12 Flexible Printed Circuit Boards
13.7 Other Hand Soldering Tools
The soldering workstation should be clean, ESD-controlled and organized for an easy access to all the tools. The typical tools may include:
a Solder iron;
a Cleaning material;
a Cored solder;
a Pliers (bent, nose and straight);
a Wire stripper;
a Lead forming tools;
a Toolbox a Fume absorber;
a Solder iron station including holder;
a Set of soldering iron bits;
a Flux; sponge; soldering braid;
a Tweezers;
a Wire cutter;
25 50 75 100 125 150 175
200 Risk of thermal damage
Risk of coldjoints
Time
°C
Ideal for soldering
Fig. 13.8 Ideal temperature range for soldering
Soldering, Assembly and Re-working Techniques 473
Fig. 13.9 Side cutter B
ED
B C
A B
Overall length Jaw length Jaw width Jaw thickness Knife length Point thickness C
D E F D
F
Diagonal cutting plier E
C D
Side cutting plier End cutting plier
A A
A B
C
a Screwdriver set;
a Board holder; and
a Cleaning solvent and brush.
13.7.1 Cutters
Good cutters are an essential tool for component lead cutting and removing insulation prior to soldering or performing. Ideally, they should be of the side cutter type with insulated grips. They should be slimline and lightweight for precision work. Cutters up to 35 cm long are employed in electronics applications. The cutters should be made of high quality tool steel so that they will make a sharp, clean cut. The tips of the cutters should be tapered to allow the user to reach a particular wire in a crowded area. Cutter jaws should be every well aigned so that cutting edges meet squarely and allow little or no light to pass through when held together. Cutter action should be smooth and clean.
Cutters should be used only for cutting copper wire or leads and not for trimming PCBs or metal parts. The cutting blades are easily blunted if misused. A blunt pair of cutter is worse than useless as it will not crop leads cleanly or strip insulation from wire without snagging and breaking strands.
Some cutters have a safety clip incorporated, which traps the cut-off lead and stops it from flying and ending up all over the room.
Sometimes, it is difficult to strip the wire with the cutters. In that case, one can use wire strippers and cutters, which are available with adjustable stops for different wire sizes. The stop ensures that the cutting action is limited to the thickness of the insulation and will prevent nicking the actual wire.
Cutters are specified to cut wires up to a specific diameter and material, usually in electronics, out of copper. One should not try to cut anything larger than the specified sizes in order to avoid damage to the cutting edges. As a rule of thumb, most of the small cutters cut up to 1mm copper wire without any damage.
There are different types of cutters available but, in essence, they have variations only in the cutting portions.
The cutting portion must be sharp, straight and without any impressions along the edges. After a period of use when the edges of the cutter become blunt, they can be either re-sharpened or replaced. There are two basic variations in the shape of the cutting edge are shown in Figure 13.9:
a Flush Cutter: Flush cutters are made to cut soft wires like silver, gold, copper etc. and should not be used to cut heavy hardened wires like steel wires. The cutting edge that cut the wire produces a straight face to one side of the wire.
a Diagonal Cutter: These cutters are pretty durable and work well on most wires. They make V-Shapes to the wire end.
13.7.2 Pliers
One of the most commonly used tools in electronics shops are pliers. The frequent tasks for which pliers are used include holding wires in place during soldering, acting as a heat sink to protect a delicate component, bending component leads to fit mounting holes on a circuit board and pulling wires through a panel or chassis hole.
Obviously, one single design in pliers cannot meet all the demands. Therefore, there are many types of pliers. The important types are shown in Figure 13.10. Some pliers also have cutting knives. A single pair of long nose pliers is adequate for most jobs, but having several on hand can simplify a task.
F
D D
E
B E
C C
B
A Slipjoint plier Curved nose plier Long nose plier
Flat nose and duck bill plier A
D F
E B
A C
A B
Overall length Jaw length
E F
Knife length Point thickness C
D
Jaw width Jaw thickness
Fig. 13.10 Various types of pliers
Pliers have different shapes of handles, though the most common are those with curved handles.
They are designed for maximum comfort and efficiency. Extended handles are provided on some long nose and Duck Bill pliers for longer reach and increased leverage. While using pliers to cut a wire or metal piece, ensure the protection of eyes with goggles.
