Tombstoning is laid to rest
Sep 10, 2003
Parkheath, one of the UK's leading suppliers of electronics assembly equipment and materials, has introduced an outstanding lead-free no-clean solder paste from soldering specialist Cobar. The new 325-Xm3S Solder Paste with S9M alloy has been specifically developed to meet the demands of lead-free manufacturing. It not only delivers optimum solder joint quality, but it possesses an amalgam of alloy ratios that eliminate tombstoning and greatly reduce solder balling and mid-chip beading defects that are more likely to occur when reflow soldering at the higher temperatures demanded by lead-free alloys.
"As assemblers become more involved with lead-free soldering, if they are not careful in the selection of their paste they will find that the incidence of tombstoning and solder balling increases," says Terry Morgan, Managing Director of Parkheath. "However, Cobar understand this and have developed a paste whose thermal stability at the higher temperatures and soldering performance have been tuned specifically to deliver high quality results in lead-free manufacturing processes."
In fact, Cobar's proprietary synthetic long-chain polymer chemistry gives the paste greater thermal stability at elevated temperatures than any competing product. Its flux chemistry increases wetting performance on lead-free pad finishes, wetting out to the pad geometry and component leads better than any other lead-free paste. This ability to wet-out onto lead-free pad finishes provides a high value of solder mobility during reflow, when the paste also displays excellent hot slump characteristics and reduced voiding.
S9M contains alloys of tin, silver and copper with an overall composition of 86%, 3.3% and 0.3% respectively by weight, and provides outstanding performance during all of the printing, reflow and post-reflow stages.
The paste has a wide print-process operating window, being suitable for printing speeds from 20mm/s all the way up to 120mm/s. Its particle chemistry is tightly controlled during manufacture to provide a smoothness that greatly improves the print definition and significantly lowers print defect rates.
The paste offers a stencil life of more than eight hours working time, together with a long open and tack time. This means it can easily stay on the stencil for more than a typical manufacturing shift without a reduction in performance, keeping downtimes to a minimum and boosting productivity.
Downtime is also lowered further as the paste reduces smearing as well as the need for under stencil cleaning, increasing the run time before the stencil has to be removed for cleaning.
Reflow soldering leaves behind only a minimal clear, colourless residue, due to the purely synthetic polymer chemistry, absence of rosin and the colophony-free resin flux medium. S9M, as with all of Cobar's paste systems, has been proven to reduce reflow oven contamination by up to 50% compared against other leading solder pastes.
The paste is available in all types of packaging format's including ProFlow, Rheopump, Semcos, pots and others ˆ and Cobar is qualified to ISO and AQAP standards.