Circuit board soldering defects caused by the three major elements Detailed
Soldering defects caused by the circuit board the following three factors:
1, solderability of the circuit board hole affect the quality of welding
Circuit board hole solderability is poor, will have Weld defects, affecting the circuit components of the parameters, resulting in multi-layer components and the inner layer of the conduction instability, causing the entire circuit failure. The so-called solderability is the nature of the molten metal wetting the surface of the solder, where the solder metal surface to form a relatively uniform continuous smooth film.
Factors that affect the solderability of the printed circuit board are: (1) the composition of the solder and the nature of the solder to be soldered. Solder is an important part of the chemical process of soldering. It consists of a chemical material containing flux. The common low melting point eutectic metal is Sn-Pb or Sn-Pb-Ag. The content of impurities should be controlled by a certain fraction , In case the oxide produced by the impurity is dissolved by the flux. The function of the flux is to help the solder wet the surface of the soldered circuit by transferring heat and removing rust. White rosin and isopropanol solvents are generally used.
(2) Soldering temperature and the degree of metal surface cleaning can also affect solderability. When the temperature is too high, the diffusion speed of the solder is accelerated. In this case, the high activity causes the surface of the circuit board and the solder to be rapidly oxidized, resulting in welding defects. Contamination of the circuit board surface also affects the solderability and causes defects. These defects Including tin beads, solder balls, open, poor gloss and so on.
2, warpage generated welding defects
Circuit boards and components in the welding process of warping, resulting in stress Weld, short circuit and other defects. Warpage is often caused by temperature imbalance in the upper and lower parts of the board. For large PCBs, warping occurs due to the weight of the board itself. Ordinary PBGA devices are about 0.5 mm from the printed circuit board. If the device is large on the circuit board, the solder joint will be under stress for a long time as the circuit board resumes its normal shape after cooling, which is sufficient if the device is raised by 0.1 mm Weld open.
3, the design of circuit board affect the quality of welding
In the layout, the circuit board size is too large, although the welding easier to control, but printing long lines, the impedance increases, anti-noise ability decreased, the cost increases; too small, the heat decreases, the welding is not easy to control, prone to adjacent lines Mutual interference, such as circuit board electromagnetic interference and so on. Therefore, you must optimize the PCB design:
(1) shorten the connection between high-frequency components to reduce EMI interference.
(2) heavy components (such as more than 20g) components, should be fixed bracket, and then welded.
(3) heating element should consider the issue of heat to prevent the surface of a larger ΔT defects and rework, thermal elements should be far away from the heat source.
(4) the arrangement of components as parallel as possible, so that not only beautiful and easy to weld, should be mass-produced. The circuit board is best for a 4: 3 rectangle. Do not change the width of the wire to avoid the wiring discontinuity. When the circuit board is heated for a long time, the copper foil tends to swell and fall off. Therefore, the use of large area copper foil should be avoided.