Reflow Soldering


0-ppm fault strategy with vacuum reflow soldering

Absolute quality in LED

When highly sophisticated lighting technology assemblies for the automotive industry or complex microprocessor controls for machine and plant engineering are required, there is one name that quickly comes to mind: Herkules-Resotec. The company, which is based in Baunatal in the heart of Germany, develops, programs and manufactures customer-specific solutions for OEM and serial products – at automotive level, in other words: with 0 ppm fault strategy. Since July, the northern Hesse company has been relying on a further soldering plant from system supplier Ersa to help them achieve this: a vacuum reflow soldering system EXOS 10/26.

Zero parts per million as target and requirement leaves little room for compromise. Herkules-Resotec doesn’t even need that; rather, the EMS service provider has taken the high requirements and incorporated them in its own philosophy: “Our strength is the implementation of customer ideas in electronics in such a way that they result in successful products on the basis of absolutely reliable functionality,” says Günter Reginka, one of three managing directors at Herkules-Resotec. The linchpin of this approach are state-of-the-art SMD equipping lines, where assemblies are manufactured in reproducibly consistent top quality, independent of the batch size – from the individual prototype through to large-scale production. Customers from the automotive industry in particular value the reliability of the assemblies from Herkules-Resotec – but industries such as general machine and plant construction, print post-processing, medical technology and industrial electronics also benefit.

The core competence of the Automotive Division in Baunatal is LED processing – the 80-strong Herkules-Resotec team manufactures everything from daytime running lights through indicators, brake lights and rear lights to ambient lighting – all in top quality and in large-scale production. Products for industry include high-mass components for power electronics such as MOS-FET (metal-oxide-semiconductor field-effect transistor) and IGBT (insulated-gate bipolar transistor).

For these, the production of the solder connection in the reflow soldering process is controlled centrally and reliably, because the development of the components with their increasing miniaturisation and enhanced functionality makes high demands on the characteristics of the solder connection. In addition, the entire process chain and thus further factors must be monitored, starting from the solder paste through the stencil printing process to the reflow soldering furnace in combination with the parameters used. Herkules-Resotec, which has been manufacturing electronics since 1985, has first-class production conditions – not least due to the energy-optimised production hall with ideal material and work flows newly opened in 2018.

Major influence: void share in the soldering spot

Yet back to the assembly: alongside the electrical connection, heat dissipation behaviour is decisive for LEDs and power components. High-power LEDs generate a very high energy density in operation, which must be dissipated mainly via the surface of the soldering spots into the printed circuit board. The main factor of influence is the void share of the soldering spot – consequently the share of gas inclusions which form in the soldering spots during remelting of the solder paste. Depending on size and position, these “voids” reduce the cross-section of the joint, which leads to significantly reduced heat dissipation in the case of BTC power semiconductors or LEDs. The faulty spots contained are thus not good heat conductors (in the worst case this leads to component failure), which is why the void share must be limited to a minimum. Component manufacturers specify thermal limit values in their data sheets, which are used by developers to define the maximum permissible void shares of a soldering spot to avoid exceeding the maximum temperature of the components in operation. The common upper limit is 25% maximum – if the permissible temperature is exceeded, components can become damaged and the service life of parts can be shortened. This is all the more probable the closer to the limit range of their application the components are operated. Better dissipation through a reduced void share to between 10 and 15% counters this effect. The void share can also be pushed to less than 5%, although the process time is then extended accordingly.

Herkules-Resotec and Ersa: high know-how potential

This wide range of requirements and considerations convinced Herkules-Resotec to invest in a reflow furnace with vacuum soldering chamber: the Ersa EXOS 10/26 with eleven conventional heating zones (above and below), three heating circuits for the vacuum chamber and four cooling zones (above and below). The modular system impressed through several notable features, including the four-segment conveyor system with infeed, pre-heating zone with peak zone, vacuum module and cooling module, each with its own conveyor. The medium-wave emitters in the vacuum process were also convincing; they are used to achieve optimum stable temperature profiles – the heat transfer of the EXOS, based on an advanced technical development of the tried-and-trusted Ersa multijet convection technology, guarantees a minimum ΔT with lowest possible energy consumption. A stable, easy-to-replace roller conveyor which requires no lubricant is used in the vacuum chamber itself – best preconditions for low-maintenance transport and zero lubricant precipitation on the assembly during the vacuum process.

