Discussion on PCB Inner Layer Plug Hole Manufacturing Technology (3)

Two-stage hot-baking hardening type plug ink, its hardening process can be divided into two stages, the first stage of hardening is pre-backing, and the degree of ink hardening after pre-baking is usually 4-5H. Grinding can also reduce the grinding cost. After the grinding is completed, the second stage of hardening is performed, which is called post-curing. After the second stage of baking, the ink can harden up to 8-9H. Although the two-stage baking takes more baking time, the overall efficiency (especially the plugging quality and brushing benefit) is better than that of the one-stage hot-baking hardening plugging ink. The Noda plugging process is the most famous user of UV exposure heat-bake-hardening plugging ink. The process is similar to the two-stage heat-baking-hardening plugging ink, except that the first-stage curing Pre-Curing uses the low-temperature liquid exposure machine successfully developed by Noda Company is exposed and hardened in the low-temperature liquid environment. The hardness after hardening is about 2-3H, and then the brushing and post-baking operations are performed. The company’s exclusive technology and the limited information disclosed cannot be described here.

At present, most of the inner layer plugging inks on the market has been changed to solvent-free formulations regardless of the hardening type. The solvent will be volatilized by heat during the baking process, but if the plughole diameter is when the aspect ratio is high, it will be relatively difficult for the solvent to be completely discharged, and some of the solvents will remain in the hole, and the residual solvent will expand again in the process of heating again. At this time, it is possible to form cracks in the ink. Especially when the high temperature and short time baking method is combined with the high Aspect Ratio pore size, it is easy to produce skinning over effect that the ink at the orifice has hardened but the ink inside the pore size is not completely hardened, so it is easier for the solvent to remain in the hole. Causes poor plugging; low temperature and long-term baking can avoid the above situation and help the discharge of volatile components in the ink. 100% solid content and solvent-free plugging ink can reduce the expansion and hardening of residual solvent. The shrinkage of the post ink is minimized.

5. Grinding Methods

In order to ensure the grinding quality of the inner plug hole and avoid abnormal grinding quality caused by improper grinding equipment and grinding conditions, it is necessary to focus on the hole depression, hole angle damage, sheet expansion and shrinkage, grinding roughness, grinding amount, various characteristics such as grinding cost, sheet capacity and grinding wheel matching are required and strictly controlled to improve the overall process yield. The equipment commonly used in the inner plug hole grinding process includes:

(1) Belt Sander.
(2) Automatic pressure regulating grinder.

The grinding wheels used in the automatic pressure regulating type grinding machine include ceramic grinding wheels and non-woven grinding wheels. The grinding wheel has the better cutting ability, and the surface of the orifice will not leave dents after grinding, but its disadvantages are expensive and short service life. Non-woven grinding wheels also have excellent cutting ability, but due to their structural factors, they are more likely to leave hole depressions after grinding. If you consider the cost alone, the price is much lower than that of ceramic grinding wheels. Manufacturers can choose according to individual plugging characteristics. Choose the grinding wheel combination that is most suitable for the actual working situation. In terms of the expansion and shrinkage control of the plate, after testing with four-axis grinding. The inner layer plate is rotated 90° and then subjected to post-four-axis grinding to obtain the best grinding roughness and expansion and shrinkage control. The damage to the orifice can also be distributed bears and avoid concentration in a single direction.

6. Conclusions

At this stage, the inner layer plugging process has various suppliers with different attributes to provide options in terms of equipment, raw materials and grinding methods. The industry can find the most suitable equipment, materials and optimized production conditions according to actual needs. Carry out the inner layer plugging operation.