Following are several soldering issues that may occur during solder training or production operations.
Cause: Inadequate removal/cleaning of flux residue after reflow.
Correction: RMA flux residues must be removed from the
assembly. On some assemblies or locations, no-clean fluxes
must also be removed.
Cause: Excess solder was applied to the connection during hand soldering.
Correction: Remove excess solder using fluxed
solder wick and soldering iron or a solder sucker.
Cause: Insufficient heating of the solder connection.
Correction: Flux the connection on both sides of
the PCB. Contact both the pin and pad with a soldering iron and reflow. Add solder as necessary.
Cause: Surface contamination on the soldered surface.
Correction: Clean both sides of the PCB with PCB cleaner and brush. Flux both sides and reflow from the bottom side. Add solder as required.
Cause: During solder solidification, solder may separate at the grain boundary as it contracts. More common in lead-free solders.
Correction: IPC-610G states there is no defect associated with this anomaly provided the connection meets all other acceptance criteria.
Cause: Poor solder wetting on the component or insufficient solder volume.
Correction: Clean the component and both ends with
PCB cleaner and brush. For resistors, flux and reflow
each end. Add solder as necessary. For chip caps, use
hot air reflow.
Cause: Excessive solder, or excessive pad size vs. pad gap.
Correction: Clean both sides of the PCB with PCB cleaner and brush.
Flux both sides. Use solder wick and soldering iron or solder sucker to
remove excess solder from the bottom side. Clean both sides.
Cause: Insufficient solder application during hand soldering.
Correction: IPC J-STD-001G specifies minimum solder fillet height on 1, 2, 3
and 5-sided SMT chip components for Class 1, 2, and 3 applications.
Cause: Incorrect side placement of the chip component on its mounting
Correction: IPC-610G specifies Maximum Side Overhang of
50%(W) for Classes 1 and 2 and 25%(W) for Class 3 chip
Cause: Insufficient heat applied to lead during hand soldering reflow.
Cause: Application of excess solder during hand soldering.
Correction: Flux the connection and use a soldering iron to
draw off the excess solder. Or, remove the excess solder
using solder wick and soldering iron.
Cause: “Operator error” in installing the component onto the PCB.
Cause: Incomplete reflow (melting) of solder paste balls during the reflow cycle.
Correction: Flux the lead, pad, and topside. Reflow lead
and pad by concurrent contact with the soldering iron.
Cause: Poor circumferential wetting of the pad. Poor wetting of the lead barrel.
Cause: Imbalance of solder joint surface tension in molten solder causes the “stronger” joint (right side) to lift the component up off the board, creating the “tombstone.”
Correction: Correct this defect by fluxing and reflowing the chip
component using hot air or thermal tweezers (not on chip caps).
Or, alternate reflow of chip terminations via soldering iron.
Cause: Misplacement of the chip component end placement on its mounting pads.
Correction: J-001G requires “Minimum End Overlap” for Classes
1 and 2, and 25% R for Class 3 where R = Termination Length.