April, 2011
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tech.com
What to Look for in Lead-Free Selective Soldering Equipment
By Alan Cable, President, ACE Production Technologies Inc., Spokane Valley, WA S
elective soldering is a flexible, adaptable process that increasingly applied to an ever-
is
widening range of soldering tasks. However, the selective soldering
control module. The monitor and con- trol module should typically be able to maintain solder wave heights to within ±0.005-in. (0.127mm), which is critical when selectively soldering the smallest, tight pitch components in high-volume automated produc- tion environments. They are particu- larly effective when working with the smallest wave nozzle sizes, under
6mm down to 1.5mm, and selectively soldering tight pitch component areas.
The ability to apply continuous,
real-time top-side pre-heating during the selective soldering process is crit- ical to achieving good soldering results when processing high-mass assemblies, because top-side (inter- nally mounted or installed) integral
preheating promotes the draw of the solder through the barrel to the top side of the board, enhancing the for- mation of solder fillets on the top side. Using internal continuous pre- heat during the selective soldering process improves thermal distribu- tion and solderability of difficult assemblies.
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Page 59
Dual nozzles add versatility.
process itself is complex. There are many selective soldering machines available on the market, ranging from expensive automated systems to smaller benchtop models with lim- ited automated capability. Most users fall somewhere in
the middle, seeking semi-automatic machines or machines with in-line capability and some medium degree of product handling capability. There are many additional features and options available, which should be considered, based on the demands of the application. Some of them are described here, with their uses. This way, the prospective selective solder- ing systems user can get an idea of what might be advantageous to spec- ify when looking at selective solder- ing machines. A dual nozzle configuration
brings significantly greater flexibili- ty and efficiency to the selective sol- dering process. Dual nozzles allow two differently-sized nozzles to oper- ate in tandem, each one individually programmable, to handle a wide range of component types and sizes on an individual PCB assembly dur- ing the selective soldering process. As an example, an individual board with differently-sized components can be processed in a single pass through the machine, rather than two or more — if different-sized noz-
Nitrogen peel-off jet improves fine-pitch
selective soldering results, especially when using lead-free solders.
zles are needed to process a single board. This eliminates the need to change nozzles in mid-process, and both nozzles operate within a single soldering sequence program, for sim- pler and easier setup and operation. An operator can process a small
component using a 3 or 6mm nozzle, for example, as well as a larger multi-row connector on the same PCB using a 12mm or 18mm nozzle, all with the same program, in a sin- gle pass, without manual nozzle changes.
Wave Height Monitoring One very important process con-
trol is a wave height monitor and its
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