Speedline Technologies paid host to SMART Group delegates for a packed day of hands-on process demonstrations and theory on how to achieve Zero Defects. "Eliminating soldering defects starts with the knowledge that the process has its limits and not all soldering defects can be eliminated with the soldering equipment". "There are many process defects which can be overcome with correct process control but design, PCB specification and component design issues can have a significant role in generating problems for the engineer" stated Bob Willis Speedline Technologies process training consultant.

Bob Willis has been running process training with Speedline Technologies since its creation and for 10 years with Electrovert. He runs his own training and consultancy company based in Chelmsford and is Technical Director of the SMART Group.

25 engineers attended the SMART Group workshop which started with an introduction from Phil Stokes, Sales Manager with Speedline.

During the morning Bob Willis covered the basic wave soldering process, deign rules for conventional and surface mount layout. The most common defects seen on surface mount boards are solder skips on SOT23, chip components and solder shorts on SOICs and QFPs.

The causes and cures for the following defects were covered during the day

You can solve these and similar process issues on-line with the SMART Group www.smartgroup.org and enter the members area for the FREE online Wave Solder Defect Guide.

Following a very enjoyable lunch provided by Speedline, Phil Atkinson, Applications Engineer with Speedline took over the second half of the day with support from Bruce Seaton. Wave Solder test boards were used on one machine while a surface mount boards were processed on a second machine showing the different results that could be obtained with and without nitrogen.

Phil Atkinson stepped through the process and the changes that have taken place with equipment over the last few years.

SMART Group's Introduction to Wave Soldering and Defect Guide CD-ROM was also available for delegates' interactive use during the afternoon session. It is an ideal resource for shop floor reference for engineering and production staff alike. Three lucky delegates won CD-ROMs in a lucky dip at the end of the day, the CDs were sponsored by Speedline Technologies.

The SMART Group website www.smartgroup.org hosts an online wave solder defects guide in the members section of the site. Its an ideal resource for engineers and staff alike to solve problems on-line.

During the day delegates discussed their specific process problems and boards where displayed for review. The problems seen consisted of skipped surface mount joints, solder shorts and solder mask staining.

In the case of skips the most common reason is gassing on the base of the board during contact with the solder wave. This is either due to gassing from the solder mask or too much flux or incorrect pre heat. The examples in question were processed on a machine with only one wave. Ideally a machine with a double wave will give the best performance on any machine. A chip wave followed by a standard wave is accepted by most people as being the optimum.

Solder shorts on 0.020" pitch SOICs, resistor network and Pin Grid Arrays ("PGAs")

Ideally the 0.020" SOIC packages and surface mount resistor networks should not be on the base of the board. This design will always give a lower yield during wave soldering. The PGA should be suitable for wave soldering but either a change in orientation or an increase in the amount of flux applied should improve the drainage.

Staining of solder mask

The discoloration of the solder mask was either due to the pallet protecting areas of the board or the mask was changing colour. This is common where the heat and flux produces a surface effect on the solder mask. It can also be related the degree of cure of the mask or simply a function of that material.

Another very enjoyable day organised by the SMART Group and Speedline Technologies which is hoped will be repeated in the near future. Many thanks to Speedline for hosting the day, you can visit them on www.speedlinetechnologies.com or visit them at Productronica 2001

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