In PCBA manufacturing, utilizing a proper reflow oven profile which takes into account solder chemistry, componentry, board thickness and layers, and more will directly impact the quality of finished circuit board assemblies, and certain quality issues serve as indicators that the profile needs to be adjusted. Knowing what issues to look for is critical so you can adjust the profile right after they are found, leading to huge cost savings from avoiding heavy post-production cleaning and rework. Here are some of the common issues to look for, and what these indicators are telling you.

Tombstoning: to reduce tombstoning, you must minimize the thermal gradient between the pads prior to reflow. This can be accomplished by slowing the ramp rate from ambient to peak temperature, allowing the PCBA to evenly rise in temperature. You can also try instituting a small soak (or shoulder soak) just below the melting temperature of the alloy.

Solder Balling: To prevent solder balls, it is recommended to not exceed a ramp rate from ambient to peak temperature of 1-1.5°C/second. When solder paste is heated too quickly, solvents in the flux vaporize violently, creating small explosions which leave solder balls or paste aggregates isolated from the solder mass with no ability to return to the solder joint. However, if the ramp rate is too slow, the flux can spread out excessively and carry solder particles along with it. It is critical to make sure your ramp rate is right in the sweet spot.

Residue discoloration: Multiple reflows can darken the flux residue which can result in a more difficult residue to remove. The flux residue is directly affected by temperature, so a reflow profile with a shorter TAL, lower peak temperature, faster ramp rate, and no soak provides the best results.

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