Entering the new century PCB technology

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In the past two years, the progress of printed board technology has been too fast. Many experts predict that in 2000, our industry will soon enter the HDI era dominated by Microvia.
In the past two years, the progress of printed board technology has been too fast. Many experts predict that in 2000, our industry will soon enter the HDI era dominated by Microvia.
HDI is the abbreviation of English High Density Interconecting, which means "high-density interconnection", which was proposed by Americans in 1997. The same as the earlier Japanese used to call "Build-up Multilayer" (BUM).
According to US IPC data, HDI contains (1) aperture ≤ 0.15mm (6mil); (2) hole ring ≤ 0.25mm (10mil); (3) connection density ≥ 130 points / square inch; (4) Wiring density ≥ 117 inches / square inch. HDI type printed board with line width/pitch ≤0.075mm (3mil).
The micro-vias of HDI printed boards are not made by the usual CNC drilling machine. There are 4 types of holes; laser drilling (burning) holes; photo-forming holes; plasma etching (Plasm Etching) and alkali etching holes. . Since 1999, the most popular is the use of laser drilling micro-vias to make laminated multi-layer printed boards.
The main market for HDI printed boards comes from mobile phone handsets. According to analysis, the world will produce 25 million mobile phones every month after 2000, and China is the largest market. Nokia, Ericsson, Motorola, and Siemens and NEC, the world's largest mobile phone companies, will purchase mobile phone boards in China, especially mobile phone printed boards with buried holes. In addition, China's mobile phone market is the end of the era of foreign brands. After the approval of the State Planning Commission, a total of nine fixed-point factories can produce mobile phones, including Kejian, Xoceco, Konka, Haier, TCL, ZTE, etc. They are determined to divide from the tiger's mouth. Have a piece of cake. Konka is one of the manufacturers with the highest enthusiasm and expectation in the mobile phone market. It will invest 500 million yuan in three years to achieve an annual output of 2 million to 3 million units, and account for 20% of the market share in five years. A large number of high-density interconnect boards required by Konka mobile phones Must be purchased at various domestic printing board factories. In addition to mobile phones, HDI multi-layer boards are used in cameras, anti-theft monitoring systems, high-precision instruments, and flat computers.
According to the evaluation of the famous NT information company, the HDI microplate market was 647 million US dollars in 1997, and it doubled to 1.94 billion US dollars in 1999. The largest output in Japan, the Chinese mainland, Taiwan Province of China and the United States and Europe are global HDI microplates. The main producing area.
Three years ago, there was no domestic printed board that could mass-produce mobile phones. When the mobile phone was a foreign product, the PCB on the mobile phone was all made in foreign countries. In the beginning of 1998, the Electronic Department of the Seventh Office produced the first batch of domestic mobile phones. Up to now, many PCB factories in China have been able to mass-produce difficult mobile phone boards, including Shanghai Meiwei, Zhuhai Multi-layer, Huizhou Huafeng, Dongguan Trade, Kunshan Hu Shi, Zhuhai Chaoyi, monthly production buried/blind The hole chemical immersion gold mobile phone board is 2-3 million square meters, which is used for assembling the world's largest mobile phone factories. After more than two years of hard work, Zhuhai multi-layer can ship thousands and tens of thousands of mobile phone boards every day. The main customer is MOTOROLA. Shanghai Meiwei, which has only been in production for two years, has become the “big brother” in the industry in mass production of buried blind mobile phone boards.
A number of domestic circuit board factories have completed the development of buried/blind hole mobile phone boards, and entered the batch production stage, such as Shengyi Electronics, Tianjin Pulin, Shenzhen Shennan, Zhuhai Deli, Yili Anda, Tianli, Shantou Ultrasound. , Dongguan Yaxin and other companies.
There are indications that in 2000, the era of HDI high-density interconnections has arrived for the printed board industry.
Laser drilling machine
HDI technology is inseparable from laser drilling machines. The formation of micropores is "burned" by a laser machine. In 1997, the total number of laser drilling machines in the world was only 240. In 1999, it surged to 7.5 million units. It is estimated to be 1,500 units in 2000 and 2,200 units in 2001.
According to Professor Bai Rongsheng introduced in Shenzhen in November 1999, as of November 1999, 14 companies in Taiwan have purchased 47-49 laser drilling machines, and 8 companies have purchased laser drilling machines in mainland China: Zhuhai Chao Yi, Zhuhai Deli, Zhuhai Multi-layer, Shanghai Meiwei, Kunshan Hu Shi, Huizhou Huatong, Shantou Ultrasound, each 1-3 units, a total of 16 units. It is said that Huatong and Chaoyi are the companies that purchase the most laser drilling holes on both sides of the Taiwan Strait, and each will add 15-20 units. Laser drilling machines are divided into two major types, CO2 and YAG, each with its own characteristics.
