3.3 compression study
The effect of the pressing on the deformation is very important. Through the reasonable parameter setting, the press selection and the stacking way can effectively reduce the stress generation. For the general structure of the symmetrical plate, the general need to pay attention to the pressure when the symmetrical stack, and symmetrically placed tool board, cushioning materials and other auxiliary tools. At the same time, the choice of hot and cold presses is also helpful in reducing the thermal stress, because the hot and cold split press at high temperature (GT temperature above) the plate to the cold press, the material above the Tg point pressure and Rapid cooling will lead to the rapid release of thermal stress deformation, and hot and cold integrated press can be hot and cold section to cool, to avoid the plate at high temperature pressure.
At the same time, for the special needs of customers, there will inevitably be some material or structural asymmetry of the plate, then the previous analysis of the CTE due to the different deformation will be very obvious, for this problem we can try to use asymmetric The principle of the asymmetric placement of the buffer material to achieve the PCB board double-sided heating rate is not the same, thus affecting the different CTE core cypress trees in the heating and cooling stages of the ups and downs to solve the problem of inconsistent deformation. Table 4 is the result of the test on the asymmetry plate of a certain structure.
Through the asymmetric stacking method, as well as after the increase in post-curing curing process, and in the ship before the level of operation, the board eventually meet the requirements of customers 2.0mm.
Figure 2 different CTE core plate during the deformation process
3.4 Other production processes
PCB production process, in addition to pressure and there are resistance to welding, characterization and hot air leveling several high-temperature treatment process, which resistance welding, character after the maximum temperature of 150 ℃ in the above mentioned temperature in the ordinary Tg material Tg point above the material at this time for the high elastic state, easy to deformation under the external force, so to avoid the drying plate when the stack to prevent the lower plate was bent, and to ensure that the direction of the board and the direction of blowing parallel to the direction of blowing. In the hot air leveling process will have to ensure that the board out of the tin furnace flat cooling more than 30s, to avoid the high temperature after the cold water wash lead to quenching deformation.
In addition to the production process, the PCB board in the storage of the station also has a certain impact on the deformation, in some manufacturers due to more production, the venue for small reasons, will be stacked together stacked storage, which will lead to board Pieces due to external deformation, because the PCB board also has a certain plastic, so these deformation in the back of the leveling process will not be 100% recovery.
3.5 pre-shipment level
Most PCB manufacturers in the shipment before there will be leveling process, it is because in the processing process will inevitably produce heat or mechanical force generated by the deformation of the plate, before the ship through the mechanical leveling or thermal correction level can Get an effective improvement. Resistance to the surface of the coating and the heat resistance of the surface coating, the general drying temperature of 140 ℃ ~ 150 ℃ below, just over the temperature of ordinary materials Tg, which is a common plate leveling is very good, and for high Tg materials The leveling effect is not so obvious, so the individual plate Alice serious high Tg plate can be appropriate to improve the drying temperature, but the main ink and coating quality. At the same time, the weight of the baking sheet, the increase with the furnace cooldown time also has some improvement on the deformation effect, Table 5 for different pressure and furnace cooling time on the plate leveling effect test results, from which you can see the increase in pressure And to extend the furnace cooling time on the deformation of the leveling have a significant effect.