Robotic soldering of lead free alloys

摘要

The wave soldering process of Electronic Assemblies with lead-free materials has become one of the most expensive factory process to maintain. Cost detractors include: High dross formation of Lead Free materials in the molten wave soldering pot, (dross waste can approach up to 76% of SAC alloy bar used). Decreased % of Plated-Thru-Hole (PTH) soldering components. Reduced production volumes. As a result, many companies have started to migrate toward a robotic soldering process as an alternative cost approach. Contrary to common belief, robotic soldering is not a simple direct drop-in replacement for manual soldering. Robotic solder consistency and reproducible soldering quality are not a given without careful process design considerations. The Robotic Solder process design must address: Printed Circuit Board Assemblies (PCBAs) with high heatsink count. Thick PCB boards with high layer count and large thermal mass. Robotic soldering equipment, utilizing a solder iron concept, faces challenges of high flux residue levels, negative wetting angles and, in many cases, insufficient barrel fill. The fundamental challenge of the robotic soldering process is achieving adequate heat transfer to the solder joint during the soldering process. Process variables include: Solder iron tip selection. Fixture positioning accuracy. PCB thickness, layer count, circuit layout pattern and thermal mass of the substrate. PCB hole diameter to component lead diameter ratio. Relative component pin position. This paper discusses the differences between manual soldering and robotic soldering with a solder iron, highlighting the variations in heat transfer efficiency. An experiment is described which introduces PCBA preheat as the second source of heat energy transfer to improve the process window margin.