PCB Tech - PCB multilayer board pressing process description

PCB manufacturer editor:

1. Autoclave pressure cooker

PCB manufacturer's editor: 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 circuit board. Then take the sample out of the plate and place it on the surface of the high-temperature molten tin to measure its "delamination resistance" characteristics. This word is also synonymous with PressureCooker, which is commonly used in the industry. In addition, in the PCB 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 AutoclavePress.

2, CapLamination method
It refers to the traditional lamination method of early PCB multi-layer boards. At that time, the "outer layer" of MLB was mostly laminated and laminated with a single-sided copper thin substrate. It was not used until the end of 1984 when the output of MLB increased greatly. The current copper-skin type large or mass pressing method (MssLam). This early MLB pressing method using a single-sided copper thin substrate is called CapLamination.

3, Crease
In the PCB 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 0.5oz are laminated in multiple layers.

4, Dent depression
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 DishDown. If these shortcomings are unfortunately left on the line after copper etching, 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, CaulPlate partition
When the PCB multilayer board is pressed, in each opening of the press (Opening), a lot of bulk materials (such as 8~10 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 CaulPlate or SeparatePlate. Currently, AISI430 or AISI630 are commonly used.

6, FoilLamination copper foil pressing method
Refers to the mass-produced PCB multi-layer board, the outer layer of copper foil and film is directly pressed with the inner layer, which becomes the multi-row board large-scale pressing method (MassLam) of the multi-layer board, to replace the early tradition of single-sided thin substrates Suppress legal.

7, KraftPaper kraft paper
When the PCB multilayer board or substrate board is pressed (laminated), kraft paper is 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 circuit board substrates or PCB multi-layer 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. 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 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.

8, KissPressure kiss pressure, low pressure
When the PCB 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, and lift up with a powerful hydraulic jack (Ram) to press each opening (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 (15-50PSI) initially used 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 (300-500PSI), so that the bulk materials can be tightly combined to form a strong multi-layer board.

9, LayUp stacking
Before pressing the PCB multilayer board or circuit board substrate, it is necessary to align, align, or register up and down various bulk materials such as the inner layer board, film and copper sheet with steel plate, kraft paper padding, etc., So that it can be carefully sent to the pressing machine for hot pressing. This kind of preparatory work is called LayUp. In order to improve the quality of the multilayer board, not only this kind of "stacking" work should 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 press method (MassLam) is used for those with less than eight layers. Construction even needs to use "automated" stacking methods to reduce human errors. In order to save workshops and shared equipment, general circuit board factories often combine "stacking" and "folding boards" into a comprehensive processing unit, so the automation engineering is quite complicated.

10, MassLamination large platen (laminated)
This is a new construction method in which the PCB multilayer 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 circuit boards has increased, the pressing method of PCB 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 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 circuit board or the eight-layer circuit board (PCB multi-layer circuit board), the inner layers and the sandwich film can be riveted first with rivets, and then pressed 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 plates is called "mass pressing plates" or "large pressing plates". In recent years, many professional contract manufacturing industries have emerged in China.

11, Platen hot plate
is a platform that can be moved up and down in the pressing machine required for PCB multilayer board pressing or substrate manufacturing. This kind of heavy 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 hot plate is pre-buried with steam pipes, hot oil pipes or resistance heating elements, and the outer edges of the surroundings also need to be filled with insulating materials to reduce heat loss, and a temperature sensing device is provided to enable temperature control.

12, PressPlate steel plate
refers to the substrate or PCB multilayer 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 PCB multilayer board is pressed. This kind of high-hardness steel plate is mostly AISI630 (hardness up to 420VPN) or AISI440C (600VPN) alloy steel. The surface is not only extremely hard and flat, but also after careful polishing to a mirror-like surface, the flattest substrate or circuit board can be pressed out. Therefore, it is also called MirrorPlate, or CarrierPlate. This kind of steel plate has strict requirements. There should be no scratches, dents or attachments on its surface, the thickness should be uniform, the hardness should be sufficient, and it should be able to withstand the corrosion of chemicals produced during high temperature pressing. After each pressing and dismantling of the board, it must be able to withstand strong mechanical brushing, so the price of this kind of steel plate is very expensive.

13, PrintThrough pressure through, excessive squeeze
The pressure strength (PSI) used when the PCB multilayer board is pressed 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 squashed and deformed, resulting in the thickness of the board. Insufficiency, poor dimensional stability, and the internal circuits of the circuit board are compressed and aliased. 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 proportional flow (ScaledFlow). Large-area pressing should use a large pressure strength, and a small plate surface should use a small pressure strength; that is, use 1.16PSI/in2 or 1.16Lb/in4 as the benchmark to calculate Pressure and total pressure (Force) of on-site operation.

14, Relamination (Re-Lam) multilayer 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. After the circuit board factory purchases the thin substrate to make the inner circuit board, the film is used to recompress the PCB. Multilayer boards are often called "re-compression" or Re-Lam for short in some occasions. In fact, this is just a kind of "sniff" term for PCB multi-layer board pressing, and it has no deeper meaning.

15, ResinRecession resin sinks, resin shrinks
Refers to the resin in the B-stage film or thin substrate of the PCB multi-layer 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 filled with tin pillars during the bleaching Later, when performing a sectioning 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 the poor craftsmanship such as the scratch on the surface of the board, and the cause needs to be investigated carefully.

16, ScaledFlowTest proportional flow test
Is a method for detecting the amount of glue flowing in the film (Prepreg) when multi-layer circuit boards are laminated. It is a test method for the "ResinFlow" (ResinFlow) exhibited by resin under high temperature and high pressure. For details, please refer to section 2.3.18 of IPC-TM-650. For the explanation of its theory and content, please refer to P.42 of the 14th issue of Circuit Board Information Magazine.

17, TemperatureProfile temperature curve
In the pressing process in the circuit board industry, or downstream assembly processes such as infrared or hot air welding (Reflow), it is necessary to find the best "temperature curve" that matches the temperature (vertical axis) and time (horizontal axis). In order to improve the yield of solderability in mass production.

18, SeparatorPlate, steel plate, mirror plate
When the substrate board or multilayer circuit 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 (Books). In order to prevent sticking, the surface is specially treated to be very flat and bright, so it is also called Mirror Plate.

19, SequentialLamination continuous compression method
It means that the special pressing process of the multilayer circuit board is not completed at one time, but is divided into several times to gradually press and increase its level, and use blind holes or buried holes to achieve the "interconnection" between some levels ( Interconnection) function. 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 dragged for a long time.

20, Starvation lacks glue
In the circuit board industry, this word has always been used to express the "lack of glue" ResinStarvation problem in PCB 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 multi-layer board.

21, Swimming line slips off
refers to the small sliding displacement of the inner layer circuit during the pressing of the multilayer circuit board, which is called Swimming. This has a lot to do with the "GelTime" (GelTime) of the film used. At present, the industry has tended to use those with a shorter gel time, so the problem has been reduced a lot.

22, Telegraphing embossed, hidden
In order to prevent the trouble of glue overflow during the early bonding of PCB 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 after pressing or The purpose of release. However, when the film used for the outer layer board is thinner and the copper foil is only 0.5oz, the circuit pattern of the inner layer board may be transferred to the release paper under high pressure. When the release paper is reused on a batch of boards, it is very likely that the original pattern will be embossed on the copper surface of the new board. This phenomenon is called Telegraphing.