Soldering, Assembly and Re-working Techniques 475
A good pair of pliers is invaluable as a precision extension of your fingers when holding and forming components for PCBs. When bending resistor or axial capacitor leads to the correct pitch for your design, the pliers will give you a professional finish and avoid stress to the lead/component joint. Usually, a pair of ‘snipe nose’ pliers will suit most applications. The fine tip will enable you to use it like a strong pair of tweezers and the serrated jaws will give you a good grip when holding and forming different wires and parts.
The two mostly commonly types are non-serrated round nose pliers and long nose pliers. The pliers having serrated jaws, row of sharp points along the edge can damage the wire and its insulation if not properly used. Round nose pliers are useful for forming wires and component leads providing a smooth curve to any bends. However, one should take care not to squeeze them too hard, otherwise they may cause damage by making indentations in the wire.
Both pliers and cutters are easy to use when they are fitted with springs, which keep them open.
This allows one-handed operations.
a Round Nose Pliers: Round nose pliers are useful for forming wires and component leads.
With the help of this particular tool, one can provide a smooth curve to any bend. However, one has to take care not to squeeze them too hard otherwise they can damage the wires by making indentations on them.
a Long Nose Pliers: They are used for accurate assembly work in hard-to-reach areas.
13.7.3 Strippers
Strippers are used to remove insulation from the wires. The most usually employed stripers are of the cutting type (Figure 13.11). These strippers are so designed that they can accommodate various sizes of wire normally used in electronic equipment. To prevent damage to the wire by nicking, it should be ensured that the specific wire size hole is selected in the cutting stripper.
In the thermal strippers, the wire to be stripped is placed between two electrodes. The electrodes get heated when elec-
tric current is passed through them. The resulting heat melts the insulation. When using thermal strippers, toxic fumes emanating from compounds such as polyvinyl chloride or polytetrafluoroethy- lene must be properly exhausted by using some type of fan ventilation system.
Hot-blade, rotary, and bench wire strippers are generally used in shops where large wire bundles are made. When using any of these automatic wire strippers, the manufacturer’s instructions should be followed for adjusting the machine; to avoid nicking, cutting, or otherwise damaging the conductors.
The following procedure is adopted for stripping wire with the hand wire stripper:
a Insert the wire into the centre of the correct cutting slot for the wire size to be stripped. The wire sizes are generally listed on the cutting jaws of the hand wire strippers beneath each
Fig. 13.11 Wire stripper
slot. After inserting the wire into the proper slot, close the handles together as far as they will go.
a Slowly release the pressure on the handles so as not to allow the cutting blades to make contact with the stripped conductor. On some of the hand wire strippers, the cutting jaws have a safety lock that helps prevent this from happening.
a Continue to release pressure until the gripper jaws release the stripped wire, and then remove it completely.
Be careful not to nick a wire. Even if the wire doesn’t break, a cut reduces its diameter and thus its capacity to conduct electricity. This is dangerous and could lead to an electrical failure.
13.7.4 Bending Tools
Bending tools are pliers having smooth bending surfaces so that they do not cause any damage to the component.
13.7.5 Heat Sinks
Some components such as semiconductor devices, meter movements and insulating materials are highly heat-sensitive. They must be protected from damage due to heat while soldering. Devices such as a set of alligator clips, nose pliers (Figure 13.12) commercial clip-on heat sinks, felt-tipped tweezers, and anti- wicking tweezers and similar such devices are usually placed or clamped at the site of soldering so that they prevent the heat from reaching the components.
13.7.6 General Cleaning Tools
Before the soldering process is actually performed, the surface on the printed circuit board or the compo- nent leads must be properly cleaned. The tools or devices most commonly used for general cleaning are alcohol dispenser, camel hair brush, small wire brush, synthetic bristle brush, cleaning tissue, pencil erasers, (Figure 13.13) typewriter erasers, braided shielded tool, and sponge with holder, tweezers and single-cut file.
A very useful soldering aid consists of a plastic or wood wand with a pointed metal tip at one end and a
Pencil soldering iron Needle nose
pliers as heat sink
Wipe toward the edge of the card Fig. 13.12 Use of pliers as heat sink in soldering
Fig. 13.13 Use of pencil eraser as a cleaning tool
Soldering, Assembly and Re-working Techniques 477
notched metal tip at the other. The blunt end of the aid is used to clear solder from holes in printed circuit boards and from solder lugs. The notched end can be used to make right-angle bends in component leads, to hold leads and wires while the solder joint is made, and to keep leads away from pc boards and lugs during desoldering operations.