Professional PCB Multilayer Board Pressing Process Description (1)

Professional PCB Multilayer Board Pressing Process Description

1. Autoclave
It is a container filled with high-temperature saturated water vapor and high pressure can be applied. The laminated substrate 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 by the industry. In addition, in the multi-layer 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 laminating method of early multi-layer 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 until the end of 1984 that the output of MLB greatly increased, and it was changed to the current copper skin type large or mass pressing method (Mss Lam). This early MLB pressing method using a single-sided copper thin substrate is called Cap Lamination.

3. Crease
In multi-layer 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.

4. Dent
It refers to the gentle and uniform sag on the copper surface, which may be caused by the partial 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.

5. Caul Plate
When multi-layer boards are pressed together, in each opening of the press, many “books” of bulk materials (such as 8 to 10 sets) of the board to be pressed are often stacked, 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. At present, AISI 430 or AISI 630 are commonly used.

6. Foil Lamination
Refers to the mass-produced multi-layer board, the outer layer of copper foil and film is directly pressed with the inner skin, which becomes the multi-row board large-scale pressing method (Mass Lam) of the multi-layer board, to replace the early tradition of single-sided thin substrates suppress legally.

7. Kraft Paper
When multi-layer boards or substrate boards are laminated, kraft paper is mostly used as a heat transfer buffer. It is placed between the hot Platern of the laminator and the steel plate to ease the temperature rise curve closest to the bulk material. Between multiple substrates or multilayer boards to be pressed. Try to reduce the temperature difference of each layer of the board as much as possible. Generally, the commonly used specification is 90 to 150 pounds. After the high temperature and high pressure, the fiber in the paper has been crushed and no longer has toughness and is difficult to function. Therefore, it must be replaced with a new one. This kind of kraft paper is a mixture of pinewood 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.

8. Kiss Pressure, low pressure
When the multi-layer board is pressed, when the plates in each opening are placed and positioned, they will start to heat and be lifted up by the lowermost layer of heat. The powerful hydraulic jack (Ram) is lifted upwards to compress the openings ( Bulk materials in Opening) are bonded together. 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 flow of the glue. This initial lower pressure (15-50 PSI) is called “kiss pressure”. However, when the resin in the bulk materials of each film is heated to soften and gel, and is about to harden, it is necessary to increase to the full pressure (300-500 PSI), so that the bulk materials can be tightly combined to form a strong multi-layer board.

9. Lay Up
Before pressing the multilayer board or substrate, it is necessary to align, or register up and down various bulk materials such as the inner layer board, film and copper sheet with the steel plate, kraft paper padding, etc., for convenience, 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 the multi-layer board, not only this kind of “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 ) in construction. Even “automated” overlapping methods are needed to reduce human errors. In order to save workshops and shared equipment, most factories generally combine “lay up” and “folding boards” into a comprehensive processing unit, so automation engineering is quite complicated.