temperature limitations of pcb assemblers
PCBs are complex, multi-layered and require a delicate balance of temperature. While a PCB reflow oven has a fairly broad range of temperatures, pcb assemblers must be aware of the specific thermal limits of each component. This is because the different materials used in a typical pcb have varying tolerances for heat.
High temperature can cause several problems in the pcb assemblers process, including misplaced components, unsteady connections, and even structural damage to a board. The resulting issues can impact a pcb’s performance, reliability, and even safety.
During a reflow soldering process, the entire PCB is sent through a heated oven to melt and solidify the solder. This is done to ensure that the individual components are properly secured in place. The most common types of components that are added to a pcb include surface mount technology (SMT) and through-hole technology (THT).
What are the temperature limitations of pcb assemblers?
The first step in the SMT process involves applying a thin stainless steel stencil to areas of a bare circuit board. Then, the assembler applies solder paste, which consists of microscopic metal balls and a substance called flux, to the stencil. This is done by hand or with a robotic pick and place machine. After the solder paste is applied, the bare PCB is sent to a conveyor belt where it can be fed into an automated device that adds the surface-mounted components to the board.
Once the surface-mounted components are in place, the assembler can begin the THT process. The assembler will insert through-hole components by hand or with a selective soldering machine depending on the size and quantity of components. Once the thru-hole components are inserted, the assembler will use either wave soldering or reflow soldering to fix them in place.
While many factors affect a pcb’s temperature tolerance, the glass transition temperature (Tg) of the materials in a typical pcb is the most critical. This metric indicates how reliably the material stands up to heat, and it’s important for engineers to consider when designing a PCB.
Another important factor is the rate at which different materials expand in response to heat. This can be a significant issue for PCBs because it means that the dielectric and conductive layers may pull apart, creating additional heat exposure. This can also lead to oxidation, which causes the exposed dialectic material in a pcb to corrode. This can lead to a loss of transmission lines and an increase in power dissipation. As such, it’s essential for a pcb to have an optimal Tg to prevent the above-mentioned issues.