The change of substrate size in PCB Manufacturing process

The change of substrate size in PCB Manufacturing process


Reasons:

(1) The difference of longitude and weft direction results in the change of substrate size, and the shearing stress remains in the substrate because of not paying attention to the fiber direction when shearing, once released, the shrinkage of the substrate size is directly affected.


(2) The copper foil on the surface of the substrate is etched to restrict the change of the substrate, and the size change occurs when the stress is eliminated.


(3) When brushing board, the pressure is too large, which results in the deformation of the substrate.


(4) The resin in the substrate is not cured completely, resulting in the change of the size.


(5) The storage conditions of multilayer plate before lamination are poor, which makes the thin substrate or semi-solidified sheet hygroscopic, resulting in poor dimensional stability.


(6) When multilayer board is pressed, excessive flow glue causes deformation of glass cloth.


Solutions:

(1) Determine the variation law of longitude and weft direction to compensate on the film according to the shrinkage rate (this work is done before the light drawing. At the same time, when shearing, it is processed in the fiber direction, Or according to the manufacturer on the substrate provided by the character mark processing (usually the vertical direction of the character is the longitudinal direction of the substrate.


(2) When designing the circuit, the whole board should be distributed evenly. If it is not possible, the transition section must be left in the space. This is due to the difference of warp and weft density in the glass cloth structure. Leads to the difference of longitudinal and weft strength of board.


(3) The test brush should be used to make the process parameters in the best condition, and then the rigid board should be carried out. For the thin substrate, the chemical cleaning process or electrolysis process should be used when cleaning the thin substrate.


(4) The method of baking is adopted, especially before drilling, the temperature is 120 ℃ for 4 hours, so as to ensure resin curing and reduce the deformation of substrate size due to the influence of cold and heat.


(5) The oxidized substrate in the inner layer must be baked to remove moisture, and the treated substrate should be stored in a vacuum dryer so as not to absorb moisture again.


(6) It is necessary to test the process pressure, adjust the process parameters and then press it. At the same time, according to the characteristics of the semi-solidified sheet, we can select the appropriate amount of flow glue.