2-6 Cause Analysis of Some Undesirable Results

2-6-1 Solder ball

Ⅰ　Reflow doesn't happen for too long time after printing. 
   
 Ⅱ Print layer is too thick, causing tin overflow when components are pressed down.
 
 Ⅲ Paste boiling happens resulted from excessive temperature in the temperature riseing zone when reflow soldering is in operation.
 
 Ⅳ Over pressure when chip paste to cause the solder paste onto the printing ink.

2-6-2 Bridge:

Ⅰ　mainly occurs between the IC pins. 
   
 Ⅱ　solder paste overflow resulted from the thick screen 
 
 Ⅲ　The IC component is misplaced. Generally, the dislocation is no more than 1/3 of the pin width.
 
 Ⅳ　In the reflow profile, the setting time over the melt point is too long.
 
 Ⅴ　the pressure of the blade is too high and the pattern is blurry.

2-6-3 tombstone:

Ⅰ　Irregular printing. 
   
 Ⅱ　Tension is unbalanced on the two ends of the IC chip which will cause the chip erecting when the solder paste is melting. 
 
 Ⅲ　The preheating is not enough or the temperature field is irregular.

2-6-4 lack of solder：

Temperature is uneven on the screen, often high in the upper body and low in lower body, thus causing the solder to melt from the bottom. It could be solved by adjust the temperature field on the screen.

2-6-5 too much residue:

The setting of the temperature is unsuitable will cause this problem.

2-6-6 weak soldering

The soldering temperature is too low or the thermal capacity of some components on the PCB is too high. To prolong the soldering time or improve the peak temperature.