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 You Need to Know Tips for Multilayer PCB Stackup

You Need to Know Tips for Multilayer PCB Stackup

Why do we choose Multilayer PCB Stackup?

Multilayer PCB trends are high speed, multifunction, large capacity, and small volume. With the continuous development of electronics technology. especially the extensive and in-depth application of large-scale integrated circuits. Multilayer printed circuit boards are rapidly developing to high density and high precision. micro-fine lines, small aperture penetration. such as blind buried holes, and high board thickness. aperture ratio, and other technologies to meet the needs of the market.


The Purpose of Multilayer PCB Stackup

The current multilayer PCB production process is to achieve the incremental layers and then stack them up together. At first, the inner board was finished. and then layer by layer by stack-up-fit for structured layer increase. To fully cure the material to increase the stability of the board between the layers Each lamination usually needs to reach a temperature of 175 °C and maintain it for more than 70 minutes. to achieve the standard lamination environment for the application of substrates plus the waiting time for the heating up and cooling down processes. Single lamination times are usually up to 4 hours or more. The more layers, the more laminations, and the longer the production cycle of the board.


What is A Multilayer PCB?

A multilayer PCB is a multi-layer alignment layer circuit board. For example, between every two layers, there is a thin dielectric layer. Multilayer PCBs have at least three conductive layers, two of which are on the outer surface, while the insulating board synthesizes the remaining layer. The electrical connection is usually achieved by plating holes. These holes are in the cross-section of the board. During production, each layer produced well. optical equipment and stacked together. Let the multi-layer circuit be stacked up on a piece of PCB. This is a multi-layer circuit board. Multilayer PCB types are multilayer rigid PCB, multilayer flexible PCB, and multilayer flexible PCB.

What are Benefits of Multilayer PCB?

The Multilayer PCB has many features. high assembly density, small size, lightweight. The high assembly density reduced the connections between the components. Thus improving reliability. At the same time, it increased the number of layers of wiring. thus increasing design flexibility. It can form a circuit with a certain impedance; it can also form a high-speed transmission circuit. There are also set-circuit and magnetic shielding layers. and metal core heat dissipation layers. That can be set to meet the needs of shielding, heat dissipation, and other special functions. and simple installation, high reliability.

But there are also some disadvantages to multilayer PCB. high product price; a long production cycle; and requires sophisticated testing methods.

The Production Process of Multilayer PCB

  • Opening-inner
  • Layer-lamination
  • Drilling-sink
  • Copper-line-figure
  • Electric-etching-solder
  • Resist-character-
  • Spray tin/sink golden
  • V-cut
  • Flying test
  • Vacuum packing

Types of Multilayer PCB Stackup

1. Kraft Paper For Multilayer PCB Stack-up

multi-layer er board lamination, more than the use of kraft paper as a heat transfer buffer. Place the kraft paper between the hot plate and the steel plate of the laminating machine. with a slope that is closest to the heating curve of the bulk material. so that it can easily stack-up multiple substrates. multi-layer plate between the layers of the plate to minimize the temperature difference. commonly used specifications for 90 pounds to 150 pounds.

2 .Kissing Stackup, Low Stack-up

When finished multilayer PCB stackup together. after the sheets are placed in each opening position. The temperature increased from the stack-up’s top column. and lifted upward from the bottom layer to stack-up the loose material into each opening for bonding. At the same time, the film for bonding starts to soften gradually and even flows. The stack-upure used for top extrusion cannot be too large. This method initially uses a lower stack-upure (15 to 50 PSI) called “kissing stack-upure”.

But when the resin softens in each film loose material by heat and gelatinization, it needs to be raised to full stack-upure (300  500 PSI), called “low stack-upure.”

3. Copper foil Stack-Duping Method

Refers to the mass-produced multilayer PCB. the outer layer of copper foil and film with the inner skin stack-uped together. to replace the traditional stack-up law of the early single-sided thin substrate.

4. Boil Stack-up Method

It is a kind of container filled with high-temperature saturated water. vapor and can apply high air stack-upure. The laminated substrate specimen was put in it. for a while to force the water vapor into the plate. and then remove the plate specimen and place it on the high-temperature molten tin surface. to measure whether it is separate for each layer.

5 Large stack-up board (lamination)

Use copper foil to pre-position on the inner laminate. and scanned for positioning after stack-uping. and then drill out the tool hole from its center to be set on the drilling machine for drilling.

