Microwave Tech - Overview of multilayer PCB board pressing process

1. Autoclave pressure cooker
   
   It is a container filled with high-temperature saturated water vapor and high pressure can be applied. The laminated substrate (Laminates) sample can be placed in it for a period of time to force moisture into the board, and then take out the sample again. Place it on the surface of high-temperature molten tin and measure its "delamination resistance" characteristics. This word is also synonymous with Pressure Cooker, which is commonly used in the industry. In addition, in the multi-layer PCB board pressing process, there is a "cabin press method" with high temperature and high pressure carbon dioxide, which is also similar to this type of Autoclave Press.
   
   2. Cap Lamination method
   It refers to the traditional lamination method of early multi-layer PCB boards. At that time, the "outer layer" of MLB was mostly laminated and laminated with a thin substrate of single-sided copper skin. It was not used until the production of MLB increased greatly at the end of 1984. The current copper-skin type large-scale or mass pressing method (Mss Lam). This early MLB pressing method using a single-sided copper thin substrate is called Cap Lamination.
   
   3. Caul Plate partition
   When multi-layer PCB boards are pressed, a lot of bulk materials (such as 8~10 sets) of the board to be pressed are often stacked between each opening of the press (Opening), and each set of "bulk materials" (Book) must be separated by a flat, smooth and hard stainless steel plate. The mirror stainless steel plate used for this separation is called Caul Plate or Separate Plate. Currently, AISI 430 or AISI 630 are commonly used.
   
   4. Crease wrinkles
   In multi-layer PCB board pressing, it often refers to the wrinkles that occur when the copper skin is improperly handled. Such shortcomings are more likely to occur when thin copper skins below 0.5 oz are laminated in multiple layers.
   
   5. Dent depression
   It refers to the gentle and uniform sag on the copper surface, which may be caused by the local point-like protrusion of the steel plate used for pressing. If it shows a neat drop of the faulty edge, it is called Dish Down. If these shortcomings are unfortunately left on the line after copper corrosion, the impedance of the high-speed transmission signal will be unstable and noise will appear. Therefore, such a defect should be avoided as much as possible on the copper surface of the substrate.

   
   6. Foil Lamination method
   Refers to the mass-produced multi-layer PCB board, the outer layer of copper foil and film is directly pressed with the inner layer, which becomes the mass lam of the multi-layer PCB board to replace the early single-sided thin substrate The traditional suppression is legal.
   

7. Kiss Pressure, low pressure
When the multi-layer PCB board is pressed, when the plates in each opening are placed and positioned, they will start to heat up and be lifted up by the hottest layer of the bottom layer, and lift up with a powerful hydraulic jack (Ram) to compress the openings (Opening) the bulk materials are bonded. At this time, the combined film (Prepreg) begins to gradually soften or even flow, so the pressure used for the top extrusion can not be too large to avoid slippage of the sheet or excessive outflow of the glue. This lower pressure (15-50 PSI) initially used is called "kiss pressure". However, when the resin in each bulk material is heated to soften and gel, and is about to harden, it needs to be increased to the full pressure (300-500 PSI), so that the bulk materials can be tightly combined to form a strong multilayer PCB board.

8. Kraft Paper
When multi-layer PCB boards or substrate boards are laminated (laminated), kraft paper is mostly used as a heat transfer buffer. It is placed between the hot plate (Platern) of the laminator and the steel plate to ease the heating curve closest to the bulk material. Between multiple substrates or multilayer PCBs to be pressed. Try to reduce the temperature difference of each layer of the board as much as possible. Generally, the commonly used specifications are 90 to 150 pounds. Because the fiber in the paper has been crushed after high temperature and high pressure, it is no longer tough and difficult to function, so it must be replaced with a new one. This kind of kraft paper is co-cooked with a mixture of pine wood and various strong alkalis. After the volatiles escape and the acid is removed, it is washed and precipitated. After it becomes pulp, it can be pressed again to become rough and cheap paper. material.

9, Lay Up stacking
Before pressing multi-layer PCB boards or substrates, various bulk materials such as inner layer boards, films and copper sheets, steel plates, kraft paper pads, etc., need to be aligned, aligned, or registered up and down to prepare Then it can be carefully fed into the pressing machine for hot pressing. This kind of preparatory work is called Lay Up. In order to improve the quality of multi-layer PCB boards, not only this "stacking" work must be carried out in a clean room with temperature and humidity control, but also for the speed and quality of mass production, generally the large-scale pressing method (Mass Lam) construction even needs to use "automated" stacking methods to reduce human errors. In order to save workshops and shared equipment, most factories generally combine "stacking" and "folding boards" into a comprehensive processing unit, so the automation engineering is quite complicated.

10. Mass Lamination (Lamination)
This is a new construction method in which 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 PCB 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 through in 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 of the 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 the pressing, and can also increase the number of "stacks" (High) and the number of openings (Opening) according to the substrate-based approach, which can reduce labor and double the output, and even automate. This new concept of pressing plate is called "large pressing plate" or "large pressing plate". In recent years, there have been many professional foundry pressing industries in China.