reason:
(1) the difference between longitude and latitude causes the change of substrate size; Due to the failure to pay attention to the fiber direction during shearing, the shear stress remains in the substrate. Once released, it will directly affect the shrinkage of the substrate size.
(2) the copper foil on the surface of the substrate is etched, which limits the change of the substrate and produces dimensional change when the stress is eliminated.
(3) when brushing the plate, the pressure is too large, resulting in compressive and tensile stress and substrate deformation.
(4) the resin in the substrate is not fully cured, resulting in size change.
(5) in particular, the multilayer board is stored under poor conditions before lamination, which makes the thin substrate or semi cured sheet hygroscopic, resulting in poor dimensional stability.
(6) when the multilayer board is pressed, excessive glue flow causes the deformation of the glass cloth.
resolvent:
(1) determine the change law of longitude and latitude direction and compensate on the negative film according to the shrinkage (this work shall be carried out before photo drawing). At the same time, it is processed according to the fiber direction or the character mark provided by the manufacturer on the substrate (generally, the vertical direction of the character is the longitudinal direction of the substrate).
(2) when designing the circuit, try to make the whole board evenly distributed. If it is impossible, the transition section must be left in the space (mainly without affecting the circuit position). This is due to the difference of warp and weft yarn density in the glass cloth structure, which leads to the difference of warp and weft strength of the plate.
⑶ trial brushing shall be adopted to make the process parameters in the best state, and then the rigid plate shall be painted. For thin base materials, chemical cleaning process or electrolytic process shall be adopted during cleaning.
(4) adopt baking method to solve the problem. In particular, bake before drilling at 120 ℃ for 4 hours to ensure resin curing and reduce the deformation of substrate size due to the influence of cold and heat.
(5) the substrate with oxidized inner layer must be baked to remove moisture. The treated substrate shall be stored in the vacuum drying oven to avoid moisture absorption again.
(6) it is necessary to conduct process pressure test, adjust process parameters, and then press. At the same time, the appropriate glue flow amount can be selected according to the characteristics of the semi cured sheet.