16.Misalignment(IC 偏移 )

拒收 良好情r

缺c描述 :

Component not centered on pad and has shifted sideways or rotated.

ACCEPTABILITY

Defect is consider acceptable if the component do not misaligned by more than 50% off the pads

PROBABLE CAUSES

Improper design of component pad (wrong dimension)
Placement error
Differential heating between adjacent pads

Space orientation between pads
Component movement during handling
Wetting force and surface tension causing component to drift off

POSSIBLE PREVENTIONS

If the placement is by machine, check the placement of the PCB board in the machine or the program of the machine used for placement

Vibration should be minimised to avoid misplacement
Designing of the PCB must be accurate in the first place to avoid double work

REWORK

For multilead, fine-pitch component and IC :
A thermode( heated tool of a shape which conforms to the pattern of the footprints of IC ) is pressed downwards against the horizontal ends of the gullwing legs to melt all the solder joints before a tweezer is used to align the component back.

For SMD :
The solder joint is heated long enough with the help of a chisel-shaped soldering tip so that the transfer of heat is sufficient enough to melt the joint before a tweezer is used to align the component back.