Electroplating and electroless nickel/immersion gold
Selective gold-plated matte (sand) gold process
In the traditional printed board process, the surface coating is a lead-tin alloy, that is, the hot air is leveled, which is called spray tin in Guangdong. Many printed board factories only have this process. As printed boards tend to become thinner, denser, smaller, and lighter, hot air leveling has become unsuitable for many new varieties of printed boards, which are greatly reduced, while electroplated nickel/gold, electroless nickel/dip More and more gold. In the Pearl River Delta, almost all PCB factories produce nickel/gold plates. The proportion of nickel/gold plates in a batch of factories is greater than that of hot air. Some factories produce 30,000-30,000 square meters per month. Almost all double and multi-layer boards are Nickel/gold plates account for more than 50%. In order to meet the requirements of different customers, some PCB factories are equipped with a number of gold cylinders for different purposes. Soft gold cylinder (24K gold) for welding purposes, nickel is usually plated 2.5-3.0um, gold 0.05-0.075um, Guangdong is called gold plating gold; printed board also requires nickel layer 5um, gold layer 0.1um or more. On the printed board, the buttons, wear-resistant, and plug-in parts need to be plated with hard gold, or selectively plated with gold. The plating thickness is required to be 0.5, 1.0, 2.0um, and the thin gold is also selected in a PCB. Partially plated with thick gold. Many factories have matured in the process route and become the patented technology of each factory. The electroless nickel/immersion gold automatic line has been developed in Guangdong, and about 20 professional PCB factories have established such automatic production lines.
In the past one or two years, some customers have requested dumb gold, and some people call it Shajin. That is to say, the color of gold is not required to be bright, so that the assembly of electronic factories is not dazzling, and the European and American factories have spread. At present, some factories in Guangdong have specially formulated solution solutions with matt copper and dummy gold to suit the needs of customers.
In the 21st century, with the advent of the HDI era, plating or immersion of nickel/gold will definitely increase. A large number of mobile phone boards are mostly chemical nickel/gold and partially plated with thick gold. It is understood that domestically developed chemical nickel / Gold solution, Shenzhen Aike's series of products have been subjected to batch automatic line production assessment, its prospects are certainly bright, and its quality is equivalent to imported liquid.
It is also worth mentioning that in addition to chemical nickel/gold, one of the newer processes, chemical immersion silver, is about to rise.
The immersion silver liquid of Macoemid, Alphametal and other companies has been promoted and applied in some large factories in Guangdong.
Via hole
Electronic assembly plants require an increasing number of vias for printed boards. Many high-density multilayer boards, BGA (ball grid display package) multilayer boards have 0.2-0.3mm vias. Requires plugging, the customer requires 95% of the micropores to be plugged with solder mask ink, if the via hole leaks, it will be returned or fined. There are three intentions for the via hole: one is to prevent the solder from penetrating through the via hole to the component surface during the wave soldering, and the second is to prevent the flux from remaining in the via hole after the component is not mounted; After the mounted circuit board, a negative pressure can be formed on the test surface to require a vacuum to perform height detection. The ability to have a via hole plugging technology is one of the important indicators for today's printed board factories to receive orders for high-density and difficult printed boards. A high-density BGA or buried/blind-hole printed board often has thousands of vias, a small aperture, and a small pad. If the alignment is not correct, it may be misplaced. The plug hole technique is quite learned. The plug is not correct, the plug is not full, the plug hole is dried and solidified, and the hole is still leaked after the plug hole. There are many problems. It is not easy to plug the hole.
The core of the laminated multi-layer board (BUM) is also plugged through the via holes formed after drilling, PTH, and plating. At present, manufacturers of mobile phone buried/blind hole plates are exploring the different craftsmanship techniques of the hole. There are several types of plug materials: solder resist inks, epoxy resins, conductive adhesives (eg silver-copper-epoxy paste). Process routes, experience and skills The factories are maturing, but they are not willing to disclose their plagiarism. In general, plugging the via holes is one of the key process technologies for making BUM laminates.
Horizontal automatic line
In recent years, many domestic PCB factory technical transformations have introduced a number of horizontal automatic line processes and equipment, such as horizontal direct plating lines, horizontal heat-resistant oxidation lines, horizontal pulse surface plating lines, horizontal hot air leveling lines, horizontal black (brown) The line has greatly simplified the whole process and greatly improved the efficiency. In these horizontal devices, the horizontal blackening line of the inner layer is promoted most rapidly. The traditional blackening process is vertical, with about 20 cylinders in the whole line. The program blackening process is vertical. There are about twenty cylinders in the whole line. The program controls the dipping, landing, dripping time, and the vertical shelf is off the shelf. Now, A horizontal line, like a brushing machine, puts the board on the machine, the conveyor is transported to the end, and the board is blackened. It is understood that there are at least ten horizontal blackening lines in the Pearl River Delta region.
