PCB Tech - Multilayer circuit board production

The manufacturing process of multilayer circuit boards is currently mostly a subtractive method, that is, the excess copper foil on the raw material copper clad board is subtracted to form a conductive pattern. The method of subtraction is mostly chemical corrosion, which is the most economical and efficient. Only chemical corrosion does not attack, so it is necessary to protect the required conductive pattern. A layer of resist must be coated on the conductive pattern, and then the unprotected copper foil is corroded and subtracted. In the early days of resist, the resist ink was printed in the form of a circuit by screen printing, so it was called "printed circuit". However, as electronic products become more and more sophisticated, the image resolution of the printed circuit cannot meet the product requirements, and then photoresist is used as an image analysis material. Photoresist is a photosensitive material that is sensitive to a certain wavelength of light source and forms a photochemical reaction with it to form a polymer. It only needs to use a pattern film to selectively expose the pattern, and then pass it through a developer solution (example 1% carbonic acid) Sodium solution) strips off the unpolymerized photoresist to form a patterned protective layer.

In the current multi-layer circuit board manufacturing process, the interlayer conduction function is realized through metallized holes. Therefore, drilling operations are required in the PCB manufacturing process, and the holes are metallized and electroplated, and finally realized Conduction between layers.

The manufacturing process of multi-layer circuit boards is summarized as the conventional six-layer PCB manufacturing process:

1. Make two non-porous double panels first

Cutting (raw material double-sided copper clad laminate)-inner layer pattern production (form pattern resist layer)-inner layer etching (minus excess copper foil)

2. Adhesive and press the two fabricated inner core boards with epoxy glass fiber prepreg

The two inner core boards and the prepreg are riveted together, and then a piece of copper foil is laid on both sides of the outer layer and pressed under high temperature and high pressure with a press to make them adhered and combined. The key material is a prepreg. The composition is the same as that of the original material. It is also epoxy glass fiber, but it is not fully cured and will liquefy at a temperature of 7-80 degrees. A curing agent is added to it, which will interact with the resin at 150 degrees.

The crosslinking reaction cures and is no longer reversible afterwards. Through such a semi-solid-liquid-solid conversion, adhesive bonding is completed under high pressure.

Three, conventional double panel production

Drilling-copper sinking (hole metallization)-outer circuit board (forming a patterned anti-corrosion layer)-outer layer etching-solder mask (printing green oil, text)-surface coating (tin spraying, immersion gold, etc.)- Forming (milling and forming).