit up straight, stop your moping, and watch this... somebody, get the popcorn.
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Introduction
DVD-18C Transcript
This video will demonstrate the techniques for hand soldering wires to a variety of terminals. For
our discussion, a terminal is a metallic connection device that is used to terminate a discrete wire,
or wires. The terminal provides both a mechanical and an electrical connection.
There are several different types of terminals – each requiring specific hand soldering techniques.
We'll be examining turret terminals, cup terminals, bifurcated terminals, hook terminals and
pierced terminals. For an overview of the tools and materials required for basic hand soldering of
through hole components to printed circuit boards – as well as safety and handling considerations,
refer to IPC videos DVD-42C for tin lead soldering and DVD-43C for lead free soldering.
A hand soldering iron with interchangeable tips will be used for soldering terminals. There are
conical tips and chisel tips. Conical tips are round and chisel tips are flat. We'll be using chisel
tips because they have a flat edge. A chisel tip with a flat surface has a much greater contact area
than a conical tip – and therefore transfers heat more efficiently.
The first step is to tin the tip of the iron. Tinning will reduce the formation of oxides on the
soldering iron tip. Oxidation acts as a barrier or an insulator – meaning it slows down the
transfer of heat. It may also prevent wetting of the surfaces with fresh solder. Tinning the tip
with solder also results in faster heat transfer.
The insulated wire also needs to be stripped and tinned prior to attachment to the terminal. There
are many ways to strip the insulated wire. Some methods are unacceptable because of possible
damage to the insulation and the wire. The safest method uses the thermal stripper – which melts
or softens the insulation. Use your fingers to twist the insulation slug off in the direction of the
wire lay. Do not use the stripper to pull off the insulation slug as it can potentially damage the
wire. The main disadvantage of thermal strippers is that some insulation, such as PVC, will burn
and release hazardous gasses when melted. If you’re not sure which types of insulation are
appropriate for thermal stripping, be sure to ask your supervisor.
The stripped wire now needs to be tinned. The purpose of tinning is to avoid damage to the
individual strands when the wire is bent – and to improve solderability. To tin the wire, you can
move it across a solder coated iron tip, move a tinned tip over a stationary wire, or dip it in a
solder pot.
Before we begin soldering terminals it’s important to clean the soldering iron tip. This can be
done by wiping the tip on a slightly damp, sulfur free sponge – or dabbing it on a brass pad made
specifically for hand soldering.
Turret Terminals
We’ll start with the turret terminal. The tinned end of the wire is first formed into a loop since
the wire will need to be wrapped around the terminal. The loop is then cut to fit the terminal.
The wire end should not extend off the base of the terminal by more than one lead diameter.
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DVD-18C Transcript
When forming the wire, you should use a tool that does not leave marks or impressions on the
conductor – such as round nose pliers. The loop you make with the wire should curve like a
semi-circle. An angled loop is not acceptable.
Now the wire can be placed in position on the turret terminal. You know you have made a good
loop when it snaps into place and wants to stay on the terminal even without any solder.
There can be different degrees of termination of the wire wraps. For example, 180 degrees is half
way around the terminal and 360 degrees is all the way around, or one complete turn. Your
acceptance requirements may be based on your company’s specification, or IPC standards. For
example, IPC-A-610 specifies that a wire diameter of 28 AWG or larger – built to class 3
requirements – should wrap 180 to 360 degrees. A 30 AWG wire diameter or smaller – built to
class 3 – should be wrapped more than one complete turn.
During the soldering process nothing – except for the technician’s hands – should move. This
will eliminate the risk of disturbed solder. The terminal should be mounted securely – and the
non-soldered wire end should be held by a third hand tool, or equivalent.
In the case of our turret terminal, if one wire is to be connected, it should be placed on the lower
section of the terminal. It should lay flat against the base so that any mechanical stress will be
transferred to the board rather than tilting the terminal and perhaps damaging the land. Another
benefit of mounting the wire on the base is that the wire actually ends up against a corner between
the base and the post. After creating top and bottom solder fillets, there will be a very strong
mechanical connection. The turret manufacturers loved this idea so much, they gave you two
bases to work with.
