Temperature is the primary source of board stress; lowering the reflow oven temperature or slowing the heating and cooling rates can significantly reduce plate bending and warpage. However, this may lead to side effects, such as solder short circuits.
2. **Using high Tg sheet**
Tg, or glass transition temperature, indicates when a material shifts from a glassy to a rubbery state. A lower Tg results in quicker softening in the reflow oven, extending the time to reach a rubbery state and increasing deformation. Employing higher Tg materials enhances stress and deformation resistance, albeit at a higher cost.
3. **Increase the thickness of the circuit board**
To achieve lighter and thinner designs, many electronic products now use boards as thin as 1.0mm, 0.8mm, or even 0.6mm. Maintaining board integrity post-reflow is challenging at these thicknesses. If lightness and thinness are not essential, a thickness of 1.6mm is recommended to significantly reduce the risk of bending and deformation.
4. Reduce PCB board size and minimize the number of panels
Since most reflow furnaces use chains to drive the circuit boards forward, larger circuit boards are prone to issues such as denting and deformation due to their weight. To mitigate this, position the long side of the circuit board along the edge of the reflow furnace’s chain. This alignment helps minimize deformation caused by the board’s weight. Additionally, reducing the number of panels follows this principle; aim to pass through the furnace using the narrow edge to further limit deformation.
5. Utilize furnace tray fixtures
If the above methods are challenging to implement, consider using a reflow carrier/template to decrease deformation. The effectiveness of a reflow carrier/template lies in its ability to stabilize the circuit board during thermal expansion and contraction. It holds the board in place until its temperature drops below the Tg value, allowing it to harden while maintaining its size. If a single-layer pallet cannot adequately reduce deformation, adding a cover to clamp the circuit board between upper and lower pallets can significantly decrease deformation during the reflow process. However, these furnace trays can be quite costly, and manual effort is required for their placement and retrieval.
6. Use routing instead of V-Cut for sub-boards
Since V-Cutting compromises the structural integrity of the board between circuit sections, it is advisable to avoid V-Cut for sub-boards or to minimize the depth of the V-Cut if it must be used.
