Due to the high speed and high frequency of 5G, in order to ensure reliability and reduce signal loss during transmission, 5G communication has higher requirements for the dielectric constant and dielectric loss factor of the antenna material. At present, the flexible circuit board (FPC) substrate used in mobile phone antennas in the 4G era is mainly polyimide (PI), which takes into account PI’s excellent mechanical strength, bending performance, continuous stability, heat resistance, and insulation Features and other advantages. However, due to the large water absorption rate of the PI substrate, the dielectric constant (Dk) and dielectric loss factor (Df) are also large, especially for products with operating frequencies exceeding 10GHz, which makes it difficult to meet the requirements of antenna materials in the 5G era .
There are currently two mainstream solutions: modified PI (MPI) or LCP. MPI has certain comprehensive advantages in Sub-6G. However, as the commercialization of 5G advances, the millimeter wave stage will still be based on LCP. In terms of transmission reliability, LCP>MPI>PI; in terms of moisture resistance, LCP>MPI>PI; but in terms of cost, currently LCP film is subject to product yield and film supply monopoly, with the highest cost and lowest economy, while PI film is a mature The application product has the lowest cost, but it cannot be used for antenna transmission in the 5G era.The modified MPI can compete with the LCP in the Sub-6G stage, but the loss in the millimeter wave band is further widened compared with the LCP. Therefore, in the millimeter wave stage, the LCP will still be the main antenna film material. This will be elaborated below.
Low dielectric loss and extremely low water absorption gives LCP material excellent signal transmission performanceCompared with PI, LCP can greatly reduce high-frequency transmission loss. According to data from Sumitomo Electric Industries, LCP and PI materials have lower transmission loss at 5GHz, and as the frequency gradually increases, the loss reduction is further expanded.
The extremely low water absorption rate of LCP material is destined to become the core membrane material for 5G antenna transmission. Compared with PI, in addition to the lower dielectric loss factor Df of LCP, another important indicator is that its water absorption rate is extremely low, that is, it hardly absorbs moisture. Therefore, the loss-frequency curve of its substrate migrates before and after moisture absorption. Not obvious. On the contrary, the loss-frequency curve of PI substrate migrates more obviously before and after moisture absorption, and the transmission loss is larger.
Modified PI (ie MPI) has the ability to compete with LCP in the Sub-6G frequency band
From the performance point of view, the overall performance of MPI in the Sub-6G stage does not lose to LCP, and the supply can be converted by the original PI manufacturer. The full name of Modified PI (MPI) is Modified PI, which is prepared by introducing fluorine atoms and siloxane. The dielectric constant and dielectric loss factor of MPI are better than PI and close to LCP. The water absorption rate is also much better than PI, but it is still not as good as LCP.According to Taiwan Taimide data, in the Sub-6G frequency band, the difference in transmission loss between MPI material and LCP material is not obvious, and the performance of MPI in the 6-15GHz frequency band is only slightly lower than LCP, which can meet the requirements of antenna transmission in the 5G era. However, in the higher frequency bands above 15GHz, the gap between MPI materials and LCP materials is gradually obvious and widening.
It should be noted that the loss curve of Taimide's MPI product LKA-025 in the 25-30GHz frequency band is almost the same as that of LCP, but the extremely low water absorption rate of LCP is destined to be unable to replace LCP as a circuit board base for antenna in the millimeter wave stage.
The global LCP film market for 5G antennas can reach 23.3 billion yuan in the long-term
In practical applications, Apple’s newly released iPhone X at the end of 2017 applied LCP materials to the antenna for the first time, aiming to improve the antenna’s high-frequency and high-speed performance while reducing space occupation. According to industry teardown reports by electronics enthusiasts, iPhone X uses two sets of LCP antennas, an upper antenna and a lower antenna. In addition, the upper and lower antennas still use one set of PI antennas. There are two sets of LCP and PI antennas in the entire mobile phone.In 2018, iPhone XS/XS Max/XR has 3/3/2 sets of LCP antennas, but in the new machine series in 2019, because the series still does not support 5G and is subject to cost and supplier factors, it reduces The number of LCP antennas, use MPI antennas instead. Apple’s move made the market believe that under the Sub-6G band, MPI is a replacement material for LCP before transitioning to the 5G millimeter wave band because of its more suppliers, availability and better economy.
But in the long run, as 5G commercialization gradually matures and enters the millimeter wave frequency band, the production capacity and yield bottlenecks of superimposed LCP materials are broken and the material cost is further reduced. LCP will eventually be the ultimate destination of 5G antenna materials.
Calculation of LCP film usage for stand-alone antenna: Taking iPhone X as an example, according to Iparts Expert data, the size of the lower antenna is 9cm*7cm, and the size of the upper antenna is 6cm*4cm. Then the double-layer FPC required for the stand-alone The total area of LCP film consumables is 174cm2. With the double-layer board structure single-layer LCP film thickness of 25 μm and the LCP material density of 1.61g/cm3 (taken from a certain model of Polyplastics), the volume of the LCP film for the antenna used in a single machine is 0.435cm3 and the mass is 0.7g.
The price of LCP film for antennas: The LCP film for antennas is currently mainly supplied by Murata exclusively but mainly for personal use. Caitong Securities believes that its price is not very informative for the future situation after heavy volume (resin manufacturers break the film Barriers to entry, improved technology to increase yield, etc.). According to industry research, the current price of LCP film is distributed between 300-1600 yuan/square meter by grade, and the price selected for space calculation is 300 yuan/square meter, which is mainly based on the increase in productivity and yield bottlenecks in the future to drive penetration and the number of suppliers. The assumption that the increase causes the price to gradually fall.The LCP film market space for antennas is expected to reach 23.3 billion: According to Counterpoint data, the total global smartphone shipments in 2019 were 1.486 billion units. Based on this calculation, when the LCP antenna penetration rate reaches 100%, if the 6 antennas of each mobile phone are all LCP antennas, the long-term LCP film market space for antennas can reach 23.3 billion yuan; in addition, the film level is calculated The long-term resin space is 940 million yuan.