The process of using resin plugs for high-frequency circuit boards is often due to BGA parts, because traditional BGA may make VIA between PAD and PAD to the back of the wiring, but if the BGA is too dense and the VIA cannot go out, you can directly The PAD is drilled and made via to another layer for routing, and then the hole is filled with resin and copper-plated to become PAD, which is commonly known as the VIP process (via in pad). If you only do via on the PAD without plugging the hole with resin, then It is easy to cause leakage of tin, leading to short circuit on the back and empty soldering on the front.

    The process of high-frequency circuit board resin plugging includes drilling, electroplating, plugging, baking, and grinding. After drilling, the hole is plated through, then the resin is plugged and baked, and finally it is ground and polished. Because the resin does not contain copper, another layer of copper is needed to turn it into PAD. These processes are done before the original high-frequency circuit board drilling process, that is, the fortress holes are processed first, and then Drill other holes and follow the normal process.

    If the plug hole of the high-frequency circuit board is not properly plugged and there are bubbles in the hole, because the bubbles are easy to absorb moisture, the PCB circuit board of the high-frequency circuit board may burst when it passes through the tin furnace, but if the hole is plugged in the process If there are bubbles, the bubbles will squeeze out the resin during baking, resulting in a situation where one side is recessed and the other is protruding. At this time, defective products can be detected, and high-frequency circuit boards with bubbles will not necessarily burst because of the failure of the board. The main reason is moisture, so if the board or board that has just been shipped from the factory has been baked when it is loaded, generally speaking, it will not cause the board to burst.

Shenzhen Apollo Precision Electronic Co., Ltd has factory that is mainly engaged in the production services of high-frequency microwave radio frequency induction printed circuit boards and double-sided multilayer circuit boards for quick samples and small and medium batches. The main products are: PCB high frequency board, Rogers circuit board, high frequency circuit board, high frequency microwave board, microwave radar antenna board, microwave radio frequency high frequency board, microstrip circuit board, antenna circuit board, heat dissipation circuit board, high frequency and high speed Circuit board, Rogers/Rogers high-frequency board, ARLON high-frequency board, mixed dielectric laminate, special circuit board, F4B antenna board, antenna ceramic board, radar sensor pcb, special circuit board manufacturer, pair of slot antenna, RF antenna, broadband Antennas, frequency sweep antennas, microstrip antennas, ceramic antennas, power splitters, couplers, combiners, power amplifiers, dry amplifiers, base stations, etc.

Recent years have been witnessing improvement in electronic information technology and increasingly higher demands from people on their applications of electronic products. Complex structure and multiple functions of electronic products lead printed circuit boards (PCBs) to move towards new directions. On one hand, increasingly more integrated components in electronic products and miniaturization of overall size make circuit boards be of high density, high accuracy and high integration, which arousing a transition from simply multilayer PCBs to HDI PCBs. On the other hand, electronic products call for high-speed, low loss, low delay and high-fidelity (HiFi) signal transmissions and have to be compatible with high-consumption environment for high powers, requiring PCBs to be involved with a high-frequency and high-dissipation thermal design and high-quality signals transmission.

To cater to the demands and market trend, technologies concerning high frequency, high thermal dissipation and high density interconnect designs have been receiving the most attention in modern PCB industry and will be a leading development trend in the future.

In this article, we take an 18-layer PCB (a multilayer circuit board containing participation of numerous advanced designs including multiple back drilling, high aspect ratio resin-plugged via and high-thermal dissipation via) with high-frequency material as a study example, to detail technologies applied in the process of this circuit board fabrication, such as resin-plugged via, stacking up, high-density drilling and back drilling.

High-Frequency and High-Speed Multilayer PCB Structure Features and Materials

Structure Features

In order to be fully aware of structure features of high-frequency and high-speed multiplayer PCBs, the following table and figure can be referred to.

Substrate Material

High frequency, signals with a frequency band to be at least 300MHz (equivalent to wavelength no more than 1m), can be further classified into medium frequency (MF) and very high frequency (VHF) according to different wavelengths. Electromagnetic waves whose wavelength is at least 1GHz are usually referred to microwaves. As PCB's majority functions are determined by substrate material, substrate material featured by high frequency will be applied in high-speed and high-frequency PCBs. High-frequency substrate material has to meet the following demands:
a. Dielectric constant (Dk) should be small and stable (generally speaking, the smaller, the better). Based on principle which signal transmission rate is inversely proportional to square root of material dielectric constant, high dielectric constant tends to cause delaying signal transmission.
b. When it comes to signal transmission quality, dielectric loss (Df) should be small as well. The smaller Dk is, the smaller signal loss will be.
c. Copper foil should have a surface with low roughness to avoid impedance control mismatching and signal loss caused by skin effect.
d. Substrate material for high-frequency and high-speed PCBs should feature low hydroscopicity. Dielectric constant of water is 70 and this number will be increased when substrate absorbs more moisture. Thus, modification of impedance control will lead to badly-performed signal transmission.
e. Copper foil should conform to relatively high peel strength that mustn't be compromised just due to low surface roughness.
f. Substrate material should also perform excellently in terms of size stability, heat resistance, chemical resistance, impact strength and manufacturability.

In conclusion, much care has to be taken with above aspects and items considered when deciding suitable substrate material for high-frequency and high-speed multilayer PCBs. For example, the following table details comparison between substrate materials provided by different distributors.

Based on integrated comparison in terms of substrate material dielectric constant, dielectric loss, Tg, ion-migration resistance, moisture resistance, manufacturability and cost, we use Material C for this type of high-frequency and high-speed multilayer printed circuit board.