With two wires, they should both be brought in from the same side so that the insulations touch.
This will leave a gap between the stripped areas of the wires. The gap makes it easier to inspect
the solder joint, and allows for the two parallel wires to be joined with tie wraps or lacing.
Now let's take a look at the proper technique for soldering turret terminals. The soldering
operation consists of four basic steps. In step 1, the solder wire is placed in contact with the
wrapped wire and the terminal. This is the point of greatest thermal mass and is called the
"contact point." This contact point will help to transfer the heat to both the wire and the terminal
simultaneously. The soldering iron tip is brought into the contact point – melting the solder wire
– thus forming a solder heat bridge. The purpose of the solder heat bridge is to transfer heat
more rapidly to the solder fillet area and to preheat the wire and terminal so they are hot enough
to melt solder.
During step 2, additional solder is applied on the opposite side of the contact point to form the
necessary solder fillet. You will know you made a good heat bridge if the solder melts rapidly
when it contacts the wire or the terminal.
In step 3, the solder wire is removed. In the final step, the iron is withdrawn at the same angle it
was introduced into the joint.
Notice that the iron was inserted at one location, held still to transfer maximum heat, and then
removed. The iron should not be moved up and down – making multiple contacts. It’s
appropriate to think of the soldering iron as a heat source – not a paint brush. Let’s watch the
entire operation once again in real time.
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DVD-18C Transcript
Another method of forming a solder heat bridge is to first place the soldering iron tip in contact
with the wire and the terminal – and then add a small amount of solder to the contact point.
Again, additional solder is applied on the opposite side of the contact point to form the necessary
solder fillet.
At this point, we'll remove the flux to inspect the joint. The cleaning requirements are the same
as any other hand solder connections on a circuit board. Some companies use low residue or noclean
fluxes which may not require cleaning. Other fluxes can cause corrosion or contribute to
dendritic growth. These residues will need to be cleaned off. It is important to adhere to the
manufacturer's specification for solder temperature and cleaning requirements. Your company
will supply you with a compatible cleaning solvent and instructions for its use. They will make
the decision whether to clean or not based on customer requirements for reliability or cosmetic
quality.
Once the flux is cleaned, we’re ready to inspect the solder joint. Do you know how to determine
the correct amount of solder? What exactly do you look for when examining a solder joint?
IPC-A-610, J-STD-001 and IPC-A-620 all provide acceptance criteria for soldering terminals.
Check that the solder is feathered out smoothly – showing good wetting action over the wire and
the terminal. Wetting is the adhesion of a smooth, unbroken film of solder onto a base metal.
The outline of the wire should be visible under a thin film of solder. This connection location is
called a fillet. On a proper solder joint, the solder fillet is slightly concave, or curved inward. A
concave fillet that tapers to a feathered edge not only looks good, but also reassures us that the
solder bonded to the two surfaces we were trying to join.
When there is insufficient solder, the joint may not have acceptable mechanical strength. When
there is excessive solder, the fillet will be convex and the outline of the wire will be buried in the
mound of solder. This is undesirable because the excess solder can hide defects in the
connection.
It is important to solder so that the joint can be visually inspected. Soldering for inspectability
means you're always able to see the outline of the wire in the joint. When excess solder is
evident, the outline of the wire will not be visible.
Cup Terminals
The next type of terminal we’ll discuss is the cup terminal. The cup part is a hollow cylinder.
The wire will be inserted into the cup and then soldered. During any soldering process nothing
except the technician’s hands should move. This will eliminate the risk of disturbed solder. The
terminal needs to be mounted securely – and the non-soldered wire end should be held by a third-
hand tool, or equivalent.
The wire size must be matched to the terminal. Never modify the wire or the terminal to make the
wire fit. Several smaller wires may be placed into a single cup – as long as the wires do not
exceed the diameter of the cup. It is not acceptable to twist multiple wires together before
inserting them. The twisted wires may trap flux inside and may also change the acceptable
diameter of the wires that are inserted.
