In the electronic devices we use daily—such as remote controls, smartphones, refrigerators, TVs, air conditioners, and computers—there is a crucial component called the Printed Circuit Board (PCB). The name comes from the way its electrical circuits are formed, similar to early book printing. Some also refer to it as a Printed Wire Board (PWB).
A user asked: “During the SMT process, PCBs often warp or bow after going through reflow high temperature. In severe cases, this can lead to defects like insufficient solder joints or tombstoning. How can we prevent and solve this issue?”
To be honest, the reasons behind PCB warping and bowing may vary, but in the end, it all comes down to one key factor—when the stress applied to the PCB exceeds the material’s ability to withstand it. If the PCB experiences uneven stress or different areas of the board have varying resistance to stress, warping and bowing will occur.
Recently, our company started a new project, and the R&D team has been pushing PCB layout requirements to the extreme. As PCBs size get smaller, the solder mask (S/M) design must also shrink accordingly. However, our current PCB manufacturers struggle to meet these tighter tolerances, and those who can do it demand a price increase. The moment extra cost is mentioned, everyone hesitates and sticks with the existing PCB suppliers, resulting in solder mask misalignment that extends beyond the pads.
In the early days, when electronic component design and manufacturing were still in their infancy, burn-in (B/I) was widely used to screen out defective products. This process helped eliminate early failures before products reached customers, reducing the risk of complaints.
Statistical data shows that electronic products typically follow a bathtub curve in terms of lifespan. This means that failure rates are higher during the initial (infant mortality period or child mortality period) and end-of-life (wear-out period) phases, but once a product passes the early stage, its failure rate drops significantly and stabilizes close to zero (useful life period or normal period)—just like the shape of a bathtub.
Glass Transition Temperature (Tg) is one of the most important properties of all plastic and epoxy resin materials. In fact, the Tg value is also an indicator of the quality of the fiberglass fabric used in PCB manufacturing. However, compared to Heat Deflection Temperature (HDT), Tg is generally considered less critical. Tg typically refers to the temperature at which the molecular chains of a plastic begin to undergo large-scale motion at the microscopic level.
