Professional PCB Multilayer Board Pressing Process Description
19. Sequential Lamination
It means that the special pressing process of the multilayer PCB board is not completed at one time, but is divided into several times and gradually pressed to increase its level, and the blind hole or buried hole method is used to achieve the “interconnection” features. This method can save all through holes that must be drilled on the surface of the board. This can free up more board space to increase the number of wiring and mounting SMDs, but the manufacturing process has been prolonged.
In the circuit board industry, this word has always been commonly used in the expression of the Resin Starvation problem in multilayer board pressing. Refers to poor resin flow or improper combination of pressing conditions, resulting in partial lack of glue in the board after the completion of the multilayer board.
Refers to the multi-layer board, which often causes a little sliding displacement of the inner board surface circuit during the pressing, which is called Swimming. This has a lot to do with the “Gel Time” of the film used. At present, the industry has tended to use shorter gel time, so the problem has been reduced a lot.
In order to prevent the trouble of glue overflow in the early lamination of multi-layer boards, a heat-resistant film (such as Tedlar) was added to the copper foil or thin substrate that has been stacked with loose materials to facilitate demoulding or separation after pressing. However, when the film used for the outer layer board is thinner and the copper foil is only 0.5 oz, the circuit pattern of the inner layer board may be transferred to the release paper under high pressure. When this release paper is reused on a batch of boards, it is likely that the original pattern will be embossed on the copper surface of the new board. This phenomenon is called Telegraphing.
23. Vacuum Lamination
This term often appears in the pressing of multilayer boards and the bonding of dry films in the circuit board industry. The vacuum pressing of multi-layer boards is divided into vacuum frame type, which is the “pumping method” that matches the original hydraulic press, and the vacuum chamber type (Autoclave), which uses high temperature and high pressure carbon dioxide “air pressure method” for pressing. The former hydraulic vacuum press has simple equipment, low price and convenient operation, so it occupies more than 90% of the market. For the latter, the equipment and operation are very complicated, and the volume is also large, and the cost of the required consumables is relatively expensive, so there are not many adopters.
Often refers to a large amount of glue flowing during pressing. Cause the outer layer strength and hardness to be slightly worse, such as wrinkles or creases that often occur in 0.5oz copper foil, called Wrinkle. This term is also used in other fields.
25. Zero Centering
When stacking and registering the bulk materials of the multilayer board, a special tool notch is used. The two short sides of these rectangular notches are arc-shaped, and the width of the two long straight sides can match the insertion of the aligning pin. (Called Flated Round Pin). This kind of notches can be distributed in the center of the four sides of the bulk material, and one of the long side notches is deliberately offset to prevent foolishness. In this way, the plates can expand outwards respectively at high temperatures. It can be retracted freely when cooled, but the central plate area can be stable and unchanging, avoiding the tensile stress between the fixing hole and the pin, which is called center-invariant superimposition. Practical units are the most popular among American Multiline products.
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