The PWB assembly industry is undergoing
monumental changes in PWB soldering materials brought on in large part by restrictions in CFC use as
a cleaning media. Additionally, PWB designs calling for SMD's, finer pitch and smaller lines and spaces
have resulted in dramatic changes in solder mask, component and soldering technologies. Compounding
these technical challenges are severe competitive issues which necessitate an increasingly cost-effective
PWB assembly operation. Reduction of soldering defects is a key goal in lowering cost per assembled
module.
The following table will assist PWB fabricators,
assemblers, and related personnel in analyzing wave solder defect situations and exploring plausible
solutions. Reasonable starting points for a typical wave soldering process would include a solder pot
temperature of 475 °F, a top side pre-heat which reaches 200° F, and a line speed of 4-6 fpm.
The PWB should not vertically penetrate the solder wave more then 1/3 of its thickness. Optimization
of the wave solder process may require deviations from the above norms.
| Condition |
Possible Cause |
Corrective Action
|
| Pinholes/ blowholes/
solder voids |
Gas evolution |
Prebake PWB to remove moisture
|
| Improper flux specific gravity
|
Adjust to manufacturers
recommendation |
| Conveyor speed too high
|
Reduce conveyor speed |
| Preheat temperature too
low |
Increase preheat temperature
|
| Solder temperature too low
|
Increase solder temperature
|
| Solder
spattering/ solder balls |
Gas evolution |
Prebake
PWB to remove moisture |
| High flux
specific gravity |
Adjust/lower
specific gravity |
| Erratic
solder wave |
Adjust/level
wave |
| Preheat
temperature too low |
Increase
preheat temperature |
| Solder
temperature too low |
Increase
solder temperature |
| Conveyor
speed |
Alter
conveyor speed |
| Solder
mask film properties |
Contact
PWB or Solder Mask vendor |
| Dewetting/Poor
Wetting |
PWB or component solderability
|
Check solderability per
IPC-S-804B |
| Improper preheat temperature
|
Increase preheat temperature
|
| Improper solder temperature
|
Increase solder temperature
|
| Improper conveyor
speed |
Reduce conveyor
speed |
| Bridging/Webbing/
Shorting |
Improper
lead clinching |
Change
clinch angle and/ or length |
| Improper
fluxing |
Adjust
fluxer so as to ensure a uniform film on the entire PWB |
| Erratic
solder wave |
Adjust
level; clear nozzles and screen |
| Solder
contamination |
Replace
solder |
| Low solder
temperature |
Increase
solder temperature |
| Conveyor
speed |
Adjust
by experimentation |
| Solder
mask film properties |
Contact
PWB or solder mask |
| Icicles/Spikes |
Improper flux system |
Use flux with higher specific
gravity |
| Improper wave shape and/
or angle |
Adjust wave and/or angle
|
| Improper conveyor speed
|
Decrease conveyor speed
|
| Low solder temperature |
Increase solder temperature
|
| PWB or component
solderability |
Check solderability
per IPC-S-804B |
| Non-shiny
solder fillets/joints |
Solder
contamination |
Replace
solder |
| Conveyor
speed, pre-heat and solder temperature
|
Adjust
preheat, solder temperature and
conveyor speed to establish proper relationship |
| Mechanical
disturbance prior to solder solidification |
Check
wave solder conveyor system for abnormalities |
| Excess solder-PWB
solder side |
Chip component
orientation |
Redesign land
area so that both chip terminations
see equivalent solder cycle |
| Improper conveyor speed
|
Reduce conveyor speed |
| Improper time-temperature
relationship |
Adjust preheat,
solder temperature and conveyor
speed to establish proper relationship
|
| Improper wave/conveyor angle
|
Adjust to 5 ° - 7 °
|
| Excess
solder-PWB component side |
Solder
wave too high |
Lower
conveyor or adjust wave height |
| Conveyor
too low |
Raise
conveyor |
| Inadequate
pallets/fixtures |
Rework
or redesign pallets/fixture |
| PWB
warpage |
Fixture
PWB; Inspect incoming PWBs for
maximum warpage |
| Holes
or cut-outs in PWB |
Review
design |
| Insufficient
PTH fill |
Contaminated
componentlead or PTH |
Check cleanliness
andsolderability |
| PTH/Component lead ratio
|
Increase PTH diameter |
| Low preheat temperature
|
Increase preheat temperature
|
| Low flux specific gravity
|
Increase flux specific gravity
|
| Low solder temperature |
Increase solder temperature
|
| Improper conveyor speed
|
Reduce conveyor speed |
| Large heat sink |
Increase top-side preheat
|
| Solder contamination |
Replace solder |
| Insufficient
Solder- PWB Solder side |
High solder
temperature |
Reduce
solder temperature |
| Improper
conveyor speed |
Increase
conveyor speed |
| Excess
drainage on long leads |
Reduce
lead length |