Printed circuit board (PCB) welding defect analysis

Correct solder joint design and good process (ie, circuit board welding process), is a key factor for reliable welding. So-called "reliable" the solder has all of the requirements of nature, not only in the product produced in the entire service life of the electronic products should be guaranteed to work correctly.

The welding is actually a chemical process. The printed circuit board (PCB) is a support member of the circuit components and devices in the electronic products, which provides the electrical connection between the circuit components and devices. With the rapid development of electronic technology, increasing the density of the PCB, more and more layered, and sometimes may all designs are correct (such as the circuit board there is no damage to the printed circuit design perfect, etc.), but due to problems in the welding process, welding defects, welding quality and thus affect the pass rate of the circuit board, which led to the quality of the machine is unreliable. Therefore, the factors affect the quality of welding of the printed circuit board must be analyzed, analyzing the causes of welding defects to be improved to make the entire circuit board soldering quality is improved, and for these reasons.

, Resulting in welding defects reasons

PCB design affect the quality of welding

In the layout, the the PCB size too large, although welding is easier to control, but the printing lines long, impedance increases, the decreased ability of the anti-noise, cost increase; excessively small, the heat decreased, welding is difficult to control, prone to the adjacent lines. interference, such as circuit boards electromagnetic interference. Therefore, it is necessary to optimize the design of the PCB board: (1) shorten the connection between the high-frequency components, reducing EMI interference. (2) The weight of a large (such as more than 20g) components should the bracket, and then welded. (3) heating elements heat issues should be considered to prevent larger ΔT component surface defects and rework, thermal components should be kept away from heat sources. (4) the arrangement of the components as much as possible in parallel, this is not only beautiful but also easy to weld, should be high-volume production. The circuit board is designed to 4 warpage generated weld defects

PCB and components warping occurs in the welding process, the Weld, short circuit and other defects due to stress deformation generated. The warpage is often due to the imbalance of the temperature of the upper and lower portions of the PCB. On a large PCB, the plate itself weight fall will produce warpage. Ordinary PBGA device from the printed circuit board is about 0.5mm, circuit board devices, along with the return to normal shape after cooling circuit board solder joint will for a long time is under stress, if the devices raise 0.1mm enough to cause open Weld.

Warped simultaneously on the PCB, the components themselves may warp, solder joints at the center of the element is lifted away from the PCB, to produce the air welding. This often happens when only using the flux and solder paste fill gaps. When using solder paste, since the deformed leaving the solder paste and solder balls are connected together to form a short-circuit defect. Another reason is shorted Delamination occurred in the element substrate in the reflow process, the characteristics of defects below the device is due to internal expansion forming a bubble, can be seen in the X-ray detector to a short circuit welding is often the middle of the device .

In summary, improved by optimizing PCB design, excellent solder circuit board holes weldability and prevent warping prevent the generation of defects that can improve the quality of the entire circuit board soldering.