PCB technology in the new century

Release Time:

2013-04-18 00:00

In the past two years, the development of printed board technology is so fast that many experts predict that our industry will soon enter the microvia-dominated HDI era in the year 2000.

HDI stands for High Density Interconecting, meaning "high density Interconecting," which was put forward by the United States in 1997. Earlier Japanese custom called "Build-up Multilayer" (BUM for short) has the same meaning.

According to IPC data, the significance of HDI is (1) aperture ≤0.15mm(6mil); (2) hole ring ≤0.25mm (10mil); (3) connecting points (connecting) density ≥130 points/square inch; (4) Wiring density ≥117 inches/square inch. For HDI printed boards, the line width/spacing is less than 0.075mm(3mil).

The microthrough hole of HDI printed board is not made by the usual CNC drilling machine, and there are four kinds of hole forming methods; Laser drilling (burning) holes; Photolithogenesis; Discussion on plasma Etching and alkali Etching. Since 1999, the most popular method has been to use lasers to drill micro-through holes to make laminated multilayer printed boards.

The main market for HDI printed boards comes from mobile phones. According to analysis, 25 million mobile phones will be produced every month in the world after 2000, and China is the largest market. The world's largest mobile phone companies Nokia, Ericsson and MOTOROLA, as well as Siemens and NEC, all buy mobile phone boards from China, especially printed ones with embedded blind holes. In addition, the era of foreign brands in China's mobile phone market is over. Approved by the State Planning Commission, there are nine designated factories that can produce mobile phones, including Kejian, Xahua, Konka, Haier, TCL, ZTE and so on. They are determined to get a piece of the pie from the tiger. Konka is one of the manufacturers with the highest enthusiasm and expectation for the mobile phone market. Within three years, Konka will invest 500 million yuan to achieve an annual output of 2 to 3 million units, accounting for 20% of the market share within five years. A large number of high-density interconnected multilayer boards required by Konka mobile phones must be purchased from domestic printing board factories. In addition to mobile phones, video cameras, anti-theft monitoring systems, high-precision instruments, flat computers, etc., will use the HDI multilayer board.

According to the famous NT Information company assessment, the HDI microplate market in the world in 1997 was 647 million dollars, in 1999 doubled to 1.94 billion dollars, Japan production is the largest, China mainland, Taiwan Province of China, the United States and Europe are the main producers of HDI microplates in the world.

Three years ago, no one in China could mass produce printed boards for mobile phones. At that time, mobile phones were made in foreign countries and PCB on mobile phones were all made in foreign countries. The first domestic mobile phones were produced in early 1998. Up to now, there have been many PCB factories in China that can mass produce high-difficulty mobile phone boards, including Shanghai Meiwei, Zhuhai Multilayer, Huizhou Huafeng, Dongguan Maotai, Kunshan Hushi, Zhuhai Chaoyi. The monthly production of embedded/blind hole chemical impregnated gold mobile phone boards is 20,000-30,000 square meters, for the world's largest mobile phone factories for assembly. After more than two years of hard work, Zhuhai multilayer can ship thousands, tens of thousands of mobile phone board every day, the main customer is MOTOROLA. Only two years into production, Shanghai Meiwei, in the mass production of buried blind hole mobile phone plate, jumped to become the industry technology "big brother".

A batch of domestic circuit board factory development of buried/blind hole mobile phone plate has completed the template, into the order batch production stage, such as health Yi electronics, Tianjin Prinlin, Shenzhen Shennan, Zhuhai Deli, Yili anda, Tim Li, Shantou ultrasonic, Dongguan Ya Xin and other companies.

All signs show that the year 2000, for the printed board industry, the era of HDI high density interconnection has arrived.

Laser drilling machine

Laser drilling machine is indispensable to HDI technology. 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, but it soared to 7.5 million in 1999, and is estimated to be 1500 in 2000 and 2200 in 2001.

