1. The weldability of circuit board holes affects welding quality
It is difficult to weld the circuit board hole, it will produce false welding defects and affect the parameters of the components in the circuit, resulting in the instability of the multi-laminated components and the inner layer conductance, resulting in the failure of the whole circuit function.The solderability is the property of the metal surface being wetted by the melt solder, that is, the metal surface of the solder is formed by a relatively uniform continuous smooth adhesive film.The factors affecting the solderability of printed circuit boards include:
(1) the composition of solder and the properties of solder.Solder is an important part of the welding in the process of chemical treatment, it is composed of containing flux of chemical materials, commonly used low melting eutectic melting metal for Sn – Pb/Sn Pb – Ag of impurity content to a certain ratio control, to prevent dissolve impurities generated oxide by flux.The function of the flux is to help the solder moisten the surface of the welded plate by passing the heat and removing the rust.White rosin and isopropyl alcohol are commonly used.
(2) welding temperature and surface cleanliness of metal plates may also affect solderability.Temperature is too high, the solder diffusion speed, has the very high activity at this time, can make the circuit board and solder melt oxidation surface rapidly, produce welding defects, circuit board surface pollution can also affect the weldability to produce defects, these defects including tin beads, tin ball, open circuit, glossiness is bad, etc. 
2. Welding defects caused by warping
The circuit boards and components produce warping during welding process, and the defects such as virtual welding and short circuit are produced due to stress distortion.Warping is often caused by the uneven temperature of the upper and lower part of the circuit board.For large PCB, the weight of the plate will also warp.Ordinary PBGA device about 0.5 mm from printed circuit boards, if larger components on printed circuit boards, temperature returned to normal after the shape as the PCB, solder joint will be under stress for a long time, if the device is 0.1 mm is sufficient to cause the virtual welding
3. The design of circuit boards affects welding quality
In the layout, when the circuit boards are too large, while the welding is easier to control, the printing line is long, the impedance increases, the anti-noise ability decreases, and the cost increases.After an hour, the heat dissipation decreases, the welding is not easy to control, easy to appear adjacent lines interference, such as the electromagnetic interference of the circuit board.Therefore, the PCB board design must be optimized:
(1) to shorten the connection between the high frequency components and reduce EMI interference.
(2) the weight (eg, more than 20 g) should be fixed with a bracket and then welded.
(3) heating elements should be considered heat dissipation problems, prevent components surface has larger Δ T defects and rework, thermal element should be far away from heat source.
(4) the arrangement of elements is as parallel as possible, so that it is not only beautiful but also easy to weld, which is suitable for mass production.The circuit board is designed for 4:3 rectangular best.The conductor width should not be changed to avoid the discontinuity of the wiring.When the circuit board is heated for a long time, the copper foil tends to expand and fall off. Therefore, large area copper foil should be avoided.