The third stage, reflow or peak temperature, is the critical melt period where the solder liquefies and surface tension pulls the joint into formation. This creates a narrow process window where the solder is fully liquid but the components and substrates remain within their safe thermal limits.
Building Reliable Reflow Profiles: Mastering the Melt Phase and Process Window
Insufficient time or temperature during the melt phase results in cold joints, where the solder is grainy and fails to create a robust mechanical bond. For a common SAC305 alloy, the peak temperature is typically held between 215°C and 235°C above the liquidus temperature of the paste, which is often around 183°C for lead-free materials.
Exceeding this window, even by a few degrees for a few seconds, can risk delamination of the board or damage to sensitive semiconductor devices. Common Defects Linked to Profile Errors Deviations from the optimized reflow profile manifest in a variety of defects that compromise reliability.
Crafting Stable and Reliable Reflow Profiles for PCBA
Conversely, excessive heat or a too-extended melt period can lead to solder balling, where the surface tension of the molten paste forms small, non-wetting spheres rather than a smooth fillet. Oxygen Inhibition and Process Control A critical chemical factor in profile optimization is the management of oxygen inhibition within the reflow oven.
More About Solder reflow profile
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