Special ink for assistance in manufacture of backdrill and PCB (printed circuit board) backdrilling method

Abstract

The invention provides special ink for assistance in the manufacture of a backdrill and a PCB (printed circuit board) backdrilling method. The special ink is mainly made from propylene glycol monomethyl acetate, pumice powder and water-soluble resin, wherein the propylene glycol monomethyl acetate accounts for 20-25% by mass, the pumice powder accounts for 50-60% by mass, and the water-soluble resin accounts for 20-25% by mass. The PCB backdrilling method comprises the steps of 1) stacking a plurality of core plates in order to form a substrate, drilling the substrate to obtain via holes, andplating; 2) providing the special ink to plug the via holes, baking, and grinding the end faces of the via holes; 3) drilling a drill rig, and backdrilling to a preset depth on one side of the via holes, with coaxial alignment to the via holes; 4) subjecting the backdrilled holes to high pressure spraying via a spraying liquid so as to remove resin residue in the holes, so that the via holes are smooth. The problem that large-thickness and -diameter copper wires / fragments block the via holes is successfully solved.

Description

technical field [0001] The invention relates to a back-drilling method on a printed circuit board (PCB). Background technique [0002] At present, the precision control of back-drilling STUB in the industry is still a common technical problem. STUB means that after the circuit board is drilled and plated, the plated hole is drilled through back-drilling (the diameter of the drill hole is larger than that of the plated hole), and the plated hole is drilled to a certain depth. Finally, the length of the remaining copper from the bottom of the back-drilled hole wall to the non-drilled layer is the STUB. At present, the STUB accuracy control mainly depends on the accuracy improvement of the drilling equipment and the uniformity control of the plate thickness. The current back-drilling technology is actually The depth-controlled drilling technology adopts the construction of the zero height of the drilling hole, and then sets a certain drilling depth value to complete the back-dr...

AI Technical Summary

Problems solved by technology

[0002] At present, the precision control of back-drilling STUB in the industry is still a common technical problem. STUB means that after the circuit board is drilled and plated, the plated hole is drilled through back-drilling (the diameter of the drill hole is larger than that of the plated hole), and the plated hole is drilled to a certain depth. Finally, the length of the remaining copper from the bottom of the back-drilled hole wall to the non-drilled layer is the STUB. At present, the STUB accuracy control mainly depends on the accuracy improvement of the drilling equipment and the uniformity control of the plate thickness. The current back-drilling technology is actually The depth-controlled drilling technology adopts the construction of the zero height of the drilling hole, and then sets a certain drilling depth value to complete the back-drilling. When the plate thickness fluctuates, it is impossible to achieve accurate back-drilling copper retention control. In addition, when back-drilling, At present, the problem of back-drilling copper wire / copper broken plug holes with high thickness-to-diameter ratio is a problem that is difficult to overcome in the industry, such as figure 1 As shown, a substrate is formed by pressing several core boards. The substrate is mainly filled with resin and glass fiber. The substrate contains inner layer copper 101. There are electroplating holes 102 on the substrate. The substrate is plated on the surface of the substrate and the wall of the electroplating hole 102. Plating layer 103 is formed on the electroplating hole 102. When back drilling the electroplating hole 102, because of the extrusion when the drill bit falls, when the dust and chip removal in the electroplating hole 102 is not sufficient, the copper wire and copper fragments 104 falling on the electroplating hole 102 hole wall will be damaged. It is squeezed into the remaining hole section after the electroplating hole is drilled, causing the remaining hole section of the electroplating hole to be plugged with copper wire and copper broken 104, which is more obvious in the case of high plate thickness and small aperture; at the same time, the existing back drill Technology cannot precisely control the distance from back drilling depth to target layer 105

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