Title General guide to solder balls in wave soldering—now you see them, now you don’t
Bob Willis
General guide to solder balls
in wave soldering—now you
see them, now you don’t
There are two types of solder balls gener- ever tried microsectioning solder balls on from outgassing due to the flux volatile not
ally seen after wave soldering. They can a solder mask surface you will know how being dried prior to wave solders contact.
be referred to as consistent/repeating or difficult it is. Loosing your balls can be a The solder literally explodes on the surface
random balls. Obviously there are lots of big problem to some!!! of the wave. The solder particles then
theories on how they form and attach/ bond to soft surface of the solder mask or
bond to the surface of the solder mask. Im- random solder balls remaining flux.
ages below are taken from the Bob Willis The balls vary in size and are positioned Seeing balls on the top side of the
archives and show the many sides of ball randomly on the base of the board. Some board generally indicates an increased
formation. evidence of solder balls can also occur on severity of the problem. They normally
Figure 1 shows microsections of ball the top surface of the board after wave blow through tooling hole cutouts on the
location on a solder mask surface. Now or selective soldering. Basically the solder surface of the board. If the copper plating
you seen them, now you don’t. If you have balls have either formed due to spitting or in the hole is poor, solder balls can be
ejected out of plated through holes as the
water vapour in the board expands; in this
case flux is not the root cause.
When there is a lot of evidence of
random solder balls from wave contact,
surfaces around the wave ducting will
be covered in small balls. There will also
be evidence of balling on the inside top
surface of the hood over the wave and all
over the pallets.
If the wave is being pumped higher
than 5-6 mm to accommodate other parts
Figure 1. Microsections of ball location on a solder mask surface.
of the process, the solder returning to the
solder bath can produce solder balls. This
can be seen on an air system directly after
de-drossing the solder surface and less
so after the solder start to form an oxide
layer. The oxide on the wave suppresses
the solder from bouncing back from the
surface. This is seen more commonly on a
nitrogen wave.
The use of an air knife after the wave
can generate solder balls on the top side
of the board, with excess air or nitrogen
pressure or incorrect angle of the knife
to the board. This normally occurs when
Figure 2. Random solder balls on the surface of two different solder mask coatings.
engineers are trying to increase the perfor-
4 – Global SMT & Packaging – February 2009 www.globalsmt.net
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56