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DVD-18C Transcript
Now let’s examine the steps to properly solder wires in cup terminals. First, insert the pre-tinned
wire into the cup to measure for correct wire length and insulation clearance. For minimum
insulation clearance, the insulation may contact the top of the cup, but not interfere with the
solder wetting to the inside of the cup terminal. Maximum insulation clearance should be less
than two wire insulation diameters, or 1.5 millimeters whichever is larger. As you can see, the
insulation clearance in this example is excessive and should be corrected before we solder this
connection.
Now, we’ll place the properly stripped and pre-tinned wire into the cup – and secure the wire
using a third hand tool, or equivalent. The conductor should be fully inserted into the cup –
touching the back wall for its full length. Next, we’ll place a large, clean chisel tip against the
back of the cup to transfer heat into the terminal. Then we’ll insert the solder wire into the cup
opening – against the back wall to form a small fillet between the back wall and the wire.
In the final step, we’ll move the solder wire to the center to avoid touching the left or right edges
–minimizing the chance of spilling over as the cup fills with solder. The solder wire and
soldering iron tip are then removed from the cup at the same time. It’s important to leave
everything still until the solder solidifies.
If excessive solder is used, it will spill down the sides of the cup. If insufficient solder is used, the
solder connection won’t have the required mechanical strength.
At this point, we’ll clean off the flux – if required. Here is what the acceptable solder joint will
look like. The wire is fully in the cup and there is an insulation clearance from the top of the cup
to the insulation of the wire. The solder contains no dips or recesses within it, and hasn't spilled
over and down the sides of the cup. Also, check that there is no buildup of solder on the cup
where the soldering iron made contact. If there is a small quantity of external solder, it should be
a smooth film with no bumps. When the solder volume is correct, the fillets are slightly concave
and show good wetting on all the surfaces. Unlike the other terminals, the outline of the
conductor is not required to be visible inside the cup.
When there is insufficient solder, the connection may not have acceptable mechanical strength.
When excessive solder is used, solder buildup on the outside of the cup may negatively affect the
form, fit, function or reliability.
In situations where the cup terminal is inside a connector, the soldering operation is much more
difficult. The area you'll be working in is considerably smaller and there is the danger of possibly
burning or damaging adjacent wires. In this case, a resistance soldering tool can be useful. This
tool contains a pair of electrodes that can grip the cup and send electrical current through it. The
current will heat up the metal and melt the solder. The manual for the resistance soldering tool
will specify the correct setting based upon the type of terminal you're soldering. The advantage of
this tool is that the electrodes can be positioned before the heat is turned on. That means you
won’t accidentally heat the wrong area and possibly cause damage. The cup containing the solder
is gripped with firm pressure and a foot switch is depressed to start the heat.
Insert the wire – press the foot pedal – and feed in the solder. Then release the foot switch. After
solder solidification, remove the electrodes. The foot switch should always be released before the
electrodes are removed to prevent arcing. Electrical arcing could damage the plating on the
terminal.
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Bifurcated Terminals
DVD-18C Transcript
Now let's take a look at bifurcated, or forked terminals. On these terminals, the wires can enter
from the side, the top, or the bottom. Side entry is commonly used when one or more wires are
connected. The recommended minimum wrap on a bifurcated terminal is 90 degrees. 180 degrees
is used when additional mechanical strength is desired, and when there is sufficient clearance
between adjacent terminals. When two or more wires are required, they should be wrapped to
alternating posts.
Let's watch the soldering operation for a side route installation of one wire. The pre-tinned wire
is laid across the terminals to determine the proper insulation clearance. A 180 degree wrap is
made using a pliers that won’t cause damage to the wire. The wire is now positioned and
trimmed so that it doesn't protrude more than one conductor diameter beyond the edge of the
terminal. We do this to make sure the conductor doesn’t violate electrical clearance and cause a
short circuit. The wire should be mounted at the bottom of the slot – between the terminal posts.
Now, place the solder wire in contact with the terminal base and the wrapped wire.
Next, a solder heat bridge is made. Remember, the purpose of the heat bridge is to transfer the
heat more quickly to the connection and to preheat both the wire and terminal so they are hot
enough to melt the solder. Then the solder is touched to the other side to form a proper solder
fillet. After the right amount of solder is melted, remove the solder wire – followed by the iron.
