Flexible printed circuit board (FPC) is known for the advantages of softness, lightness, thinness and flexibility. As electronic products become smaller in size, lighter and thinner, FPC gradually replaces rigid PCB to be key component of products like Notebook computers, smartphones, camera, tablet etc. Traditional flex PCB materials are mainly based on the three-layer structure of PI film adhesive/copper foil. The adhesive is mainly Epoxy/Acrylic, but the adhesive has poor heat resistance ability and dimensional stability. Its 200°c maximum operating temperature sets a limit on its application,especially not fit for high reliability applications. For this reason, adhesiveless FCCL is a highly recommended option to produce high reliability, high density circuitry of flexible, rigid-flex, and all-flexible multilayer constructions.
Since the adhesiveless FCCL has no adhesive, it has excellent heat resistance, and the long-term use temperature can reach 300 or more. Figure 2 is at a fixed temperature of 200, the adhesiveless FCCL and three layers have glue The results of the relationship between the tear strength of the soft substrate and the time indicate that the tear strength of the non-adhesive soft substrate has very little change at high temperature for a long time, while the tear strength of the three-layered soft substrate decreases sharply in a short time at high temperature. Figure 3 shows the relationship between the tearing strength of the adhesiveless FCCL and the three-layer rubberized flexible board substrate against temperature. When the temperature of the adhesiveless FCCL is greater than 120, the tearing strength of the adhesiveless FCCL decreases sharply due to the deterioration of the adhesive. Generally speaking, the temperature of SMT soldering on the soft board is mostly over 300. In addition, the temperature of the pressing process in the production of the rigid-flex board (Rigid-Flex) is also as high as 200, which is not suitable for the three-layer flexible board substrate. These applications.
The dimensional change of the adhesiveless FCCL is very small by temperature, even if the dimensional change rate is still within 0.1% at high temperature (300 °C); but the dimensional change rate of the three-layer rubberized flexible board is greatly affected by temperature. Good full-inch stability will be of great help to the thin-circuit manufacturing process. Nowadays, high-end electronic products such as LCD, PDP, COF substrates, etc. emphasize thinning, high density, high size stability, and high temperature resistance. And reliability, so under the trend of consumer electronic products gradually becoming lighter, thinner and shorter, non-adhesive soft boards will become the mainstream of the market.
The adhesiveless FCCL has excellent chemical resistance properties, and the tear strength does not change significantly for a long time. However, the three-layer rubberized flexible board substrate has poor chemical resistance due to the adhesive, and the tear strength varies Time increases and decreases significantly. Other characteristics of the adhesiveless FCCL include the ability to reduce the thickness of the substrate, which is in line with the trend of lightness, thinness and shortness. In addition, because of the low chloride ion after etching, the ion mobility is reduced, and the long-term thin line is also Reliability.
Below we introduce three manufacturing methods for adhesiveless flexible copper clad laminate:
1) Sputtering electroplating method: PI film is used as the base material. After the PI film is plated with a layer of attribute layer by vacuum sputtering (Sputtering), the copper thickness is increased by electroplating. The advantage of this method is that it can produce ultra-thin adhesiveless FCCLs, and it can also produce double-sided flexible boards with different thicknesses.
2) Coating method: Using copper foil as the base material, the synthesized polyamic acid (Ployamic acid) is extruded and coated on the rolled copper foil with a precision die. After drying in an oven and imidization (Imidization) ) Form a adhesiveless FCCL. Coating method is mostly used for single-sided flexible board, if the copper thickness is less than 12.
2) Hot pressing method: First coat PI film with a thin layer of thermoplastic PI resin, first harden at high temperature, and then use high temperature and high pressure to remelt the thermoplastic PI. The thickness of the copper foil is also difficult to be less than 12 The manufacturing method of the rubber flexible board substrate, among which the sputtering plating method can best meet the ultra-thin requirements.
According to Mektec’s market estimates, in the next 5 years, the adhesiveless FCCL will gradually replace the three-layer adhesive xible board high-end flexible board market. Taking the Japanese market as an example, the market for the adhesiveless FCCL has already From 290,000 square meters in 1997 to 1.72 million square meters in 2000, the market scale has grown nearly 6 times, and the market share will increase from 3.4% to 16.8. In addition, the EU will completely ban halogen and lead in 2004. For product input of toxic substances, the adhesive-free soft board substrate eliminates the use of adhesives and does not need to use halogen-containing fuels. At the same time, it can meet the requirements of lead-free high-temperature manufacturing. It is the best choice for the industry.
Emphasizing that portable and user-friendly electronic products have become the mainstream of the market today. In the country, it has become the world’s second largest notebook computer production site, and the communications market is rapidly taking off. In the future, portable products will become lighter, thinner and more powerful. With the trend of high density, the market demand for ultra-thin adhesiveless FCCLs with copper thickness below 5 will be huge in the future.
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