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ACW Technology has helped industry consultant Bob Willis with a test trial for German solder manufacturer Cobar Solder Paste.

The trial involved production of test boards aimed at comparing through-hole, intrusive reflow solder joints using SN100C lead-free solder paste – an RoHS material which, due to its composition, has a higher reflow temperature than standard RoHS solder paste.

For the trial, Bob needed vapour phase reflow using a higher-temperature vapour phase liquid than normal.

ACW’s Tonypandy, South Wales site uses this type of fluid.

After successfully reflowing Harting 96-way connectors on multilayer boards using ACW’s vapour phase system and 240C boiling solvent, each board was inspected for through-hole fill and soldering quality.

They were then X-rayed to examine the level of voiding using a DAGE system.

Microsections were also taken from selected joints.

All the samples exceeded the quality levels of IPC 610D, with 100 per cent fill and positive solder fillets.

There was very little evidence of voiding in the joints, and the microsections showed satisfactory wetting to each of the different surface finishes.

Peter Barton, senior process engineer at ACW says: ‘We use 240C vapour phase fluid because some of the assemblies we process have heavy metal fixturing, which is a large thermal mass to heat.

‘The extra 10C over the typical temperature used for RoHS soldering helps us to maintain normal profiles.

‘We also have a vacuum option on our machine for some soldering applications.

‘The higher-temperature fluid ensures that when we use the vacuum the solder is still molten at that stage of the process.

He continues: ‘This extra capability is not at the cost of flexibility.

‘Lower-temperature processing for non-RoHS applications is also still possible by tailoring the machine heating power and dwell parameters in other reflow programmes.

This is important to us, as we have a number of MIL/Aerospace clients that still require this.’

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