According to the introduction of Professor Belongsheng in Shenzhen in November 1999, as of November 1999, 14 companies in Taiwan Province have purchased a total of 47-49 laser drilling machines, and 8 companies in mainland China have purchased laser drilling machines: Zhuhai Chaoyi, Zhuhai Deli, Zhuhai Multilayer, Shanghai Meiwei, Kunshan Hushi, Huizhou Huatong, Shantou Ultrasonic, 1-3 each, a total of 16. It is said that Huatong and Chaoyi are currently the largest buyers of laser drilling across the Taiwan Strait, each will buy 15-20 units. Laser drilling machine is divided into two types, CO2 and YAG, each has its own characteristics.

Electroplating and electroless nickel/gold plating

Selective plating dumb (sand) gold technology

In the traditional printed board process, the surface is coated with lead tin alloy, that is, hot air smoothing, Cantonese called tin spray, many printed board factories only this process. As the printed board tends to become thinner, denser, smaller and lighter, hot air leveling for many new varieties of printed board has been unable to adapt, in a large number of reduction, and electroplating nickel/gold, electroless nickel/gold leaching more and more. In the Pearl River Delta, many PCB factories are almost all the production of nickel/gold plate, a number of factories nickel/gold plate ratio is larger than hot air flat plate, some factories monthly production of 30,000 to 40,000 square meters, double and multilayer board is almost all nickel/gold plate or more than 50%. In order to meet the requirements of different customers, some PCB factories have configured a number of different purposes of the gold cylinder. Soft gold cylinder for welding (24K gold), nickel is usually plated 2.5-3.0um, gold 0.05-0.075um, Cantonese called water gold plating; Printed boards also require nickel layer 5um, gold layer 0.1um above. On the printed board, the parts that play the role of buttons, wear resistance and insertion need to be plated with hard gold, or selective local gold plating. The plating thickness is required to be 0.5,1.0,2.0um. Both thin gold plating and selective local thick gold plating are used in a PCB. In the process of many factories have been mature, become the factory's patent technology. Electroless nickel plating/gold immersion automatic line has been developed greatly in Guangdong, and about 20 professional PCB factories have established such automatic production line.

In the past two years, some customers require dumb gold plating, some people say as gold. That is to say, the color of gold is not bright, so that electronic factory assembly is not dazzling, European and American factories spread over. At present, there are some factories in Guangdong specially equipped with matte copper plating, matte gold solution formula, to suit the needs of customers.

Into the 21st century, with the arrival of the HDI era, plating or dipping nickel/gold will certainly be more and more, a large number of mobile phone plate, mostly chemical nickel/gold, local thick gold plating, it is understood that the domestic development of chemical nickel/gold solution, Shenzhen Ike company's series of products have been subjected to batch automatic line production assessment, Its prospect is certainly bright, its quality with imported liquid phase when.

It should also be noted that, in addition to chemical nickel/gold, one of the newer processes, chemical silver leaching, is on the way,

Macoemid,Alphametal and other companies are already testing silver immersion in some big factories in Guangdong province.

Through hole plug hole

Electronic assembly plants require the number of perforated holes of printed boards has an increasing trend, many high density multilayer boards, BGA (ball grid display package) multilayer boards of 0.2-0.3mm perforated holes are required to plug holes, customers require 95% of the microholes to plug with solder resistance ink, if the hole leakage will be returned or fined. The intention of the through hole plug hole has three: one is to prevent tin from passing through the through hole to the surface of the element caused by short circuit during wave soldering; Second, to avoid the flux remaining in the pass-through hole after installation; Third, the surface of the electronic factory after the installation of the circuit board, in the test surface requires the vacuum can form a negative pressure can be detected. It is one of the important indicators of whether a PCB factory can receive orders of high density and high difficulty printed board. A high-density BGA or buried/blind hole printed board, often thousands of through holes, small aperture, pad is small, slightly inaccurate, may plug dislocation. Plug hole technology is very learned, plug is not correct, plug discontent, plug hole drying and curing after blasting, plug hole is still leaking light, there are many problems, plug hole is not an easy thing.

