Last week, we discussed how to design for reliable PCB soldering, covering pad geometry, thermal balance, component spacing, and surface finish. This post continues that discussion with a few practical soldering tips that are easy to overlook but important for long-term reliability.
A PCB can look good after soldering but still have reliability problems. Cosmetic appearance alone doesn’t guarantee a reliable joint. Issues such as poor wetting, overheating, ionic contamination, or incorrect process settings can create hidden failures that may only show up later.
I wanted to start a discussion on the practical soldering tips that designers and assemblers should keep in mind.
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A few important points that often get overlooked:
- Cosmetically acceptable solder joints are not enough; the process must also produce reliable connections.
- Overheating components during touch-up can cause damage even when the solder joint looks good.
- Reliability cannot be fully determined through inspection alone. Visual inspection does not reveal every underlying reliability issue.
- Constant-temperature soldering irons can still damage components if heat is applied incorrectly. Heat sinking can help protect heat-sensitive components.
- What is often called cold solder can be a wetting issue. IPC-A-610G describes cold solder as a poor-wetting connection with a grayish, porous appearance.
Other practical considerations include:
- Avoid outdated terminology such as acid flux. Using accurate terminology helps avoid confusion during process discussions.
- Pinholes or small voids are not necessarily process defects. Depending on the IPC class and whether base metal is exposed, they may be acceptable. They can occur naturally due to minor outgassing during solidification or volumetric shrinkage as the solder cools.
- Reliable soldering requires meeting all the fundamental requirements. Compensating for one incorrect process condition can create additional problems.
The goal is not just to produce solder joints that look good under magnification, but to produce connections that remain reliable over the product’s lifetime.
Of course, the best soldering approach depends on the components, surface finish, and assembly process, so it’s important to align with your assembly partner early.
For a concise set of practical soldering tips covering reliability, inspection, heat management, and common misconceptions, check out our article: 8 Soldering Tips To Watch Out For.
