ULiROBOTS: Solve PCBA soldering defects using automatic soldering machines

ULIrobots：Use automatic soldering machine to solve PCBA welding defects. First, analyze what factors affect the welding of circuit board:

1, The solderability of the circuit board pad affects the welding quality

The poor solderability of the circuit board solder pad will lead to defects of false soldering, which will affect the performance of the components in the circuit, lead to the instability of the multilayer board components and inner layer lines, and cause the failure of the whole circuit function. So-called solderability is the property of the metal surface is wetting by molten solder, that is, the metal surface where the solder forms a layer of relatively uniform continuous smooth adhesion film. The main factors affecting the solderability of printed circuit boards are:
(1) the composition of the solder and the nature of the solder. Solder is an important part of the welding chemical treatment process, it is composed of chemical materials containing flux, commonly used low melting point eutectic metal for Sn-Pb or Sn-Pb-Ag where the content of impurities should have a certain percentage control, in order to prevent the oxide produced by impurities from being dissolved by flux. The function of the flux is to help the solder wet the surface of the soldered circuit board by transferring heat and removing corrosion. White rosin and isopropanol solvents are generally used. The use of automatic soldering machine, can be configured with different welding wire.
(2) Welding temperature and circuit board surface cleanliness will also affect the solderability. The temperature is too high, the solder diffusion speed is accelerated, this time has a very high activity, will make the solder pad and solder melt surface rapid oxidation, welding defects, welding pad surface pollution will also affect the solderability to produce defects, these defects include tin beads, tin balls, open circuit, poor brightness, etc.. The temperature of the automatic soldering machine is completely adjustable, which is a good solution to this problem.

Not all metals are suitable for soldering with tin. ULiROBOTS, after years of practice, have come to the following conclusions：

2. Welding defects caused by warpage of circuit board

The warpage occurs in the welding process of circuit board and components, resulting in defects such as soldering and short circuit due to stress and deformation. Warping is often caused by a temperature imbalance between the upper and lower parts of a circuit board .For large PCBs, warping can occur due to the weight of the board itself. An ordinary PBGA device is about 0.5mm away from the printed circuit board. If the device on the circuit board is large, the solder joint will be under stress for a long time as the circuit board recovers its normal shape after cooling. If the device is raised by 0.1mm, it will be enough to lead to open soldering. Solve the distance between the iron head and the solder joint is also a big advantage of the automatic soldering machine, through the handheld programmer to operate the Z axis, arbitrary adjustment of the iron head height. Configuration of four axis soldering machine can also be arbitrary rotation of the iron head, welding.

3, The design of the circuit board affects the welding quality

In the layout, the size of the circuit board is too large, although the welding is easier to control, but the printing line is long, the impedance increases, the anti-noise ability decreases, the cost increases; When it is too small, the heat dissipation is reduced, the welding is not easy to control, and the adjacent lines are easy to interfere with each other, such as the electromagnetic interference of the circuit board. Therefore, PCB board design must be optimized:
(1) Shorten the connection between high frequency components and reduce EMI interference.
(2) The components with large weight (such as more than 20g) 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 components as parallel as possible, which is not only beautiful and easy to weld, suitable for mass production. Circuit board design for the best 4∶3 rectangle. Do not change wire width to avoid discontinuity in wiring. When the circuit board is heated for a long time, the copper foil is easy to expand and fall off. Therefore, the use of large copper foil should be avoided.