Let’s watch these steps once again – in real time.
The joint can now be cleaned – if required. The acceptable joint will have a concave fillet
between the wire and the terminal. It should be smooth, clean, and display evidence of wetting. It
is recommended that the wire should be in contact with all three terminal post surfaces. Here’s
another joint that has insufficient solder and may not have acceptable mechanical strength. Also,
notice that the wire is extending beyond the edge of the terminal more than one lead diameter –
which is not acceptable. This joint has excessive solder. The fillet bulges out and the outline of
the wire is covered by the excess solder.
In addition to side entry, wires may also enter from the top or bottom. For top entry of bifurcated
terminals, the tinned wire may be bent to double thickness – thereby contacting more surfaces for
a stronger connection. Once properly inserted, the wire is soldered. If the wire is too large for
double thickness, a filler wire is cut to length and added to fill the space. For bottom entry, the
wire is bent a minimum of 90 degrees from where it comes up through the hole. The wire should
then be trimmed so it doesn't protrude more than one wire diameter beyond the edge of the
terminal. Make sure the wire insulation does not enter the hollow terminal.
Hook Terminals
Next, we’ll look at hook terminals. Hook terminals are found primarily on hermetically sealed
relays. The wire wrap should be at least 180 degrees. Numerous tools can be used to make the
wrap for hook terminals as long as they don’t nick, scrape or leave impressions on the conductor.
One example that we’ll use here is round nosed pliers.
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DVD-18C Transcript
Now let's examine how hook terminals are soldered. Once the wire is pre-tinned, formed, and
attached to the terminal – and held in place with a third hand tool – the solder wire is placed in
contact with the terminal and the wrapped wire. Next, a solder heat bridge is formed. Then the
solder is moved to the opposite side of the fillet area. After the solder flows over the wire to form
the proper fillet, the solder wire is removed. Then the iron is withdrawn at the same angle it was
introduced to the joint. Last, we clean off all flux – if required.
The acceptable solder joint will have the same characteristics we've seen so far – slightly concave
fillets and evidence of good wetting. Here are two unacceptable solder joints – with insufficient
solder and excessive solder.
Pierced Terminals
The last terminal we'll be soldering is the pierced terminal. Pierced terminals have a hole in the
middle. The hole may be a circular, oval or square. Wire can enter from either side, or from the
top. The pre-tinned wire should be mounted through the hole, then wrapped and positioned to
contact both the flat sides of the terminal – and held with a third hand tool.
Let's watch the proper soldering operation for pierced terminals. Notice that it's the same basic
procedure we've seen for many of the terminals. Remember the four basic steps of the soldering
operation.
The solder wire is placed at the point of greatest thermal mass – in contact with the terminal and
the wrapped wire. Additional solder is then applied on the opposite side of the contact point to
form the necessary solder fillet. The solder wire is removed when a sufficient amount of solder
has been added to the joint. Finally, the iron is withdrawn at the same angle it was introduced to
the joint. Then the flux is cleaned off – if required.
The target joint will have a concave fillet between the wire and the terminal. It is not necessary to
fill the hole of a pierced terminal with solder. The solder fillet only needs to be between the wire
and the flat surfaces of the terminal. It should be smooth, clean, and display evidence of wetting.
When there is insufficient solder, the joint may not have acceptable mechanical strength. When
there is excessive solder, the fillet will be convex and the outline of the wire will be buried in the
mound of solder. This is undesirable because the excess solder can hide defects in the
connection.
Summary
As you've seen, there are many different types of terminals and wire positioning arrangements –
but the same soldering procedures apply to all. We’ve shown the methods for soldering turret
terminals...cup terminals...bifurcated terminals...hook terminals...and pierced terminals.
Terminals are part of our everyday lives. When we turn on our electronic products, we are
relying on someone’s careful assembly of wires to terminals somewhere inside the chassis. It’s
important to always do our best quality work.
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DVD-18C Transcript
And take it from Dr. Solder -- you never know whose life and livelihood may be depending on
us. Now, make two solder joints and call me in the morning.
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