SMART Group

Willy Campbell (Chairman SMART Group Scotland) gave a brief introduction, ran through the agenda for the day and thanked all the delegates and the tabletop exhibitors for contributing to the event.

Lead Free Surface Finishes - presented by Ian Hood (ZOT Engineering).

Ian explained that ZOT engineering had been looking at Lead Free board finishes for a number of years for ROHS compliance. ZOT’s board manufacturing trend over the last 6 months showed that lead free HASL finish was really taking off and currently 50% of HASL board production was lead free. Customers converting to lead free HASL boards are finding that this causes minimal disruption to their process “a slot in replacement”.

From both a ZOT and a customer stand point this maintaining both processes and managing stocks of standard and PB free finish boards was difficult, requiring marking of packing and the individual boards. The most common issue highlighted is the poorer wetting of the pads on emersion silver, tin and gold finishes, HASL finish gave the best results. Although the wetting on pb free finish boards was not as good as conventional boards, they still satisfied the IPC inspection standard. ZOT gave a guide as to the cost of using lead free boards in comparison with conventional boards, HASL being the cheapest and gold being the most costly.

WEEE and RoHS legislative update - presented by Martin Tarr (Martin Tarr Associates).

Martin gave some background info as to why we have WEEE and RoHS legislation and the differences between them. During the presentation, it was explained that there will be local variations of legislation enforcement depending on the country. In the UK the National Weights & Measures Lab are contracted to enforce the legislation and if found to be non compliant you will have 28days to respond. Manufacturing companies need to be able to provide evidence that they are compliant with the legislation, otherwise it will be illegal to sell the product after July 1st 2006.

The grey areas highlighted were exemptions and exclusions. Military or High Voltage products are excluded and Medical, monitoring and control, spares and upgrades could be exempt from this legislation until 2009.

The background to LEADOUT was also given. It is a European funded initiative to assist in the transition to remove lead from products. A consortium of bodies and manufactures are being funded to conduct tests etc to eliminate lead from products. The consortium members are fixed, but their reported findings are free. Anyone wishing to know more can register online. www.leadoutproject.com

A Users View on Lead Free Thro Hole Soldering - presented by Steve Mainwaring (Solectron Scotland Ltd).

Steve shared with the audience the results of the through hole soldering tests conducted by Solectron on a variety of surface finishes, with images showing the impact of the issues found. Barrel fill was the biggest issue seen, due to a combination of surface finish, preheat, flux, solder temperature, design and pin surface. Another issue shown was the dewetting of paste from the pad to the component due to the board surface finish.

Steve highlighted that it was difficult to ensure that all components met the required temperature spec, Solectron used component shields to protect the occasional component which did not meet the temperature rating, but this is only a solution for isolated cases.

Rework for lead free boards was an issue, trials showed that 35seconds of heat during a rework process would completely destroy the pad due to Copper dissolution, therefore you only get one chance at repair then the board is scrap.

Lead Free Microstructure Comparison - presented by Stewart McCracken (MCS).

Stewart explained that Microstructure Analysis can clearly show an issue, but understanding the interactions between materials and solder joint metallurgy will help route cause issues and ultimately control quality.

Images were shown comparing a selection of joints, shiny, smooth, dull, tears and voids, understanding why they occur can help the problem be addressed or even ignored.

One example shown was dewetting on 2nd side reflow due to erosion of emersion tin surface, using Microstructure Analysis the route cause was determined. In this example, the first side reflow had caused an unsolderable surface on 2nd side due to the Cu/Sn intermetalics.

A second example shown was joints with large brittle crystals, analysis showed that these were iron crystals. The route cause was determined to be Iron/tin intermetalics due to the solder pot coating being damaged and iron being leached from the stainless steel solder pot. This problem was seen very shortly after the pot damage occurred.

SMART Group Message – Paul Salmon

Willy Campbell introduced Paul who spoke briefly about the SMART Group and thanked everyone for supporting the event.

Lead Free Alloys - presented by Ron Gow (DKL Metals Ltd).

Ron provided some background information as to why legislation was being introduced forcing manufacturers down the lead free path. A complete list of lead free solder alternatives available was presented and the advantages and issues associated with each of them were highlighted. Ron gave details on the top few recommended alloys and some of the pros and cons of using these.

In choosing an alloy the approached recommended was to determine the priority, e.g. maximum temperature or time above eutectic or appearance, as this will make the best selection clearer.

One of potential issues highlighted was copper erosion and leaching, results of a copper pin test verified the Solectron conclusions and photographs showing the damage to a stainless steel solder bath were also shown.

Lead Free SMT A Users View - presented by Derek Mair (Micron Europe Ltd).

Derek gave a brief history of Microns lead free experience and the issues they have encountered since its introduction in 2003. Material management created a problem, both getting lead free parts that withstood the 260deg spec and also avoiding mixing inventory of parts during the transition to lead free.

To obtain RoHS certification a manufacturer must be able to prove that they are compliant, this necessitated additional documentation to demonstrate compliance.

The biggest problem experienced was tombstoning, Micron tried a few things but found the key was tighter control of placement accuracy. Another issue seen was that the duller solder required machine part geometries to be changed for vision processing, the control of these PD’s was yet another issue. The reflow profile not only required larger ovens, but a tighter process window was required and so control was more important.

Tin whiskers was a big concern, but it did not present a major issue so long as material properly stored.

On behalf of the SMART Group, we would like to thank all the speakers for their presentations and the vendors (ZOT, DKL, Kester and Park Heath) who supported the table top exhibition at the event in Livingston on March 2nd.

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