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42 SMT Magazine • April 2015 abstract The drive towards fine-pitch technology also affects the soldering processes. Selective soldering is a reliable soldering process for THT (through-hole technology) connectors and of- fers a wide process window for designers. THT connectors can be soldered on the top and bot- tom side of boards, board in board, PCBs to metal shields or housing out of plastic or alumi- num and are today's state of the art. The materials used to make solder connec- tions require higher temperatures. Due to the introduction of lead-free alloys, boards need more heat to get the barrels filled with solder, which not only affects the properties of the flux and components, but the operation tem- peratures of solder machines become higher. A nitrogen tunnel wave solder machine requires a temperature control in the tunnel to prevent overheating, and advanced systems are avail- by Gerjan Diepstraten VITRonICS SolTEC Position Accuracy Machines for Selective Soldering of Fine-Pitch Components able that insert cold nitrogen. The closed tun- nel wave soldering process has a wide process window and is not sensitive to small changes in environmental conditions; the same goes for wave solder machines that have nitrogen blan- ket systems over the wave. Improved preheaters will bring sufficient heat in the assembly and exhaust systems are adequate enough to main- tain required process conditions. The nitrogen will improve the soldering and minimize dross amounts at these elevated solder temperatures. Selective soldering is a different process. Compared to wave soldering there are addi- tional process parameters that are affected by the higher temperatures. Solder joints have to be made close to SMD pads or components. An off-set of 0.5 mm may result in solder skips or re-melting SMD components. Additionally, the higher temperature may cause warpage of the board, which also affects the position accuracy FeAture figure 1: (above) example of selective soldering metal shielding.