ACW aids Bob Willis and Cobar Solder Paste in lead-free trials

The trial involved production of test boards aimed at comparing through hole, intrusive reflow solder joints using SN100C lead-free solder paste - a RoHS material, which due to its composition, has a higher reflow temperature than 'standard' RoHS solder paste. However, through hole reflow can be challenging from a thermal profiling point of view due to the mass of the connector body. Previous work on convection reflow has shown joint formation exceeding the requirements for professional electronics at 245ºC. For the trial Bob needed someone with vapour phase reflow using a higher temperature vapour phase liquid than normal. ACW’s Tonypandy site use this type of fluid and was happy to help. After successfully reflowing Harting 96 way connectors on multilayer boards using ACW’s vapour phase system and 240ºC boiling solvent, each board was inspected for through hole fill and soldering quality. Each board was 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% fill and positive solder fillets. Bob Willis said: “I had already run some boards successfully on a convection oven but wanted to run the same board and paste with vapour phase. The majority of vapour phase systems in the UK run a fluid with a boiling point of 230ºC for lead-free, which would not be suitable for the paste. I was delighted to find out about ACW’s 240ºC fluid and when they agreed to help. Without ACW’s facilities I would have struggled to complete the trial successfully.” Peter Barton, Senior Process Engineer at ACW comments: "We use 240ºC temperature vapour phase fluid because some of the assemblies we process have heavy metal fixturing, which is a large thermal mass to heat. The extra 10ºC 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."