3.2. Steps of Work

In practice, there is a variety of forms of soldered joints. The preparation for soldering, however, is always the same.

The following steps are involved:

· Cutting to length and stripping of conductors

The stripping length depends on the relevant use. Stripped conductors must not be notched - risk of breakage!

Tools for stripping of conductors:

· Cleaning of soldering surfaces

Soldering surfaces are stripped conductors, leads (pigtails) of components as well as connections of conductors and components. For making a proper soldered joint it is necessary to clean the surface to be joined by soldering. Denpending on the soldering surface, cleaning is done by

· Flux-treatment of soldering surfaces

Why must soldering surfaces be treated with flux prior to soldering?
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· Tin-coating of soldering surfaces

With thin-coating a material-closed joint is made by heating the soldering surface above the melting point temperature of the solder by means of a soldering device and by supplying solder on the soldering surface.

· Making soldered joints

Soldered joints are material-closed joints (bonds) of two solderable metals. There are different forms of soldered joints:

- Wire-to-wire joints as parallel, cross or hook joints as well as soldered joints with twisted wires. Parallel and cross joints are mechanically connected by the solder only and, therefore, can be more easely detached. Hook joints and joints with twisted wires are mechanically stronger and more difficult to detach. The tin-coated wires are put together according to the type of joint. The joint is heated above melting-point temperature of the solder by means of the soldering iron and bonded with soldering tin added. Then the soldered joint must cool down with no displacement of the wires.

Figure 7 Soldering joints - 1 conductor, 2 soldering joint

7.1. single or parallel joints

7.2. cross joint

7.3. hook joint

7.4. twisted joint

- Wire and cable eye

The cable eye is to be selected depending on the size of the conductor and to be tin-coated, if necessary. A flexible insulating tube is to be slipped over the conductor and, after soldering, over the cable eye and to be fed into the cable eye. The joint is to be heated by means of a soldering device and when adding solder the sleeve of the cable eye is filled. It is to be made sure that the wire end and cable eye form a clear end.

Figure 8 - Wire and cable eye - 1 point to be soldered is to be tin-coated

- Wire and soldering tags

Figure

Soldering tags are produced in various forms. The wire is to be led into the respective tag and to be clamped in place by a flat nose plier. Then the soldering tag is heated by means of the soldering iron and by adding soldering tin the joint is made.

Figure 9 - Wire and soldering tags - 1 correct, 2 incorrect

- Component and soldering tag

What steps are required for joining a component and soldering tag?
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- Component and wire

A component-wire-joint is made like a hook type soldered joint.

Figure 10 - Component and wire

- Components on printed circuit boards

Soldering on printed circuit boards is to be done quickly and exactly. The soldering iron's capacity should not exceed 60 W so as not to destroy the sensitive semiconductor components by high temperature. The leads of the components are to be bent and cut to length according to the hole spacing on the printed circuit board and to be tin-coated, if required. The component is to be inserted and the soldering eye and the lead are to be heated from the conductor end by means of a soldering iron adding solder.

Figure 11 - Components and printed circuit boards - 1 lead, 2 soldering point, 3 printed circuit board trace

Figure 12 - Replacing a component - 1 separation point of the defect component, 2 soldering point of the new component, 3 component

What steps are required for replacing a component in Figure 12?
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· Inspection of the soldered joint

A correct soldered joint features:

- a consistent, bright surface,
- perfect bond between the solder and the parts connected,
- no holes or inclusions in the surface,
- a mechanically strong connection.

What are the causes for a bad soldered joint showing the following faults?