SunKey Successfully Develops Advanced 14-Layer 6-Stack Any-Layer HDI PCB

SunKey Successfully Develops Advanced 14-Layer 6-Stack Any-Layer HDI PCB

I.Foreword

Since 2019, the company has keenly recognized the explosive growth in demand for high-density interconnects and high-frequency, high-speed boards from industries such as 5G communications, industrial control, computing storage, and consumer electronics. Therefore, we have further upgraded and adjusted our product strategy. Over the past four years, we have gradually achieved stable mass production of 1st to 5th layer HDI boards. Now, our group's technology center has made another breakthrough, successfully developing a 14-layer 6-orderlayer arbitrary layer interconnect HDI board. Utilizing technologies such as arbitrary layer interconnect (ELIC) and laser blind vias, this significantly improves wiring density and ensures high-frequency signal integrity, helping customers overcome bottlenecks in miniaturization and high performance. This provides highly reliable PCB solutions for 5G base stations, AI servers, and high-end industrial control equipment.

II. Overview of Any-Layer Interconnect HDI Board

The 5G wave is driving the upgrading of PCB manufacturing processes! The performance of traditional HDI boards has hit a bottleneck, while Anylayer HDI boards, with their multi-layer architecture, ultra-fine line width and spacing, and robust module-carrying capacity, have emerged as the core solution for 5G terminal devices.

First adopted in Apple’s iPhone series, this technology is now widely integrated into the 5G flagship models of Huawei, OPPO, vivo, Xiaomi and other brands, evolving into a standard configuration for premium terminals.

SunKey predicts that mainstream 5G smartphones will adopt 8–12 layer 2nd-order HDI motherboards in the future, while flagship models will upgrade to 14 layer 3rd-order and higher-spec Anylayer HDI boards.

Currently, SunKey technical capabilities in this field rank among the leading positions among domestic private enterprises..

III. Introduction to Key Process Technologies of 14-Layer 6th-Order HDI Board

Any-layer HDI (Any-layer Interconnection) is a high-density interconnection technology with significant technical barriers. Its key manufacturing challenges include interlayer alignment, laser drilling, via filling and electroplating, as well as fine-line processing. Currently, there are very few Chinese manufacturers that possess both advanced process production capabilities and rapid delivery efficiency.

SunKey Electronics has been closely monitoring market trends. To address customers’ urgent demand for high-layer count, high-order any-layer HDI boards, the company successfully developed 14-layer, 6th-order any-layer interconnection boards in June after overcoming numerous technical hurdles, and delivered the products to customers in batches as scheduled.

1. Analysis of HDI Stack-up Structure

Conventional products in the industry are 1st–3rd-order HDI boards. The higher the order, the greater the risk of layer misalignment. This product is a 6th-order 14-layer board with a finished thickness of 1.6 mm. Its blind via structure adopts the 6+N+6 configuration, including 14 types of blind vias: 1-2, 1-3, 1-4, 1-6, 1-7, 1-9, 1-10, 1-11, 6-10, 6-14, 7-14, 10-14, 12-14 and 13-14. These blind vias enable electrical interconnection and must be fabricated through 6th-order HDI processes, featuring an extremely complex structure and a long manufacturing process. (See Figure 1)

2.Via Connection Method

Conventional core boards require 3 laminations (multiple laminations will lead to uncontrollable expansion and contraction of the core board). This product requires 6 laminations. This is achieved by 6 cycles of stacking and laminating the core boards of Layers 7 and 8, coupled with 6 rounds of laser drilling and plated via filling processes. Among them, the vias on Layers 7 and 8 are electroplated filled through-holes with a diameter of 0.15 mm, whereas all other vias are laser-drilled vias with a diameter of 0.1 mm, which are then electroplated and filled. (See Figure 1)

Figure 1 Structure and Cross-Sectional Views of 6-order HDI Board

3. Circuit Pre-compensation Coefficient

Six laminations make pre-compensation a critical consideration. It is necessary to account for the expansion and contraction induced by each lamination cycle to define the pre-compensation coefficient for the initial core boards (Layers 7 and 8). This coefficient directly impacts the subsequent fabrication of the board.

4. Laser Drilling

After the first two lamination processes for Layers 6&9 and 5&10, the coefficient values are relatively large. This causes the laser drilling machine and LDI machine to fail to achieve accurate hole recognition and alignment. Therefore, it is necessary to adjust the laser target parameters of the laser drilling machine and the operating parameters of the LDI circuit imaging machine.

5. Plated Via Filling

The number of 0.1mm laser-drilled vias ranges from 1,200 to 1,800 per side. The limited plating area tends to cause local indentation during via plugging and filling. This process requires 6 repeated process cycles of laser drilling and via filling.

6. Pattern Plating

The inner layer line width/spacing is 0.075/0.075 mm. The pattern distribution across the board is sparse and isolated, which tends to cause dry film residue and line width reduction during pattern plating and etching processes.

Figure 2 Appearance Display of 6-Level HDI Board

IV. Introduction to HDI Rapid Delivery Assurance Capabilities

1. We have invested heavily in equipment upgrading and replacement. In recent years, the company has successively procured HDI board-specific equipment including LDI (Laser Direct Imaging) systems, laser drilling machines, plated via filling lines, and controlled-depth drilling machines.

Notably, in 2019, we phased out all of our existing electroplating equipment in one go and completed a full-scale equipment upgrade and replacement. The upgraded portfolio covers chemical copper plating lines, primary copper plating lines, secondary copper plating lines, via filling lines, vacuum SES alkaline etching lines, vacuum DES acid etching lines, in-line etching AOI (Automated Optical Inspection) systems, vertical vacuum resin plugging machines, ceramic substrate grinding machines, 300℃ high-temperature multi-layer board PIN LAM presses, high-frequency electromagnetic bonding machines, as well as specialized hard gold plating lines tailored for HDI optical module boards.

2. In the raw material selection process, SunKey Electronics adheres to the core principle of ensuring the quality of customers' products and exclusively adopts premium raw materials from world-leading brands. Specifically, our base materials are high-end products sourced from top-tier manufacturers including ITEQ, NOUYA, Isola, Panasonic, Rogers and EMC; our chemical solutions are procured from industry benchmark enterprises such as Rohm and Haas and Atotech; our dry films are supplied by Japan’s Asahi Kasei and America’s DuPont; and our solder mask ink is provided by Sun Ink.

By leveraging the stringent quality control standards of high-grade raw materials, we fully meet customers' core requirements for superior quality and high reliability of high-end products.

V. Types of HDI Board Layer Stack Structures

SunKey is capable of manufacturing all the laminates listed below.