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Going Lead Free with Vapor Phase Soldering
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Authored By:Andreas Thumm IBL-Lottechnik GmbH Koenigsbrunn, Germany TranscriptEveryone is aware of the move to lead free. Most all components are typically available in lead free quality, so why hasn't everyone changed over, how can the challenges be overcome? A big concern in this transition process is reflow soldering. The process temperatures for lead free applications became much higher. Related with this is more stress for all the components. It affects the quality and reliability of the electronic units and products. Many companies are running a mix of lead free components with a tin-lead solder paste. This allows them to stay at the same and approved low process temperatures, but it's not a long-term solution. Many companies have not found the right solutions to change over to lead free. In some cases vapor phase reflow soldering can be an answer. The heat needed for great solder results in vapor phase soldering is only a few degrees above the melting point of the solder pastes. Vapor phase systems are available from table top machines up to big inline units. This paper explores options for using vapor phase systems for lead-free reflow soldering. SummaryAs of today, the electronic industry is aware of the requirements for their products to be lead free. All components are typically available in lead free quality. This comprises packages like BGAs with BGA solder balls to PCB board finishes like HASL. The suppliers are providing everything that is needed. It is harder to get the old tin leaded (SnPb) components for new applications today, than lead free ones. So why has not everybody changed over fully yet and how can the challenges be overcome? A big concern in this transition process is reflow soldering. The process temperatures for lead free applications became much higher. Related with this is more stress for all the components. It affects the quality and reliability of the electronic units and products. Many companies are running a mix of lead free components with a SnPb solder paste. This allows them to stay at the same and approved (low) process temperatures. It is no long-term solution, because it is not lead free. But it is still accepted from customers and legislator yet sometimes it is tricky. The mix of the different solder that are supposed to form one solder joint, do not mix as well as expected or known from the past. Other companies have changed over to lead free completely. They were facing more or less trouble with the typical lead free problems, higher temperatures, smaller process windows, decreased wetting, and so on. Some products have a lower first pass yields and more defects. Some simple products though show no problems at all. The majority of solder paste produced and used in production is still the old tin lead solder paste. Automotive industries, aviation, military, science and medical industries are keeping their approved processes as long as they have no adequate or better solutions. Low PPM failure rates and highest reliability are standards and a risk or drop in quality is absolutely not acceptable. Many tests have to be made to approve new materials and processes. Many companies have not found the right solutions to change over to lead free yet. Vapor phase reflow soldering can be an answer for them. ConclusionsKeeping the process temperatures as low as possible and the absence of oxygen during soldering will result in excellent quality applications and products. Modern Soft Vapor Phase systems perfectly combine these attributes. Equal temperature distribution and the physical limitation of maximum temperatures are automatically provided. Double sided and densely packed PCB boards with BGAs, LEDs with metal core boards, ceramics and GCB units can be soldered perfectly lead free. Power electronic units, as they appear with new electric and hybrid technologies in the automotive industry work excellent on vapor phase systems. The heat needed for great solder results in Vapor Phase soldering is only a few degrees above the melting point of the solder pastes. Vapor Phase ovens are available from table top machines up to big inline systems. The size of a Vapor Phase system is not related with the solder profiles it can produce and the profile is done in only one chamber. The energy cost for a VP system is only a third comp ared to a convection system. Negative effects like tombstoning and voiding can be influenced with a good soldering profile in today's Vapor Phase systems. Other reflow methods require more than 30°C - 50°C excess heat for the same task due to their lower heat transfer rate Initially Published in the SMTA Proceedings |
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