The decision in favour of the Ersa reflow system is thus completely understandable, particularly since the entire soldering technology for electronics manufacturing at Herkules-Resotec is from Ersa – starting with a wave soldering system of the type EWS 330 before systems from the HOTFLOW 2 series were ordered and installed in 2004. From 2014 onwards, a HOTFLOW 3/14 followed every 2 years before the EXOS 10/26 was added to the Herkules-Resotec machine park. “Thanks to the long years of cooperation and trusting partnership going back more than 20 years now a high degree of know-how potential has developed between the two companies, and the decision in favour of the new Ersa EXOS vacuum reflow soldering system was easy for us to take,” says Ulrich Jonas, one of the other two managing directors at Herkules-Resotec. Thanks to intelligent features – above all the vacuum chamber as a component of the peak process area – particularly profitable “void-free” production is possible with the Ersa EXOS 10/26. The void rate of an LED assembly produced on this was able to be reduced from 8.5% before (largest individual void: 2.2%) to an impressive 0.5% (largest individual void: 0.3%).

As a pilot user, Herkules-Resotec played a major part in the development of the reflow furnace and provided important information about productivity, traceability, service and maintenance from the operator’s point of view. In concrete terms with a view to productivity, this means that Herkules-Resotec places great value on flexible utilisation of the production lines. In other words, the vacuum soldering system must also be suitable for the classic reflow process and achieve the same throughput. The process time is slower during operation with vacuum chamber; this is compensated by the longer version of the furnace model compared with other reflow furnaces at Herkules-Resotec. In addition, the vacuum level to be achieved is decisive – the higher this is, the lower the void rate. Data were generated during various series of trials to achieve optimum tailor-made results for the respective product. Furthermore, the EXOS 10/26 has outstanding maintenance friendliness: the entire vacuum unit with pump, filters and valves is integrated in the machine room for the most part, so that an additional footprint of less than 2 m2 is required – any maintenance work due can be performed easily outside electronics production, since the complete unit is mounted on a separate, mobile module that can be moved easily out of the system thanks to quick-release locks. This reduces downtimes to the absolute minimum necessary.

Data basis for transparent production

Another absolute must for Herkules-Resotec was the subject of traceability – the Management Execution System (MES) makes traceability down to component level and through to the process parameters used possible. For the EXOS this includes the vacuum level achieved and the process times used as well as the temperatures of the furnace zones – all these data are provided at the MES data interface. Another important requirement on data generation was Predictive Maintenance, where the maintenance intervals are adapted to the throughput and performance of the reflow furnace. EXOS works in just the same way as a car that reminds the driver that an oil change is due: the system “knows” exactly how long the vacuum pump was active and indicates when an oil change is due. The aim here is not as much to avoid costs, rather to secure reliable operation.

“A high system availability is key for our three-shift operation. Service and maintenance are extremely important. Together with Ersa we have carried out numerous optimisation processes within the course of the nine months trials – including ensuring that the elements to be cleaned fit into the existing washing system,” says Managing Director Günter Reginka, who, alongside his whole electronics manufacturing team, is satisfied all round with the sixth Ersa soldering system to be installed. “The EXOS project between Herkules-Resotec and Ersa showed once again how valuable such a long-term partnership is – we would like to say a special thank you to the Herkules-Resotec team for the successful implementation, which will certainly benefit many customers,” says Ersa General Sales Manager Rainer Krauss, summing up a remarkable bilateral project.

Highlights Ersa EXOS 10/26

  • Perfect synchronisation and transitions thanks to four-section conveyor
  • Maintenance-friendly and lubricant-free roller conveyor in the vacuum module
  • Optimum access to the vacuum chamber through drives from above
  • Optimum temperature profiles through medium-wave radiant heaters in the vacuum module
  • Maximum machine availability thanks to fast removal of the conveyor unit in the vacuum module
  • Innovative Ersa SMART ELEMENTS cleaning system

Article Author

Michael Haas Product Manager Reflow, Ersa GmbH

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