Professional PCB Multilayer Board Pressing Process Description (2)

10. Mass Lamination
This is a new construction method in which the multi-layer PCB board pressing process abandons “aligning pins” and adopts multiple rows of boards on the same surface. Since 1986, when the demand for four- and six-layer boards has increased, the pressing method of multi-layer boards has been greatly changed. In the early days, there was only one shipping board on a processing board to be pressed. This one-to-one arrangement has been broken by the new method. It can be changed to one-to-two, one-to-four, or even more according to its size. The row boards are pressed together. The second new method is to cancel the registration pins of various bulk materials (such as inner sheet, film, outer single-sided sheet, etc.), instead use copper foil for the outer layer, and pre-make “targets” on the inner layer board. To “sweep” out the target after pressing, and then drill the tool hole from its center, then it can be set on the drilling machine for drilling. As for the six-layer board or the eight-layer board, the inner layers and the sandwich film can be riveted first with rivets, and then pressed together at high temperature. This simplifies, fast and enlarges the area of ​​pressing, and can also increase the number of “stacks” (High) and the number of openings (Opening) according to the substrate-style approach, which can reduce labor and double the output, and even automate. This new concept of pressing plates is called “mass pressing plates” or “large pressing plates”. In recent years, many professional contract manufacturing industries have emerged in China.

11. Platen
It is a movable platform that can be lifted and lowered in the laminating machine required for multi-layer board pressing or substrate manufacturing. This kind of thick hollow metal table is mainly to provide pressure and heat source to the plate, so it must be flat and parallel at high temperature. Usually each platen is pre-buried with steam pipes, hot oil pipes or resistance heating elements, and the outer edges of the surroundings must also be filled with insulating materials to reduce heat loss, and a temperature sensing device is provided to enable temperature control.

12. Press Plate
It refers to the substrate or multi-layer board used to separate each set of loose books (referring to a book composed of copper plate, film and inner layer board) when the substrate or multi-layer board is pressed. This kind of high-hardness steel plate is mostly AISI 630 (hardness up to 420 VPN) or AISI 440C (600 VPN) alloy steel. Its surface is not only extremely hard and flat, but also after careful polishing to a mirror-like surface, it can press out the flattest substrate or circuit board. Therefore, it is also called Mirror Plate and Carrier Plate. This kind of steel plate has strict requirements. There should be no scratches, dents or attachments on the surface, the thickness should be uniform, the hardness should be sufficient, and it should be able to withstand the corrosion of chemicals generated during high temperature pressing. After each pressing is completed and the board is removed, it must be able to withstand strong mechanical brushing, so the price of this kind of steel plate is very expensive.

13. Print Through And Excessively Squeezed
The pressure intensity (PSI) used when the multilayer board is laminated is too large, so that a lot of resin is extruded out of the board, causing the copper skin to be directly pressed on the glass cloth, and even the glass cloth is also flattened and deformed, resulting in insufficient board thickness, poor dimensional stability, and the lack of internal circuits such as compression and aliasing. In severe cases, the line foundation is often in direct contact with the glass fiber cloth, burying the “anode glass fiber filament” leakage concerns (Conductive Anodic Filament; CAF). The fundamental solution is the principle of scaled flow. The large-area pressing should use large pressure strength, and the small plate surface should use small pressure strength; that is, use 1.16PSI/in2 or 1.16Lb/in4 as the benchmark. Calculate the pressure intensity (Pressure) and total pressure (Force) of the on-site operation.

14. Relamination (Re-Lam) Multi-Layer Board Pressing
The thin substrate used for the inner layer is made by the substrate supplier using the film and the copper sheet to be pressed together. Laminates are often called “re-compression” or Re-Lam for short in some occasions. In fact, this is just a kind of “sniff” term for multi-layer board pressing, and it has no deeper meaning.

15. Resin Recession
Refers to the resin in the B-stage film or thin substrate of the multilayer board (the former is even worse), which may not be completely hardened after pressing (that is, the degree of polymerization is insufficient), and the through-holes are after the tin column is filled with tin. When performing a section inspection, it was found that some under-polymerized resin behind the copper hole wall would shrink from the copper wall and appear voids, which is called “resin sinking”. This kind of shortcoming should be classified as the overall problem of the manufacturing process or the board, and the degree is more serious than that of the scratch on the surface of the board, and the cause needs to be investigated carefully.

16. Scaled Flow Test
It is a method for detecting the amount of glue flowing in the film when multi-layer boards are laminated. It is a test method for the “Resin Flow” exhibited by resin under high temperature and high pressure.

17. Temperature Profile
In the circuit board industry, the pressing process, or downstream assembly of infrared or hot air welding (Reflow) and other processes, all need to find the best “temperature curve” composed of temperature (vertical axis) and time (horizontal axis). In order to improve the yield of solderability in mass production.

18. Separator Plate
When the substrate board or multi-layer board is pressed, the hard stainless steel plate (such as 410, 420, etc.) in each opening (Opening, Daylight) of the press is used to separate the books. In order to prevent sticking, the surface is specially treated to be very flat and bright, so it is also called Mirror Plate.