What a Tangled (Soldering) Web We Weave!


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Soldering remains one of the most critical processes in the PCB assembly industry as it "makes or breaks" a finished product—figuratively and literally (for one, cracked solder joints on a circuit board were said to be the main contributor to the fatal crash of Indonesia AirAsia flight QZ8501 on December 28, 2014). The cost of failure is just too high.

Therefore, it is of the utmost importance that the soldering quality should be perfect. But the thing is, soldering is just too complex a process, and further complicating the situation, the process, materials and technologies vary between our industry’s market segments. There are just a lot of factors to consider before you put your boards into the reflow and let them run. Soldering for different end-markets or applications—military/aerospace electronics, automotive electronics, medical electronics, or consumer electronics—have their own set of requirements. The military/aerospace sector, for one, still uses leaded solder, while the rest have moved on to lead-free.

According to our recent survey on soldering, there are myriad factors to consider based on the different end markets. There’s the increased inspection when it comes to high-reliability applications; thermal considerations; solder paste, bar and flux considerations; coating selection; equipment; and the cleaning process, to name a few.

And then there’s the issue of solder paste selection or qualification. In our soldering survey, respondents highlighted challenges such as rheology of the paste, consistency, type of solder to use, cleanliness—or ensuring their current cleaning processes can remove the fluxes, printability, and even the “irrational customer preferences.” There’s a paralysis of choice as there are too many choices and fine differences to account for when selecting a solder paste.

When it comes to their greatest challenges, respondents to the survey highlighted thermal issues, solder selection, reflow profiles, voiding, component size variations, rework, and inspection, among others.

Still, there seems to be a misconception when it comes to no-clean flux, as about 23% of the respondents in our survey believe that using no-clean flux will result in “bright and shiny solder joints” and will save them from cleaning costs as there should be no residues left on the board. Of course, with no-clean fluxes available for quite a long time now, a third of respondents know that using it doesn’t necessarily mean clean boards, but they said they still clean their boards especially when they are used in aerospace applications.

The soldering process offers issues and challenges so wide and complex that it would require a book to discuss in detail. Even then, new market trends will continue to drive the evolution in the soldering process and developments in new solder technologies.

To read the full version of this article, which appeared in the April 2017 issue of SMT Magazine, click here.

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