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Wave Soldering Defects - Inconsistent
or Poor Hole File
The solder has not fully filled the plated
through hole in Figure 1. This is due either to the pre-heat
being set too low or poor flux application. In both cases, a check
on the process parameters should eliminate the problem.
This is
a common problem seen when a company changes over from a foam
fluxer to a spray flux unit; it is due to the poor penetration
of flux
into the through hole.  |
| Figure 1: Solder has not fully filled the plated through
hole here. |
Poor or incomplete hole fill is normally a fluxing or heating
issue. It is uncommon for it to be a printed board problem. In Figure
2, the poor hole fill is due to pre heat settings. The solder has
wetted the
leads of the device but failed to wet the surface of the through hole.
As a guide, the topside temperature of the printed board just
before wave contact
should be 100-110°C. This is generally true for double sided and
multilayer boards. Single-sided boards will be processed at slightly
lower temperatures
as no solder penetration is needed.
 |
| Figure 2: The solder has failed to wet the surface of
the through-hole here. |
The solder has not fully filled the plated through hole in
Figure 3. This is either due to the pre heat operation being set
too low or poor flux application. In both cases a check on the process
parameters should eliminate the problem.
 |
| Figure 3: The solder has not fully filled the plated
through hole on the left. |
In Figure 4, one hole has filled and the second
has not, which should indicate the problem is less likely to be a printed
board
problem. Close examination shows that the solder has solidified on
one hole due to
the thermal demand of the component. By raising the pre heat or by
increasing wave contact time this problem should be simply overcome.
 |
| Figure 4: One hole has filled; the other has not. |
Poor hole fill can be caused by incorrect pre heat, no flux
or a total miss of the solder wave. In Figure 5 there is no evidence
of solder in the through hoes or vias. It is more than likely that
the board failed to make contact with the wave which could be due to
wave height, damaged
fingers or pallets not being maintained. Incorrect loading of the board
in to the systems may also have caused this fault.
It is possible that
the quality
of the through hole plating may have been responsible, but this
is less likely to be the case as it would be very apparent on other
boards in the batch.
 |
| Figure 5: It is likely that this board failed to make
contact with the wave. |
The example of poor hole fill in Figure 6 is fairly
unique as the problem is due to the legend on the printed board. Close
examination shows that poor design rules have allowed the legend to
contaminate the top of the plated
through holes. The solder has failed to rise in the hole or wet across
the surface of the pads. In this case there is no benefit from the
legend and
new design rules need to be applied.
 |
| Figure 6: The legend on this PCB has contaminated the
top of the plated through holes. |
Figure 7 shows poor wetting of the surface of the
pads and is likely to be due to the thickness of the tin/lead coating.
Solder levelling often leaves a thin deposit on the surface of the
pads and on the edge of the hole. This defect is often referred to
as the weak
knee effect,
where the solder fails to wet over the knee of the hole and on to the
pads. Poor hole fill can also be due to the pre-heat operation being
set too low
or poor flux application. In both cases a check on the process parameters
should eliminate the problem.
 |
| Figure 7: An example of the 'weak knee' effect. |
Wave Soldering Defects:
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Inconsistent or Poor
Hole Fill | | | |
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