一．Common defect phenomenon in wave soldering
Wave soldering process is the main process of PCBA component defects, in the whole PCBA assembly process it causes defects up to 50%. Wave soldering defects in the process is a concentrated manifestation of the problems in the manufacturing of the previous process. These defects can be distinguished as obvious and hidden two categories. The former are easier to detect and the main problem is the latter. This chapter focuses on the defective phenomena common to both leaded and lead-free wave soldering.
These common defects are mainly manifested as false soldering, cold soldering, not wetting, anti-wetting, solder joints contour shape (hereinafter referred to as the shape of the laying) poor, bridging, pulling the tip of the hole, through the hole, hole, pinhole, "cannon" hole, disturbed solder joints or broken solder joints, dark solder joints or granular solder joints, and so on.
二．Void soldering
Definition
The surface of the welded joint is rough granular, poor gloss, poor mobility is the appearance of the appearance of false soldering. Essentially, where in the welding process in the connection joint interface does not form a suitable thickness of the alloy layer (IMC) can be judged as a virtual welding, as shown in the figure below. At this point, if the solder joint is torn, it can be found in the base metal and brazing material between the base metal and the brazing material without any wedge each other's residue, the interface is flat and clear, as if the paste with the paste to stick the same. The normal solder joint is torn, brazing material and base metal between each other into a crisscross of cracks, that is, the base metal on the brazing material residue, brazing material also has traces of the base metal. 
Phenomenon
False soldering connection interface neither wetting nor diffusion, as if stuck with paste, the surface of the solder joint is rough shape, poor gloss, contact angle θ> 90 °, as shown in the figure below. At this time, the brazing material and the base metal joint interface for a layer of non-weldable film blocked, the interface layer failed to occur on the expected metallurgical reaction, this is a kind of visible virtual welding phenomenon, from the appearance can be judged.
三．Cold Welding
Definition
In the wave soldering joint interface, although the wetting occurred but did not occur the required diffusion process, joint interface alloy layer (IMC) formation is not obvious, can be defined as cold welding, as shown in the figure below.
Phenomenon
The surface of the cold solder joint appears to be wet, but the brazing material and the base metal bonding interface does not occur metallurgical reaction, not the formation of the appropriate thickness of the alloy layer (IMC), as shown in the figure below. It indicates that there is no problem with the solderability of the PCB and components, and the root cause of this phenomenon is the improper selection of process conditions for soldering. It is an invisible defect phenomenon, the appearance is not easy to determine, and therefore extremely harmful.
三．Prevention of defective phenomena
Strictly control the outsourcing, outsourcing parts warehousing acceptance must be poor solderability PCB and components rejected, so we must strictly implement the warehousing acceptance procedures
① After the arrival of each batch of purchased components, must be sampled according to IPC/J-STD-002 standard requirements for weldability test, qualified before the formal warehousing.
② Each batch of outsourcing PCB should be arbitrarily sampled after the arrival of 3 pieces of IPC / J-STD-003 standard requirements for solderability test, qualified before acceptance. Because the PCB after the solderability test can not be reused, so each batch of orders must be added to the 3 pieces of process test pieces.
Strengthen the civilized hygiene management in process transfer
① Staff should wear anti-static clothing, shoes and gloves, and keep them clean.
② Most fluxes can only remove rust and oxide film, but not organic film like grease. If components and PCB in the storage and production transfer process, stained with grease and other contaminants, it will produce tin, lead polarization and pinholes, reducing solder strength. It is also easy to produce cracks in the lead segregation bit and brazing material connection interface, which is not abnormal from the outside, but lurks as a factor affecting reliability. Since hand sweat stains, etc., are the cause of poor solderability during the transfer process, anything that comes into contact with the soldering surface during operation must be clean. hands should wear gloves that comply with EOS/ESD protection requirements when and after the PCB is removed from the storage bag and should only touch the corners or edges of the board of the PCB.
