Importance of the reflow oven in SMT process
Electronics industry has seen a systematic shift from the through hole technology (THT) to surface mount technology (SMT) in past decade. This shift is mostly to induct automation, reduce dependency on skilled resources, increase through-put, achieve highest quality and reduce overall cost.
In a PCB assembly process, reflow oven is the most important machine to weld surface mount components to PCB. Currently, it is extensively used across all PCB assembly factories for building electronics devices such as mobiles, hand held devices, LED lights, automotive control units, aeronautics, defence sectors, control circuits in industrial automation, etc.
An ideal Surface Mount Technology (SMT) consist of four parts: solder paste printing machine, SMT machine, Reflow oven and testing machine at the end.
Solder paste printer apply solder paste to PCB as per required thickness and pass it to SMT machine for mounting SMD components. Post SMT process, the PCB is passed through the reflow oven where the magic of welding/soldering happens in a computer temperature controlled environment.
Lead and Lead free welding /soldering:
Soldering paste with lead (e.g. Sn63Pb37) has 63% tin and 37% lead and melting point of around 183°C (361°F). For a good weld the thickness must be in between 0.5 to 3.5 μm for the components. The inter-metallic compound formation happens at 195 (383°F) to 200°C (392°F) which is higher than lead based welding.
Due to the RoHS guidelines, there is a demand in the industry for lead free solder paste. However, lead free solder paste needs higher temperature for welding. The lead free solder paste (e.g. Sn96.5/Ag3.0/Cu0.5) has melting point at 217-220°C (423-428°F). The maximum temperature of electronic circuit designed to withstand is about 240°C (464°F). This makes the temperature difference gap very close when the board is passed though reflow oven.
Due to computer controlled temperature for all zones ensure that the welding process is achieved as required and not crossed the maximum withstand limit of components.
At ElectroTrail, we have a computer controlled temperature eight zone reflow oven attached with industry best SMT line.
