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.
- 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.
- 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|
General electrical soldering (by hand)
Electric cable conductors
Wiped joints on lead cable-sheath
General sheet-metal work (steel, copper, tinplate)
General sheet-metalwork (brass, galvanised sheet)
K, F, R, G, B, M, C
Heat-exchangers, automotive radiators, refrigerators
Auto-body patching and filling
G, J C
Capillary plumbing joints
K, F, G
C, D, N
K, F, G
- 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.
This article is a part of Manupedia, a collection of information about some of the processes used to convert materials into useful objects.