Application Watch: Future of flexible PCBs for wearables in additive printing technology

In recent years, printing technologies have been developed to improve the production of flexible circuit boards. One that is gaining traction is flexible printed electronic technology. Unlike traditional subtractive photo etching, which involves the removal of excess copper using liquid chemicals, this new method enables printing of precise circuit patterns on baseboards quickly and effectively. This simplifies the process while avoiding wastage of materials, such as copper, and eliminating the use of chemical baths, disposal of which impacts the environment.

In China, large companies, including BOE in its wearable displays, have started adopting flexible PCBs fabricated using this additive technology. More are expected to follow this lead and encourage flexible PCB manufacturers to keep up with the growing market for mobile electronics and wearable electronic devices.

Shipments of wearable electronic products are forecast to reach as high as 252.3 billion units in 2021, increasing 21.5 percent YoY, according to IDC. This is from 207.5 million in 2020 and 170 million in 2019. Based on available data from Gartner, the world's wearables market scale was $52 billion in 2020, rising by 27 percent over the previous year.

A similar upward trend is forecast for China's wearable devices industry, with total market scale to climb to $8.92 billion in 2022 from $3.82 billion in 2017, according to the China Industry Information Database.

In response, many Chinese suppliers of flexible PCBs will continue to boost production in the months ahead, according to those interviewed by Global Sources Electronic Components. Despite the pandemic, Shenzhen Lat PCB Co. Ltd raised its output by 30 percent in 2020. It plans to build a new factory in Yiyang, Hunan province. The facility, which will have a total area of 386,860sqm, is expected to raise Shenzhen Lat's output by 150 percent.

China is the world's largest production hub for flexible PCBs, accounting for more than half of global shipments. Xiamen Hongxin, Kingwong, Leader-Tech, JCD and SDG are some of the major homegrown companies. Their foreign counterparts include Nippon Mektron, Sumitomo Denko and Nitto Denko of Japan, and South Korea's Interflex. Most have more than one factory in China.

Over half of this manufacturing pool is in the provinces of Guangdong and Fujian, specifically in Shenzhen, Dongguan, Zhongshan, Huizhou, Zhuhai and Xiamen. There are also suppliers in Suzhou, Kunshan and Changzhou in Jiangsu, and Shanghai. Many can also be found in Hunan and Hubei provinces, where labor costs are lower than in the coastal areas.

Up to eight-layer flex circuits

Next releases of flexible PCBs for wearable devices will have line width and spacing of 50µm and hole sizes of 0.1mm and below, while HDI types are expected to remain hot in this category.

Manufacturers, such as Kunshan Captronics Jinye, have introduced double-sided HDI flexible PCBs.

For the majority, however, the typical selection for wearable devices consists of single-sided, double-sided and up to eight-layer flexible PCBs. These RoHS-compliant boards have 3mil minimum line width and spacing, 0.018, 0.035, 0.07 and 0.19mm copper, and 0.025mm to 0.15mm board thickness. The usual surface treatment options are immersion gold and silver.

Materials such as polyimide, Mylar, copper, gold, silver and adhesives come from domestic or foreign providers, depending on buyers' specifications. The main sources include Thinflex, Toray Films and homegrown company Shengyi.

No increases are expected in material costs and product prices in 2021, according to manufacturers interviewed. It is possible some suppliers will reduce quotes by up to 5 percent to counter competition.

Flexible PCB with RA, ED copper

This UL-listed Sculpture FPCB from Flex Plus (Xiamen) Co. Ltd has 1/2 or 1mil copper-clad polyimide and 1/3, 1/2 or 1oz rolled-annealed or electrodeposited copper, 1/2 or 1mil polyimide coverlay, 25, 30 or 35µm adhesive and electrolytic gold plating.

The minimum order quantity is 100 units. Delivery takes seven days.

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Single-sided to multilayer flexible PCB

Poe Precision Electronics Co. Ltd's POE-091002-02780-4862 flexible PCB is available in single-sided, double-sided and multilayer variants. It is UL-listed and RoHS-compliant.

The negotiable minimum order quantity has a delivery lead time of five days.

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Flexible PCB with 100,000-cycle flex life

This 018-0052 FPC-4664 from Shenzhen Lat PCB Co. Ltd is a double-sided flexible PCB that can withstand bending up to 100,000 times.

The 1,000-unit order quantity has a 10-day delivery lead time.

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Flexible PCB with as small as 0.2mm holes

Tortai Technologies Co. Ltd markets this GS-825-6155 flexible PCB with 1.96mil minimum line width, 3.93mil minimum line spacing and 0.2mm minimum hole size. Board thickness is 0.11 to 0.5mm.

The unit has a polyimide base, 1/2oz copper, immersion gold surface finish and white, yellow or green solder mask.

Order quantity is negotiable. Delivery is within 12 days.

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