1. Minimize temperature-induced stress on the circuit board
Since “temperature” is the primary source of stress on the circuit board, reducing the reflow oven’s temperature or slowing the heating and cooling rates during production can significantly decrease the likelihood of bending and warping. This approach can substantially mitigate such deformations; however, it may introduce other risks, such as solder short circuits.
2. Utilize high Tg PCBs
1. Tg is the glass transition temperature, marking the point where a material transitions from a glassy state to a rubbery state. A lower Tg value means the circuit board softens more quickly in the reflow oven, leading to increased deformation. Higher Tg boards enhance resistance to stress and deformation but come at a higher cost.
2. Increase the thickness of the board. To achieve lighter and thinner designs, many electronic products utilize thicknesses of 1.0mm, 0.8mm, or even 0.6mm, which are crucial for preventing deformation during reflow. However, for applications where thinness isn’t critical, opting for a thickness of 1.6mm is advisable, significantly reducing bending and deformation risks.
3. Reduce the size of the circuit board and minimize the number of panels. Most reflow ovens drive circuit boards forward using chains, and larger designs can deform due to their weight. It’s best to position the long side of the board along the edge on the chain to minimize sagging. Consequently, reducing the number of panels is also beneficial; after the reflow process, align the narrow side perpendicular to the furnace direction to achieve minimal depression.
4. Use oven tray fixtures. If previous methods are impractical, utilizing an oven tray can help minimize deformation. The tray supports the board against thermal expansion and contraction, maintaining its size once it cools below the Tg value. If a single-layer tray is insufficient, adding a layer on both upper and lower pallets can further clamp the board, significantly reducing deformation in the reflow oven, though these trays can be expensive and require manual handling.
5. Use a router instead of V-Cut. V-Cutting can compromise the structural integrity of the material between sections, so it’s advisable to avoid V-Cut techniques or minimize the cut depth.
