Principle of soldering and action of suitable flux
- Mating surfaces are degreased and pickled before soldering.
- Components are assembled or jigged as necessary.
- Surfaces to be soldered are coated with flux to dissolve any remaining oxide films, and to promote wettability.
- Copper soldering bit heats the solder and conveys solder to the workpiece. In mass production, various forms of heating are used, including "vapour-phase" soldering.
Manufacture:
- Surface preparation – degreasing using organic solvents and/or alkaline solutions. Abrasive cleaning and pickling to remove oxide films.
- Assembly/jigging (see Brazing L01) – where possible joints should be self-locating.
- Heating – mass soldering uses the molten solder as a heat source to melt the pre-coated flux. Direct coating uses a separate heat-conducting source: soldering iron, hot plate or hot-oil immersion. Non-contact methods use ovens, gas burners and induction heating. Comparison of heating methods:
- Flame: low cost and output, highly versatile, hand-feed systems
- Electrical resistance: medium cost and output, poor versatility, preforms required
- Radio-frequency induction: high cost and output, preforms required
- Dipping bath: medium cost, low output and versatility
- Soldering iron: hand-feeding gives low cost and output, but high versatility
- Finishing – flux and residual solder are removed before inspection.
Materials:
- Metals that do not readily oxidise (Sn, Cu, mild steel, Ni Au and Ag) are most easily soldered.
- Solders usually contain tin to promote surface wetting. Special solders with melting points up to 365˚C are available.
| Grade | % Tin | % Lead | % Antimony | Melting range (˚C) | |
| A | 64 | 36 | - | 183 - 185 | |
| K | 60 | 40 | - | 183 - 188 | |
| F | 50 | 50 | - | 183 - 212 | |
| R | 45 | 55 | - | 183 - 224 | |
| G | 40 | 60 | - | 183 - 234 | |
| H | 35 | 65 | - | 183 - 244 | |
| J | 30 | 70 | - | 183 - 255 | |
| V | 20 | 80 | - | 183 - 276 | |
| W | 15 | 85 | - | 227 - 288 | |
| B | 50 | 47 | 3 | 185 - 204 | |
| M | 45 | 52.3 | 2.7 | 185 - 215 | |
| C | 40 | 57.6 | 2.4 | 185 - 227 | |
| L | 32 | 66.1 | 1.9 | 185 - 243 | |
| D | 30 | 68.2 | 1.8 | 185 - 248 | |
| N | 18 | 80.9 | 1.1 | 185 - 275 | |
| Uses | BS 219 grades | ||||
| Electrical |
General electrical soldering (by hand) Printed-circuit mass-soldering Electric-lamp bases Electric cable conductors Wiped joints on lead cable-sheath |
K, F A, K V, W H, J L, D |
|||
| General Engineering |
General sheet-metal work (steel, copper, tinplate) General sheet-metalwork (brass, galvanised sheet) |
K, F, R, G, B, M, C K, F |
|||
| Automotive |
Heat-exchangers, automotive radiators, refrigerators Auto-body patching and filling |
G, J C D |
|||
| Others |
Capillary plumbing joints Dip-soldering (non-electrical) Coating (pre-tinning) Food-can soldering |
K, F, G C, D, N K, G K, F, G |
|||
Design:
- Optimum gaps are 0.08–0.18 mm. Below 0.08 mm vapour may be trapped, over 0.18 mm no capillary action.
- Lap joints are essential.
- Additional mechanical strength is possible.
- Solder preforms (BS 1723) affect joint shape.
- Designs for soldering components onto printed circuit boards, depend on the strengths required.
See Also: Adhesive bonding, Brazing and Fasteners
This article is a part of Manupedia, a collection of information about some of the processes used to convert materials into useful objects.
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