Causes and solutions for foaming of multilayer circuit boards
Multilayer circuit board foaming reasons
(1) Improper suppression causes air, moisture and contaminants to be hidden;
(2) In the pressing process, due to insufficient heat, the cycle is too short, the quality of the prepreg is poor, and the function of the press is not correct, so that the degree of curing is problematic;
(3) The surface of the inner layer is blackened or the surface is contaminated when it is blackened;
(4) the inner layer or prepreg is contaminated;
(5) insufficient glue flow;
(6) Excessive flow of glue - almost all of the glue contained in the prepreg is extruded outside the board;
(7) Under the requirement of no function, the inner layer plate minimizes the appearance of large copper surface (because the bonding force of the resin to the copper surface is far lower than the bonding force of the resin and the resin);
(8) When vacuum pressing is used, the pressure is insufficient, which impairs the flow rate and adhesion of the glue (the residual stress of the multilayer board pressed by the low pressure is also less).
Multilayer circuit board foaming solution
(1) The inner layer board is baked and kept dry before being laminated.
Strictly control the process procedures before and after pressing to ensure that the process environment and process parameters meet the technical requirements.
(2) Check the Tg of the pressed multilayer board, or check the temperature record of the pressing process.
The pressed semi-finished product was further baked at 140 ° C for 2-6 hours, and the curing treatment was continued.
(3) Strictly control the process parameters of the oxidation tank and the cleaning tank of the blackening production line and strengthen the appearance quality of the board surface.
Try double-sided copper foil (DTFoil).
(4) The work area and storage area need to be strengthened for clean management.
Reduce the frequency of freehand handling and continuous take-up.
Various loose materials in the lamination work need to be covered to prevent contamination.
When the tool pin must be subjected to a surface treatment for lubrication and off-loading, it should be separated from the lamination work area and cannot be carried out in the lamination work area.
(5) Appropriately increase the pressure strength of the pressing.
Appropriately slow down the heating rate to increase the glue time, or add more kraft paper to ease the heating curve.
Replace the prepreg with a higher amount of glue or a longer gel time.
Check that the surface of the steel plate is flat and free of defects.
Check if the length of the locating pin is too long, causing the heating plate not to be tight and the heat transfer is insufficient.
Check that the vacuum system of the vacuum multi-layer laminator is good.
(6) Adjust or reduce the pressure used appropriately.
The inner layer before pressing needs to be baked and dehumidified, because the moisture will increase and accelerate the amount of glue.
Use a prepreg with a lower flow or a shorter gel time.
(7) Try to etch away the useless copper surface.
(8) Appropriately increase the pressure strength used for vacuum pressing until five passes of the floating solder test (each time is 288 ° C, 10 seconds).