7.Solder Ball( a球 )

拒收 良好情r

缺c描述 :

Solder balls adhere to PCB. Solder balls which appear around the pad or at the side of chips. This causes short circuit and low insulation to the joint.

PROBABLE CAUSES

Solder temperature too high
Solder wave height too low
Solder wave is uneven
Preheat temperature too low
Flux is contaminated
Flux specific gravity too low
No flux blow-off
Conveyor speed too high
Slumping of solder paste during pre-heating
Excessive paste

Defective fixture and pallet design
Board contamination due to insufficient board cleaning
Epoxy glass exposure
Defective mask material and excessive mask (temperature)
Moisture in laminate
Rough plated through hole
Paste is push out of place during insertion

POSSIBLE PREVENTIONS

Ensure that the solder pot temperature is set accordingly to the standard specification stated
Solder wave height should not be too high and should be flowing evenly as PCB travels across.
PCB must be preheated to the required temperature to avoid sudden temperature ramp.
Check for flux contamination and the specific gravity must stay within manufacturer’s specification
Ensure that there is no flux blow-off
Adjust the insertion pressure

Conveyor speed must be adjusted to a optimum rate
Ensure elimination of defective fixture
PCB must be free of contaminants
During fabrication, there should not be any hole
or pad misregistration and rough plated hole
Moisture should be eliminated in laminate
Mask material should be in good condition
Epoxy glass material must not be exposed
Make the solder deposit smaller

REWORK

Solder balls can be removed by touching it with the well-tinned tip of soldering iron.