Multilayer PCB- Up To 56 Layers Manufacturing
Manufacturing multilayer PCB up to 56 layer, IPC III Standard, Multilayer Rigid PCB, Multilayer Flex PCB, Rigid-flex Board, hybrid PCB…
Multilayer PCB Stack-Up Design & its Lamination Process
Multilayer PCB or multilayer printed circuit boards are circuit boards composed of two or more conductive layers (copper layers). The copper layer is pressed together by the resin layer (prepreg). Due to the complexity of the multilayer PCB manufacturing process, low production volume, and difficulty in rework, their prices are relatively higher than a single layer and double-sided PCB.
Rayming manufacture multilayer PCB up to 56 Layer , accept pure single material or mixed-press materials :Fr4,Rogers,Polymide,metal Core .
Due to the increase in the packaging density of integrated circuits, a high concentration of interconnection lines has resulted, which necessitates the use of multilayer PCB. Unforeseen design problems such as noise, stray capacitance, and crosstalk have appeared in the printed circuit layout. Therefore, the printed circuit board design must minimize the length of signal lines and avoid parallel routes. Obviously, in the PCB single-sided board, even the double-sided board, due to the limited number of crosses circuit that can be achieved, these requirements cannot be satisfied. In the case of a large number of interconnection and crossover requirements, the PCB circuit board must be expanded to more than two layers to achieve satisfactory performance. Thus a multilayer circuit board has appeared. Therefore, the original intention of manufacturing multilayer circuit boards is to provide more freedom in selecting appropriate wiring paths for complex and noise-sensitive electronic circuits.
Multilayer PCB circuit boards have at least three conductive layers, two of which are on the outer surface, and the remaining layer is integrated into the insulating board. The electrical connection between them is usually achieved through plated through holes on the cross-section of the circuit board. Unless specified, multilayer printed circuit boards are the same as double-sided boards, generally plated through-hole boards
Advantages and disadvantages of multilayer PCB
Advantages
Small size
Multilayer PCB increase board surface area through the addition of layers, decreasing overall size. This will allow higher-capacity multilayer PCB to be used in smaller devices, while high-capacity single PCB must be installed into larger products.
High assembly density
Multi-layer PCB multiply their density through layering. This increased density allows greater functionality, improving capacity and speed despite the smaller PCB size
Lightweight
Multilayer PCB can accomplish the same amount of work as multiple single-layer board, but does so at a smaller size and with fewer connecting components, reducing weight. This is an essential consideration for smaller electronics where weight is a concern.
Multilayer PCB circuit boards have at least three conductive layers, two of which are on the outer surface, and the remaining layer is integrated into the insulating board. The electrical connection between them is usually achieved through plated through holes on the cross-section of the circuit board. Unless specified, multilayer printed circuit boards are the same as double-sided boards, generally plated through-hole boards
Disadvantages
Long manufacturing time
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High cost
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Request high-reliability testing methods
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Multilayer printed circuit is the product of electronic technology development in high speed, multi-function, large capacity, and small volume. With the continuous development of electronic technology, especially the extensive and in-depth application of large-scale and very large-scale integrated circuits, multilayer printed circuits are rapidly developing in the following directions: high density, high precision, and high layers, tiny lines and small holes, blind and buried holes, high plate thickness to aperture ratio and other technologies to meet market needs..
Why are PCB multilayer boards all even-numbered layers
- It can be manufactured in a PCB factory. The four-layer board generally uses a core with one copper foil on each sideand a three-layer board with one copper foil on one side. They must be pressed together.
- The process cost difference between the two is that the four-layer board has one more copper foil and bonding layer. The cost difference is not significant. When the PCB factory makes a quote, they are generally quoted on an even number basis. Also, 3-4 layers are commonly quoted as a grade. (For example:If you design a 5-layer board, the other party will quote at the price of a 6-layer board. That is to say, the price you design for 3 layers is the same as the price you design for 4 layers.)
- In the PCB process technology, the four-layer PCB board is better controlled than the three-layer board, mainly in terms of symmetry. The warpage of the four-layer board can be controlled below 0.7% (IPC600 standard), but the size of the three-layer board is large. At that time, the warpage will exceed this standard, which will affect the reliability of the SMT assembly and the entire product. Therefore, the designer shouldnot design the odd-numbered layer board. Even if the odd-numbered layer is necessary, it will be designed as a fake even-numbered layer. That is to design 5 layers into 6 layersand 7 layers into 8 layers.