After the blackening of the inner layer is horizontalized, the remaining processes of the inner layer board can be basically fully automated, which is another trend in the development of PCB technology in recent years. In the past few years, the inner layer plate used liquid photosensitive glue (also known as wet film) instead of dry film for imaging. There have been many successful examples in Guangdong, but they are all realized by screen printing. At present, Hong Kong Lejian, Zhanyi, Taiwan Foundation Industrial, Ciba, Buerkle and other companies can implement roller coating double-sided simultaneous gluing, and then conveyor belt drying, to achieve the inner layer with liquid photoresist to complete the inner layer The whole process of plate light imaging. After the inner layer is exposed, it enters the self-leveling horizontal acid etching and film removal, and then is transferred to the horizontal blackening line to form a complete inner layer automatic production line. In the 21st century, this kind of system equipment will soon enter the multi-layer board company, and the era of fully automated mass production of the inner board and the realization of unmanned operation will come soon. In Huizhou Huatong, the whole process of the inner layer board has been basically automated. The company uses the automatic film laminating machine to replace the liquid photosensitive adhesive double-sided roll coating system to realize the basic unmanned operation automation. In the 21st century, horizontal automatic lines will continue to increase, and horizontal pulse plate copper plating technology will soon mature and be popularized. As the horizontal automatic line efficiency increases, the process capability is accelerated, the time is shortened, and the competitiveness of the factory order is strengthened.
Carbon conductive ink and peelable "blue glue"
When many customers place an order, after completing the solder mask, they need to partially print a layer of carbon conductive ink on the circuit board. There are keyboard type, circuit graphics, and linear shape. Some orders are printed on a double- or four-layer board after solder masking, and a double-layer conductive carbon pattern is printed on both sides to form a simple laminated multi-layer circuit board.
Modern printed boards have to undergo multiple soldering and assembly processes. In order to make solder pads and component holes soldered on the same board for the second or third time, it is necessary to print these holes and pads. The strippable "blue glue" is protected, and the blue glue is peeled off when the hole and the pad are soldered. Printing the strippable "blue glue" is now also a step in the printed board. "Blue Glue" is a one-component ink that does not have to be diluted. It is screen printed with 10-20T and cured at about 150 ° C for 20-30 minutes. "Blue Glue" can withstand the thermal shock of wave soldering at 250-300 ° C and can be easily peeled off by hand without leaving residual glue in the pads and holes.
In the new century, the printing board factory must have the ability of screen printing carbon ink and strippable "blue glue" to meet the needs of electronic factory assembly in order to survive and develop better.
Ultra-thin multilayer board manufacturing technology
The application of ultra-thin multi-layer boards in Europe, the United States and Japan in the first 3-4 years is one of the types of printed boards that are developing very rapidly. Originally used in a large number of computer boards for expansion functions, it was called PCMCIA. Later, the use of such cards was rapidly expanded, such as PC cards, IC cards, network cards, and mouse boards. All the boards used are ultra-thin multi-layer boards, generally 4, 6, and 8 layers, each layer 0.1mm, aperture 0.2-0.3mm; double-sided SMT, 4-layer board total thickness 0.4mm; 6 layers 0.6mm . Many high-tech electronic products that have appeared in recent years have used ultra-thin multilayer printed boards. The core of this kind of board is “thin”, the core board is 0.1mm, the brushing board in the production process, electroplating, blackening, etching, lamination, testing, etc., each process must have a way to deal with the “thin” of the chip. The problem. Usually, the board width/pitch is 5±1 mil (0.10-0.15 mm), and the inter-layer prepreg is only placed one. The warpage and thickness tolerance of the finished board are very strict. The surface coating is usually plated or immersed in Ni/ Au. Ultra-thin multi-layer boards are now mass-produced in Guangdong, with dozens and millions of pieces per month. With the advancement of electronic information technology, ultra-thin multi-layer boards are expected to be more in various electronic products.
Characteristic Impedance Technology (Impedance)
In the past few years, the printed circuit board has been required to have the characteristic impedance index of the wind. In the 21st century, the characteristic impedance multilayer board is no longer windy but rainy. The transmission of high-frequency signals for communication, the speed of computer operation is accelerated, and the stricter requirements on the thickness, line width, spacing, line thickness, and solder resistance of the multilayer board are put forward, and the verticality of the line side etching and the edge is The requirements are even more demanding. The gaps, pinholes, and serrations on the line will not be received by the current IPC -20% standard. All of the more stringent indicators for the printed board are reflected in the characteristic impedance performance. Multinational electronics companies often threaten that factories that can control characteristic impedance indicators can get orders in volume.
It is said that in the past 1-2 years, a number of printed board manufacturers have purchased the British characteristic impedance tester and conducted research on characteristic impedance multilayer boards. It is predicted that in the 21st century, the market for high-frequency impedance circuit boards is large, and the production of impedance multilayer boards indicates that the level of process, inspection and management of this multi-layer board factory has risen to a new level. It is true that the production characteristic impedance board also poses new challenges to the upstream material copper clad laminate, copper foil and prepreg (such as dielectric constant, high Tg, 9 micron copper foil clad laminate, etc.)
Laser direct imaging
Traditional inner and outer photoimaging must use silver salt tablets or phototools. Due to a gap in the film, pinholes or a dust on the exposure frame, the printed board will be repeatedly duplicated. It is more prominent when making PCBs with a line width/pitch of 0.05-0.075mm. In addition, the film is often disturbed by the change of temperature and humidity and the elongation is shortened, and the film of the large plate size is more difficult to align. Direct Imaging LDI (Laser Direct Imaging) has emerged for the problems brought about by the film. The method directly utilizes the output of the CAM workstation