PCB process design principles

乱世煮酒论天下

PCB process design principles [Copy link]

The design and manufacture of single-sided boards, the main body of which is a hard insulating material, epoxy resin fiberglass or FR4, called the substrate, and the copper material is attached to one side of the circuit board by gluing or electrodeposition, called the top surface.

Lithography technology principle process:

1. The copper metal layer is coated with a photosensitive material called photoresist;

2. The photoplotter uses a light source to selectively expose portions of the photoresist;

3. The chemical properties of the photoresist change after exposure. If the photoresist is a positive film, it will soften after exposure. If the photoresist is a negative film, it will become solid after exposure.

4. The softened photoresist is removed using a developer, while the hardened photoresist remains, covering a portion of the surface of the metal layer;

5. The exposed copper layer is removed using strong acid chemicals, a process called etching;

6. Remove the remaining photoresist, and what remains is the copper metal layer pattern;

7. Cover the circuit board (except the pads) with a solder mask, apply solder paste on the pads, use the silk screen layer to print text and draw symbols; (this step is the post-processing process)

Double-sided board manufacturing process:

The manufacturing process of double-sided boards is similar to that of single-sided boards. Copper metal layers are attached to both sides of the substrate, and the processing process of each side is similar to that of single-sided boards. The important difference between double-sided boards and single-sided boards is that electrical connections are required between the top and bottom surfaces, and this connection is called a via.

Manufacturing process of multilayer board:

The manufacturing process of multi-layer boards is similar to that of double-layer boards. A group of double-layer boards are pressed together using prepreg. Prepreg is similar to glue. Initially, the prepreg is soft, but becomes very hard after high temperature and pressurization. The core board and prepreg parts of the multi-layer board are called the laminate of the circuit board.

Look at the distribution of the multi-layer board below. It is an eight-layer board made of three double-layer boards with semi-cured sheets. The top and bottom layers are attached to the surface of the semi-cured sheets. Is the effect and process of sticking on the semi-cured layer the same as sticking on the substrate?

There is also the hardening and removal process of photoresist. What do the positive and negative photoresists mean? How can the photoresist after the positive film has hardened be removed?

maychang

[The design and manufacture of single-sided boards. The main body of a single-sided board is a hard insulating material, such as epoxy resin fiberglass or FR4, which is called the substrate. The copper material is attached to one side of the circuit board by gluing or electroplating, which is called the top surface. ]

The copper-clad surface of a single-sided board is the bottom surface , not the top surface .

乱世煮酒论天下

maychang posted on 2024-6-16 11:19 [Design and manufacturing of single-sided boards. The main body of the single-sided board is a hard insulating material, which is epoxy resin glass fiber or FR4, called the substrate. The copper material is passed through...

There is a question. For some PCBs that need to pass large currents, not only do they need to be able to pass larger currents, but they also need a higher heat dissipation level. According to the current carrying capacity of copper thickness of general PCBs, 1mm width and 1oz thickness of copper can pass 1A of current. So when large currents need to be passed, there are two ways to do it: increase the width and thickness of the copper. The width of the copper is limited by the size of the PCB, while the thickness of the copper can be increased a lot. Is it possible to increase the thickness of one layer of copper on each layer of the multilayer board at the same time, and connect all the layers with pile holes? Will this increase the overall thickness of the PCB a lot?

maychang

Luan Shi Zhu Jiu Lun Tian Xia published on 2024-6-16 15:32 There is a problem. For some PCB boards that need to pass large currents, not only do they need to be able to pass larger currents, but they also need a larger heat dissipation level...

Is it possible to add a layer of copper thickness to each layer of a multilayer board at the same time and connect all the layers with stakes?

Can't.

乱世煮酒论天下

maychang posted on 2024-6-16 15:35 [Is it possible to add a layer of copper thickness to each layer of a multilayer board at the same time and connect all the layers with stake holes? ] No.

Why can't this be done?

maychang

Talking about the world in a chaotic world published on 2024-6-16 15:52 Why can't we do this?

Why can’t we do this?

The vias in the circuit board are plated into the holes in the circuit board using the chemical plating method. The cross-sectional area of the conductor is much smaller than the cross-sectional area of the wire on the circuit board, so it cannot pass large currents. Even if multiple vias are arranged, their current carrying capacity is much lower than, for example, a 4mm wide wire.

乱世煮酒论天下

maychang published on 2024-6-16 16:00 【Why can't this be done? 】 Circuit board vias are plated into the holes of the circuit board using a chemical plating method. The cross-sectional area of the conductor is much larger than that of the conductor on the circuit board...

I mean increasing the copper thickness in each layer. For example, 0.5 or 1 oz is used for signal transmission, and 2 oz or thicker is used for high voltage transmission.

maychang

乱世煮酒论天下Published on 2024-6-16 20:01 I mean to increase the copper thickness in each layer. For example, 0.5 or 1 oz is used for signal transmission, and 2 oz or thicker is used for strong current transmission

What you said on the 3rd floor was [Is it possible to add a layer of copper thickness to each layer of a multilayer board at the same time, and connect all the layers with stake holes? ] My reply on the 6th floor was about vias.

maychang

乱世煮酒论天下Published on 2024-6-16 20:01 I mean to increase the copper thickness in each layer. For example, 0.5 or 1 oz is used for signal transmission, and 2 oz or thicker is used for strong current transmission

[If the signal cable is 0.5 or 1 oz, and the high-voltage cable is 2 oz or thicker]

Since the via cannot pass a large current, we can only find a solution on the copper foil on one side. However, the double-sided boards provided by the board factory must be the same thickness on both sides, and there is no way to make one side thinner and the other thicker.

maychang

乱世煮酒论天下Published on 2024-6-16 20:01 I mean to increase the copper thickness in each layer. For example, 0.5 or 1 oz is used for signal transmission, and 2 oz or thicker is used for strong current transmission

Instead of worrying about the thickness of the copper foil, it is better to solder copper wire on the circuit board wire to increase the wire cross-sectional area. Some low-power switching power supplies do this.

Of course, this is not a good solution, it can only be a makeshift one.

marginalzone

Luan Shi Zhu Jiu Lun Tian Xia published on 2024-6-16 15:32 There is a problem. For some PCB boards that need to pass large currents, not only do they need to be able to pass larger currents, but they also need a larger heat dissipation level...

In the current process, the inner layer copper thickness is usually up to 2Oz, and the outer layer can be electroplated thicker. If a large current is required, the vias can be filled with copper paste. These measures can improve the PCB's current capacity. You will know after talking to a few more board manufacturers.