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Microwave Tech

Microwave Tech

Microwave Tech

Microwave Tech

High-Frequency Microwave and HDI board
2021-07-28
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Author:Fanny

With the development of electronic technology, the microwave high frequency and HDI board has been widely used in structural design.  New applications are emerging one after another, and have spread to national defense construction, scientific research, industrial and agricultural production, daily life, and other fields.  The high-frequency microwave characteristics of the printed circuit board are required, and the material requirements are inevitably higher and higher.  For high-frequency microwave printed board, the substrate used is completely different from FR-4 in glass fiber cloth and filler. At present, this high-frequency microwave material for high-density interconnect board production is still a stage of exploration.  Due to the difference in materials, abnormal problems such as plate explosion have appeared in the production process. This paper takes a plate multi-stage HDI ceramic plate as an example to introduce the key technologies in the production process.


1.Definition of microwave high-frequency

High-frequency microwave, as its name implies, is high frequency and short wavelength. To what extent, it is described quantitatively below.  Generally, the wavelength of 1 m ~ 0.1 mm, the corresponding frequency range of 300 MHz ~ 3 000 GHz electromagnetic wave is called microwave.  From the electromagnetic spectrum, the low-frequency end of the microwave is close to the ultrashort wave, the high-frequency end is adjacent to the infrared, so it is a very wide band, its width of 3 000 GHz, then all the ordinary radio wave width of the sum of thousands of times.

PCB


2. Process design

2.1 Process design before optimization

This plate is originally composed of two core plates, a semi-cured sheet, and copper foil superposition pressing. The blind holes are designed with overlapping holes. The blind holes are required to be filled and the copper thickness of the inner layer is a minimum of 34.3 μm (1 oz).

(1) Pressing for the first time (making L3~L6 layer resin plug hole).

Material opening → inner layer pattern → inner layer etching → inner layer AOI→ brown → pressing (L3/L6 laminating) → inner layer pattern 1→ inner layer AOI1→ brown 2

(2) The second pressing (L2~L7 layer, L2 and L7 layer blind hole).

Pressing 1 (L2/L7 laminating) → Browning 3→ laser drilling → slice analysis → Browning → inner layer copper precipitation → entire plate filling and electroplating → slice analysis → inner layer graphics → inner layer etching → inner layer AOI→ Browning 4

(3) The third time of pressing (making layers L1-L8, making blind holes of layers L1 and L8).

Press 2 (L1/8 laminating) → brown → laser drilling → slice analysis → brown → outer copper precipitation → whole plate filling electroplating → slice analysis → copper reduction → outer drilling → outer copper precipitation → full plate electroplating → outer figure → graphic electroplating → outer AOI→ Normal production


2.2 Optimized process design

The process can be simplified by pressing the core board with the scoreboard. Therefore, the original process needs to be redesigned. The new process design is as follows:

(1) Pressing for the first time (making L3~L6 layer resin plug hole).

Cutting → inner pattern (copper PAD corresponding to the blind hole of layer L2 and L7 needs to cut copper, and the diameter of cut copper is 0.075mm smaller than that of laser drilling diameter, but smaller than PAD) → inner etching → inner AOI→ Browning → pressing (l3/6 laminating) → inner pattern 1→ inner AOI1→ Browning 2

(2) the second pressing (making L1~L8 layer).

Pressing (L1~8 layers) → drilling laser positioning holes → blind hole window pattern (the diameter of the window is the same as that of the laser drill) → blind hole window etching → laser drilling → slice analysis → outer copper precipitation → whole plate filling and electroplating (the thickness of the copper in the hole is ≥20  Mm) → slice analysis 2→ outer hole plating pattern → spot plating and hole filling electroplating (blind hole filling) → slice analysis → film removal → sand belt grinding plate → outer hole drilling → outer copper precipitation → full plate electroplating → outer figure → graphic electroplating → outer AOI  → Normal production

At present, it is not mature enough for high-frequency microwave materials to be used in the production of multiple pressing of high-density interconnect boards. The production reference of a microwave high-frequency board made of ceramic materials made by our company is summarized as follows.

(1) The high-frequency microwave material pressing condition is higher than the ordinary FR-4, adjust the pressing program, plate arrangement method, etc., to solve the problem of pressing cavity caused by the material performance;

(2) The high-frequency ceramic plate semi-cured piece is composed of ceramics and colloid, the semi-cured piece contains very low glue, almost zero, the copper foil binding force is poor, the adhesion of copper foil is weak, by adjusting the pressure structure, to improve this problem;

(3) The high-frequency microwave plate is a ceramic material, the physical properties are brittle and hard, the traditional chemical removal method (KMnO4+H2SO4) bite erosion efficiency is low, by increasing the plasma removal of rubber to increase the amount of rubber, at the same time by adjusting the drilling parameters to improve the hole diameter and rubber removal;

(4) the microwave high-frequency board for curing bonding with copper foil, appear bubbles, instead to make code pressing, the blind hole for the pile hole, a laser, have the effect of the optimization process, reduce the palm in the process, the production cost of plating and outer process, at the same time under the condition of existing under the condition of artificial cost and material cost rise,  Can make a significant contribution to the company's efficiency improvement.