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Circuit board soldering technology in recent years, the electronics industry process development history, can be noted that a very obvious trend is the reflow soldering technology. In principle, conventional plug-in components can also be reflow soldered, which is commonly referred to as through-hole reflow soldering. The advantage is that it is possible to make all solder joints at the same time, thus minimising production costs. However, temperature-sensitive components limit the application of reflow soldering, both for inserts and SMDs. Attention has then turned to selective circuit board soldering. In most applications, selective board soldering can be used after reflow soldering. This will be an economical and efficient way to complete the soldering of leftover inserts and is fully compatible with future lead-free soldering.
Six ways to solder circuit board components. Please refer to the following:
1.Arc welding Welding circuit boards
Arc welding uses the heat of the melting arc of the workpiece to achieve the connection. Arc welding is a common welding method. There are two basic types. One is multiple arcs. Melting electrode is a non-melting electrode arc, in which the electrode does not melt, filler metal needs to be added to the liquid pool alone.
2.Plasma Welding Welding circuit boards
Welding Plasma arc welding belongs to scintillation welding, is a high concentration of plasma welding beam welding arc on the melted base metal welding method. Plasma welding speed, there are open bevelled, good welding performance, weld thermal effect. Area is small, welding deformation and residual stress is small, can weld a variety of metals.
3.High-frequency welding Welding circuit boards
High-frequency welding, including resistance welding and inductive hf welding. It uses the ‘skin effect’ 60-500khz high-frequency current to heat the surface of the metal being welded, so that it melts instantly, and then welded together under pressure. It is used to weld straight seams of pipelines (round pipe, square pipe, profiled pipe, profiled steel, etc.) with high production efficiency. Clean the metal surface before welding, basically no welding dust.
4.Gas welding Welding circuit boards
Gas welding is a use or gas flame to melt the workpiece and the connection of the welding method. This welding has a variety of methods, including welding and welding oxyacetylene hydroxide according to the type of flammable gas classification. Chemical reaction of the heat generated, usually using acetylene as a flammable gas
5.Argon arc welding Welding circuit boards
Argon arc welding blinking belongs to the welding, welding will produce strong ultraviolet rays. Divided into non-molten argon arc welding and molten argon arc welding argon arc welding. Argon arc welding can be carried out with a mobile hoover. At the same time, the welding station should ensure good ventilation to ensure the health of the welder.
6.Resistance welding Welding circuit boards
Resistance welding is the use of pressure on the electrodes, and retain the heat generated by the welding current, the actual joining class of welding methods, including spot welding, seam welding, convex welding, resistance welding and electrode welding. Resistance is usually used automatically in welding equipment, fitted with various electrical control systems and improved mechanical controls.
Circuit board welding defects
1. The weldability of the circuit board holes affects the welding quality.
Circuit board holes weldability is not good, will produce virtual welding defects, affecting the parameters of the components in the circuit, resulting in multi-layer board components and the inner layer of the wire conduction instability, resulting in the failure of the entire circuit function. The so-called solderability is the nature of the metal surface wetted by molten solder, that is, the solder on the metal surface of the formation of a relatively uniform layer of continuous smooth adhesion of the film. The main factors affecting the solderability of printed circuit boards are:
The composition of the solder and the nature of the solder. Solder is an important part of the welding chemical treatment process, which contains flux chemical data composition, commonly used low melting point eutectic metal for Sn-Pb or Sn-Pb-Ag. Which impurity content to have a certain sub ratio control, in order to prevent impurities generated by the oxide flux dissolved. The function of the flux is to transfer heat to remove corrosion to help solder to wet the surface of the circuit board being soldered. Generally, white rosin and isopropyl alcohol solvent are used.
Solderability is also affected by the soldering temperature and the cleanliness of the metal plate surface. Temperature is too high, then the solder diffusion speed accelerated, this time with high activity, will make the circuit board and solder fusion surface rapid oxidation, resulting in soldering defects, circuit board surface contamination will also affect the solderability to produce defects, these defects, including tin beads, tin balls, open circuit, bad gloss.
2. Soldering defects caused by board warpage
Circuit boards and components in the welding process to produce warpage, due to stress deformation and produce virtual welding, short circuit and other defects. Warpage is often caused by the temperature imbalance between the upper and lower parts of the circuit board. For large PCBs, warpage can also occur due to the weight of the board itself falling. Ordinary PBGA device from the printed circuit board about 0.5mm, if the circuit board device is larger, with the circuit board after cooling back to normal shape, the solder joints will be under stress for a long time, if the device is raised 0.1mm will be enough to lead to open circuit soldering.
3. The design of the circuit board affects the quality of soldering
In the layout, circuit board size is too large, although welding is easier to control, but the printed line is long, impedance increases, anti-noise ability to decline, the cost of new; too small, then the heat dissipation is reduced, the welding is not easy to control, easy to neighbouring wires interfering with each other, such as circuit boards, electromagnetic interference and so on.
Collectibles, must optimise the PCB board design
Shorten the connection between high-frequency components, reduce EMI interference.
Heavy components (e.g. over 20g) should be fixed with brackets and then soldered.
Heat generating components should be considered for heat dissipation to prevent defects and rework due to large Δ T on the surface of the components, and heat sensitive components should be kept away from heat sources.
The components should be arranged as parallel as possible, which is not only aesthetically pleasing but also easy to solder to the circuit board, and is suitable for mass production.