Application Watch: R&D on ultrathin flexible PCBs for wearables continues

Flexible PCB makers leverage an expanding market in wearable electronics to enhance miniaturization capability.

Flexible PCBs or FPCBs provide an efficient interconnectivity solution in superthin and lightweight configuration, which meets the miniaturization requirement in various electronics products. Because of this advantage, these saw significant growth in recent years and will keep benefitting from strong demand for compact and flexible devices.

The boom in wearable electronics, in particular, has raised the stakes for the FPCB category, and will spur R&D toward ultrathinner boards with finer pitches. In coming years, the minimum line width/spacing is expected to shrink to 1.97mil and possibly 0.9mil, and hole sizes can be as small as 0.1mm or even 0.05mm.

To keep up with upgrades in the industry, China suppliers of flexible boards are working to improve their fabrication processes. Zhuhai Chuangyan has come up with a new ion implantation or electroplating technology to churn out a high-performance nonadhesive 2-layer copper-clad laminate for FPCBs for wearable devices. The base material measures 1 to 12µm in thickness.

Companies are also directing efforts toward circuit boards with six to eight layers. They anticipate such multilayer types will be in demand in the years ahead.

Robust wearables industry

In addition to product development, the highly positive outlook for the wearables application market is encouraging local manufacturers to invest further in the flexible PCB line.

Zitrok Electronic Co. Ltd, which increased its output by 15 percent in 2019, will continue with expansion in coming months. Shenzhen Hualin has allocated $176 million for the construction of a new facility for flexible PCBs in the Nanchang New & High-tech Industrial Park. From the project, it looks to realize as much as $764 million total sales value in the next five years.

The wearables market has experienced a surge, with an estimated 305.2 million units shipped worldwide in 2019 compared with 178 million units in 2018, according to IDC. Of this, earwear represented 139.4 million, smart watches 69.3 million and wristbands 68.2 percent, and others the rest. The first excludes audio-only devices and covers devices with smart assistant, health and fitness tracking, or audio enhancement functions.

In 2023, shipments will hit 489.1 million units, which IDC attributes to the rise in the supply of wearables and decreasing prices. Earwear devices will account for 56 percent or 273.7 million, smart watches about 22 percent or 109.2 million and wristbands at least 14 percent or 69.7 million.

China's deliveries of wearable electronics will see an increase of more than 30 percent in 2020 and through 2021.

Wearables FPCB shipments

About 200 makers of flexible PCBs in China offer selections for wearable devices. The application represents between 30 and 60 percent of shipped volume of local enterprises at present.

Besides flexible circuit boards, domestic and foreign companies there turn out rigid and rigid-flex types, and PCB assemblies widely used in mobile and automotive electronics, communications products and medical equipment.

More than two-thirds of the manufacturers are in the Pearl River Delta region, specifically in the cities of Shenzhen, Dongguan, Zhongshan, Xiamen, Suzhou and Changzhou. There are also companies in other locations such as Chengdu in the southwestern province of Sichuan, where labor cost is lower. These areas will continue to attract suppliers looking to enter the PCB line.

Up to 8 layers

Mainstream flexible PCBs for wearable devices in China come in variants with a maximum of eight layers. These use a polyimide or Mylar base material and 0.018, 0.035, 0.07 or 0.1mm-thick copper foil, and have a 3mil minimum line width and spacing. Board thickness ranges from 0.025 to 0.1mm. Products are compliant with RoHS.

Most makers highlight capability for various customization requirements, noting over two-thirds of their shipments are based on buyers' specifications.

Polyimide, Mylar, copper, adhesive and other materials usually come from the local supply, mainly Shengyi. Companies turning to foreign providers source mostly from Thinflex, Toray, GE Plastics and Bayer.

The cost of manufacturing inputs has not fluctuated significantly in past months, ensuring prices of flexible PCBs remain stable. This trend is expected to cover over in the near term. Some makers, however, may lower their quotes to counter competition.

The products in this gallery have been handpicked by our China-based market analyst for representing current trends in flexible PCBs from China makers.

Flexible PCB with up to 8 layers

The FPC Electronic Board model from Dalian JY Electronics & Technology Co. Ltd is a flexible PCB that comes in up to 8-layer versions and meets IPC Class 2 standard. It has 3mil minimum line width and spacing, as small as 0.2mm holes and ±0.05mm tolerance. The board measures 6x6mm to 400x500mm. Options for surface finish include HASL, lead-free HASL, immersion tin, gold finger and OSP.

The negotiable minimum order has a 15-day delivery lead time.

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4-layer flexible PCB with immersion gold

Full Years Technology Co. Ltd's 4-layer flexible PCB, FPC-1 model, adopts a 1mil polyimide base material and coverlay, immersion gold surface finish and 1oz copper.

The minimum order is negotiable and has a delivery lead time of 7 days.

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Flexible PCB adopts polyamide, polycarbonate base

Based on 1/2, 1, 2, 3 to 5mm polyamide and polycarbonate materials, the model HL-100 flexible PCB from Honlex Flexible PCB Industrial Co. Ltd has 4mil minimum line width and spacing, as small as 0.3mm holes and SnPb, nickel or gold plating.

The order quantity is negotiable. Delivery lead time is 7 days.

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2-layer polyimide flexible PCB

The Zitrok-PCB2019060506 model from Zitrok Electronics Co. Ltd is a 2-layer flexible PCB based on a 0.1mm polyimide base material.

The minimum order is negotiable. Delivery takes 6 days.

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