Calculation Method of Multilayer PCB Stack-Up
B: Thickness of PP sheet
A: Thickness of inner layer
F: Thickness of outer copper foil
E: Thickness of inner copper foil
Y: Finished PCB tolerance
X: Finished board thickness
1. Calculate the upper and lower limit of pressing
Usually tin plate: upper limit -6MIL, lower limit-4MIL
Gold plate: upper limit -5MIL, lower limit -3MIL
For example, tin plate: upper limit=X+Y-6MIL lower limit=X-Y-4MIL
Calculate the median = (upper limit + lower limit)/2
≈A+the area of the second layer of copper foil%*E+the area of the third layer of copper foil%*E+B*2+F*2
The inner cutting material of the above conventional four-layer board is 0.4MM smaller than the finished board, using a single 2116 PP sheet to press. For special inner layer copper thickness and outer layer copper thickness that more than 1OZ, the copper thickness should be considered when choosing the inner layer material
Calculate the Pressing Tolerance
Upper limit = Finished board thickness + Finished on-line tolerance value-[Plating copper thickness, green oil character thickness
(Conventional 0.1MM)]-The theoretically calculated thickness after pressing
Lower limit = finished board thickness-finished product off-line tolerance value-[electroplating copper thickness, green oil character thickness
(Regular 0.1MM)]-The theoretically calculated thickness after pressing
Commonly types of PP sheets
| KB | KB | PP |
| 0.065MM | 0.07MM | 1080 |
| 0.105MM | 0.11MM | 2116 |
| 0.105MM | 0.11MM | 2116 |
Generally, do not use two PP sheets with high resin content together. If the inner layer of copper is too small, please use PP sheets with high resin content. 1080 PP sheets have the highest density and low resin content. Do not press single sheets as much as possible. Only 2 sheets of 2116 and 7630 PP sheets can be pressed into thick copper plates above 2OZ. The layer cannot be pressed by a single sheet of PP. 7628 PP sheet can be pressed by a single sheet, 2 sheets, 3 sheets, or up to 4 sheets.
Explanation of theoretical thickness calculation of multilayer PCB board after pressing
dual copper lamination thickness-inner copper thickness*(1-Remaining copper rate%)
Typical Recommendation of Multilayer Stack-Up
4 Layer PCB Stack-Up
6 Layer PCB Stack-Up
Typical Stack-Up of 8 Layer PCB
Introduction to the Multilayer PCB Lamination Process
- Lamination uses high temperature and high pressure to melt the prepreg by heat, make it flow, and turn it into a cured sheet. It is then processing one or more inner etched boards (Black Oxide Treatment) and copper foil into a multilayer board.
- This process also includes layer stack-up before lamination, drill positioning holes, and profile routing after laminated multilayer boards.
Lamination Process Flow
Multilayer PCB Manufacturing Process Steps
Remarks: For 6 layer PCB stack-up and over, two or more inner layers must be pre-positioned so that the holes and circuits of different layers have the correct alignment.
Position Methods
1) Positioning of rivet nails: press the layout of the inner layer board and prepreg with pre-drilled positioning holes
- The sequence is set on the template with rivets and then punched with a nail punch
- Rivets to position
2) Solder joint positioning: set the inner layer board and prepreg with pre-drilled positioning holes according to the layout
- The sequence is set on the template equipped with positioning pins, and then through the heating several
- A fixed point, using the prepreg to melt and solidify when heated
We are currently using solder joint positioning-RBM
Pre-punched positioning hole for the inner board, the current method we use is as follows: Punch 4 slot holes on the four sides of the board, two as a group, respectively locating in the X/Y direction, one of which is asymmetrical design. The purpose is to start to prevent a reaction.
A= 7.112±0.0254MM
B= 4.762 ±0.0254MM
| >60mil | 40mil<T<60mil | <40mil | Thickness |
| 300℃ | 300℃ | 300℃ | temperature |
| 0.8-1.0min | 0.6-0.8min | 0.3-0.5min | Time |
Quality control after RBM-potential problems
1) Interlayer offset: poor RBM positioning or poor heating point condensation, causing
Shift between layers after pressing, after drilling due to
Dislocation of the lines on each layer causes open or short.
