The stability ofmultilayer PCB material standard is the primary factor that affects thepositioning accuracy of inner layer. It is also necessary to consider theinfluence of thermal expansion coefficient of substrate and copper foil on theinner layer of multilayer PCB. From the analysis of the physical properties ofthe substrate used, the laminate contains polymers, and its primary structurewill change at a certain temperature, known as the glass transition temperatureTg. Glass transition temperature is a unique function of large number ofpolymer, next to thermal expansion coefficient, it is the most importantcharacteristic of laminates.
Electroplatedthrough holes have a lower natural expansion rate than surrounding laminates.Since the thermal expansion of the laminate is faster than that of the poreduring circuit board processing, this means that the through-hole is stretchedin the direction of the deformation of the laminate. This stress conditionoccurs in the through hole body tension stress, when the temperature rises, thetension stress will continue to increase, when the stress exceeds the throughhole coating cracking strength, the coating will crack. At the same time, thehigh thermal expansion rate of the laminate makes the stress on the inner wireand pad increase significantly, resulting in the cracking of the wire and pad,and forming a short circuit in the inner layer of multi-layer PCB.
In the process ofcircuit board processing, the selection of raw materials is also veryimportant. We should carry out in-depth analysis of the function of rawmaterials to ensure that raw materials reach certain skill requirements andbring assistance to post-processing. In the future, skills will continue todevelop, and its production method will also become more advanced with time, toensure that the standard and accuracy of the circuit board and so on meet therequirements.