Feasibility of Soldering Fine Pitch THT Components

One of the major trends in circuit board assembly is the drive to smaller components and pitches. Where the focus is on SMD (Surface Mount Devices) and also THT (Through Hole Technology) the designers have the intention to go smaller and smaller. The result is less space on the boards but with increased functionality. The Roadmaps from IPC and iNemi mention a minimum pitch of 40 mils (1.00 mm) in the near future. The physical properties of the lead-free alloy, flux and solder mask give the engineer problems to set-up a consistent and robust soldering process for these smaller devices.

The method of soldering THT components depends on the number of components to alloy and available time on the machine. For low volume products a sequential method (point to point soldering) is most likely the most cost effective way. Available methods, apart from hand soldering, are robot, laser or selective soldering using a mini wave nozzle. For high volume assemblies a simultaneous soldering method is preferred because of the shorter cycle times. There are three main ways that THT components could be soldered. The first is in a reflow oven (using Pin in Paste technology). The second would be in a traditional wave solder machine using pallets that cover the small SMD’s. Final solution could be a selective soldering application which would involve dipping the complete assembly on to a dedicated nozzle plate.