Possible reason
- uInner layer punching deviation
- uThe expansion and contraction of the inner plate is very different
- uRBM staff deflection
- uRBM parameters do not match-the coagulation effect is not acceptable
- uRBM heating head wear-bad condensation effect
- u Lay up personnel put the board improperly, causing the heating point to fall off
2) The inner core is reversed: the order of the inner core is incorrectly placed during RBM, which affects the quality of the customer’s assembled board.
Introduction to Layer Stack-Up Process: The layout process arranges the inner core, prepreg, and copper foil with aluminum plates according to the structural requirements and reaches the required height for pressing. CEDAL layer stack-up can be divided into four main layouts according to the right picture
Introduction to Prepreg
A prepreg refers to glass fibers or other fibers impregnated with resin. After partial polymerization, the resin molecules are slightly cross-linked, which can be softened by heat. However, it cannot be completely melted.
Prepreg specifications
Main Performance characteristics of prepreg
Resin content (R/C)
Resin fluidity (R/F)
Gel time (G/T)
Volatile content (V/C)
Test - Resin Content
Resin content (RC)
1). Resin content definition: the percentage of the weight of resin in the semi-cured to the weight of the prepreg;
2). Calculation formula: RC=(TW-DW)÷TW ×100%;
RC: Resin content; TW: weight of prepreg; DW: weight of glass cloth after burning.
3) TW can be used as a control indicator when the base weight of the glass cloth is constant
- Instrument: Electronic balance, accuracy: 0.001 g
- Sample: 4 “X 4” X 4 pieces
Description of Resin Content
Resin content of prepreg (RC)
- lRC is mainly related to thethickness of the laminate.
- lThe RC is low,and the thickness of the board is thin;
- lIf the deviation of the left, middle,and right of the RC is large, the thickness uniformity of the board will be poor.
- After controlling the RC of the prepreg, the required thickness can be obtained after pressing, and the Cpk value of the thickness can be increased.
Comparison table of resin content and PP thickness
Thickness calculation after resin filling
Thickness after PP pressing
- Thickness = theoretical thickness of single PP-filling loss
- Filling loss = (1-A side copper residual copper rate) x copper foil thickness + (1-B side copper residual copper rate)
The relationship between PP film characteristic parameters and resin fluidity:
- The gel time (PG) is large,and the resin has strong fluidity;
- The fluidity (RF) is large, and the resin has strong fluidity;
- The minimum viscosity (MV) is small,and the resin has strong fluidity;
- Large flow window (FW), strong resin fluidity;
The influence of resin fluidity on board quality
When PG is long, RF is high, MV is low, or FW is long, the following situations may occur after pressing:
- There is a lot of resin flow and poor board thickness uniformity (easy to be thick in the middle and thin on the edge).
- White edges appear on the edges of the board due to low resin content.
- Skateboarding easily occurs.
- Easy to show texture.
- The resin content of the board is reduced, which affects the dielectric properties and insulation properties. Also,anti-CAF performance is poor.
- The internal stress of the plate is increased, and it is easy to twist and deform after pressing.
When PG is short, RF is low, MV is high, or FW is short, the following situations may occur after suppression:
- Dry board, trunk line, dry point.
- Air bubbles.
- The cohesive force between core material layers is weakened, and the board is prone to bursting.
- The peel strength between resin and copper foil is weakened.
PP storage conditions
- Storage temperature: 21±2℃ or below 5℃
- Storage humidity: below 60%
- Storage time: 90 days and six month
Key Points of Layer Stack-Up Control
-Placing the Board Along the Laser Beam
Our current lay up is two types. Controlling the consistency of lay up can ensure uniform force during pressing and avoid white edges due to loss of pressure. This requires the position of the laser beam to be adjusted and fixed when preparing for lay up. Laying the board along with the laser beam in the lay up production.
In the PCB design, if the removed area by the rout is large, a dummy pad is required to be added to the rout area to increase the residual copper rate and reduce the filling. The pad diameter is required to be 4.0mm, and the spacing is required to be 1.5mm.
- For designswith broken edges, dummy pads must be filled with a pad diameter of 1.5mm and a spacing of 1.0mm.
- lThe two layers of dummy pads corresponding to the inner layer board are required to be staggered by half the pad distance to balance the pressure during pressing
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 the pressure cooker, which is commonly used by the industry. In addition, in the multilayer 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.
It refers to the traditional lamination method of early multilayer PCB 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 significantly increased. The current method is the 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.
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