[ Date Time : 2015-10-19 ] [ Comments : 0
Causes: 1: printing bad PCB is not clean (caused by oxidation of tin residues in PCB-PAD- again leading to a printing when mixed with the new paste, resulting the emergence of the phenomenon of false welding).
2: after solder paste kaifeng use no seal (solder paste is made up of solder powder and flux of the flux rosin water, are the important ingredients of solder paste if long time exposure interesting would be rosin. Leading to false welding)
3: steel mesh at both ends of the paste hardening (full automatic printing machine when the machine scraper will with solder paste, machine back printing will appear when the solder paste spillover phenomenon. The operator should every 10 minutes on both ends of the machine paste for cleaning. You can join in printing paste if time is short. If the time is too long, you need to stir or direct scrap disposal.
4: printed PCB after stored for a long time (lead solder paste drying. Principle and the same as the second〕
5: without warning jump (UPS power burning and electric power supply leads to unstable PCBA residence time in the furnace is too long)
6: extractor is polluted parts (components and solder from impurity substances caused by false welding)
7: excessive solvent (when cleaning the stencil into excess alcohol or alcohol wet production began to throw people make solder paste and mixed alcohol)
8: solder paste expired (solder paste after expiration of the solder paste flux will lose weight. Solder paste storage time should be no more than 6 months, had better be used up within 3 months)
9: reflow soldering temperature setting error