6. Stacked-up Method

Before stack-uping multi-layer PCB or substrates. We need to prepare the inner board, film, copper skin, and other kinds of loose material. even steel, kraft paper padding. to complete the top-to-bottom alignment, to be able to be carefully sent into the stack-up for hot stack-uping. for the sake of mass production speed and quality. The 8 layers need to be in automated way. Many factories combine “laminating” and “folding” into a comprehensive processing unit. The automation project is quite complicated.

Guide for Multilayer PCB Stackup

We get the PCB board, you will find that the thickness is about 1mm. look carefully, in this 1mm thickness, you will see a lot of layering. PCB production is not a complete bare board production. It is made of many different materials, layer by layer, stack-uped together.

  1. The inner layer of the line production complex

multilayer PCB lines have high speed, thick copper, and high frequency. even high Tg value of various special requirements. The requirements for the inner layer. wiring and graphic size control are getting higher and higher. For example, ARM development board, the inner layer has many impedance signal lines. but also to ensure the integrity of the impedance. so it increases the difficulty of the inner layer line production.

  1. Alignment difficulties between inner layers

The number of layers of multilayer PCBs is increasing. and the alignment requirements of the inner layers are getting higher. if under the influence of temperature and humidity in the workshop environment. The film will rise and shrink. and the core board will also rise and shrink to a certain extent after production. which makes the alignment accuracy between the inner layers more complicated.

  1. Difficulties in the stack-uping process:

The stacking of multiple core boards and PP is prone to delamination. slippage and vapor pack residue when stack-uped together. In the process of designing the structure of the inner layer. we should consider the thickness of the dielectric between the layers, and the flow of glue. also contain the heat resistance of the sheet and other factors. and design to the corresponding stack-uped structure.

  1. Difficulties in drilling production

Multi-layers made of high Tg or other special plates. The roughness of the drilling of various materials is different. which increases the difficulty of removing the glue slag in the hole. Due to the high-density multilayer PCB. The production efficiency is low and it is easy to break the knife. and between different networks of over-holes The hole edges being too close to each other will lead to a CAF effect problem. So, the spacing between the hole edges of different networks was kept at 0.3mm.

Factors Affecting the Quality of Multilayer PCB Stackup 

Many customers lack understanding of the laminating process. It often happens after getting the multilayer PCB. we found that PCB warped edge. rolled circles and the board has the obvious problem of delamination. There are even serious quality problems, such as the existence of the inner layer of broken roads. A big reason is a piece of equipment. process and there are many defects, resulting in uncontrollable laminating quality.

Have advanced production equipment

The stack-up machine can accurately control the heating and cooling of the hot plate. the thermal cycle and liquid stack-upure, temperature control. Through the operation of the cold stack-up. it can effectively eliminate stress. to carry out each stack-up lamination in an efficient and high-quality way.

And the equipment has excellent processing accuracy. thus guaranteeing the reliability and low failure rate of equipment production. Together with high hardness and flat imported steel plate. raw material, high-quality PP sheet (bonding sheet), and supporting professional equipment. it can effectively avoid process defects and improve stack-up lamination quality. Such as.

Avoid excessive glue flow. uneven glue content between inner layers leading to board warping. delamination and other process defects, guarantee the high yield of multi-layer lamination!

Very low failure rate and precision automation control can reduce production risk. maintain efficient and stable production, saving time for customers!

Quality of laminated steel plates

Steel plate is one of the core accessories of lamination. such as insufficient hardness, poor flatness, etc. will cause damage to the process, such as laminated thickness tolerance precision is not high. The board surface has an indentation, etc. GESP PCB adopts imported mirror steel plates. It has high hardness, high toughness, heat resistance, stack-upure resistance, and wear resistance. It can resist thermal expansion and contraction in the handling process of collision. friction caused by deformation and scratches. Even if stack-uped together, the steel plate can still maintain a very high flatness.

high-precision X-ray target drilling machine, hot melt machine, and PP bonding sheet.

X-RAY drilling target machine used for alignment between layers after lamination. The principle is that after the lamination of multilayer plates The X-Ray is used to judge the alignment between the inner layers and the punch positioning holes.

The hot melt machine is used to bond the PP to the core board through high temperature and stack-upure. The common riveting processing together. the accuracy of the alignment between layers affected the tolerance of the rivet holes. and the impact of the stack-uped together will lead to the deformation of the rivet and cause the deviation between layers.

PP bonding sheet:

PP sheet is a sheet material. in which the resin is in the B-phase, under the effect of temperature and stack-upure. it has fluidity and can quickly cure and complete the bonding process. and form the insulation layer together with the carrier.

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