The core panels of the laminated multilayer (BUM) are also plugged after drilling, PTH, and electroplating. At present, the manufacturers of mobile phone buried/blind hole plate are exploring the different process skills of the hole. There are several types of plug materials: solder resistance ink, epoxy resin, conductive adhesive (e.g., silver - copper - epoxy paste). Factories are maturing in methods, experience and skills, but are reluctant to disclose their secrets. In general, plugging through holes is one of the key technologies to make BUM laminate.

Horizontal automatic line

In recent years, many domestic PCB factories have introduced a lot of horizontal automatic line technology and equipment, such as horizontal direct plating line, horizontal heat resistance and oxidation prevention line, horizontal pulse surface plating line, horizontal hot air leveling line, horizontal black (brown) line, which greatly simplifies the whole process and improves the efficiency. Among these horizontal devices, the inner plate horizontal blackening line is popularized most rapidly. The traditional blackening process is vertical, the whole line is about 20 cylinders, the program blackening process is vertical, the whole line is about 20 cylinders, the program control impregnation, rise and fall, dripping time, vertical shelf, now good, a horizontal line, like brush machine, put the board on the machine, the conveyor belt is transmitted to the end, the board blackening is completed. It is understood that the Pearl River Delta region has at least more than ten horizontal blackening lines.

After the inner board is blackened horizontally, the remaining processes of the inner board can basically realize full automation, which is another trend of PCB technology development in recent years. A few years ago, the inner plate with liquid sensitive adhesive (also known as wet film) instead of dry film as imaging, there have been many successful examples in Guangdong, but all in the way of screen printing. At present, Hong Kong Lejian, Zhan Yi, Taiwan Foundation Xingye, Ciba, Buerkle and other companies can implement roller coating on both sides at the same time, and then conveyor belt drying, to achieve the inner plate with liquid sensitive adhesive to complete the whole process of the inner plate light imaging. After the inner plate is exposed, it enters the fully self-generated horizontal acid etching, film removal, and then transmits to the horizontal blackening line to form a complete automatic inner plate production line. In the 21st century, this system equipment will soon enter the multilayer board company, fully automated mass production of the inner board, and realize the era of unmanned operation will soon come. In Huizhou Huatong, the whole process of the inner plate has basically realized automation. The company uses automatic laminating machine instead of liquid sensitive adhesive double-sided roll coating system to realize the automation of basic unmanned operation. In the 21st century, the horizontal automatic line will continue to increase, the horizontal pulse plate copper plating technology will soon mature and promote. As the efficiency of horizontal automatic line is improved, the process capacity is accelerated, and the time is shortened, the competitiveness of factory orders will be strengthened.

Carbon conductive ink and strippable "blue glue"

Many customers place orders, after the completion of solder resistance, but also need to print a layer of carbon conductive ink on the circuit board, keyboard type, line graphics, and linear shape. Some orders have a simple laminated multilayer circuit board printed on both sides of a dual or four-layer board after welding and then printing a layer of conductive carbon graphics.

Modern printed board to go through many welding assembly process, in order to make the second or third time on the same board to welding part of the pad and component hole is not stained with solder, these holes and pad printed on a layer of strippable "blue glue" protection, the need for the part of the hole and pad welding will tear off the blue glue. Printing strippable "blue glue" is now a step on the printed board. "Blue glue" is a single component ink, do not need to dilute, with 10-20T screen printing, about 150℃ drying 20-30 minutes cure. "Blue glue" can withstand the thermal impact of 250-300℃ wave soldering, easy to be peeled off by hand, will not leave residual glue in the pad and hole.

Entering the new century, printed board factories should have the ability of silk screen carbon ink and strippable "blue glue" to adapt to the needs of electronic factory assembly, in order to survive and develop better.

Ultra-thin multilayer board manufacturing technology

Ultra-thin multilayer board first 3-4 years in Europe, the United States, Japan began to apply, is one of the very rapid development of printed board types. Initially a large number of applications in the expansion of the function of the computer board, called PCMCIA, later the use of this card rapidly expanded, PC card, IC card, network card, mouse board, etc. These board cards are all ultra-thin multilayer board, generally 4, 6, 8 layers, each layer 0.1mm, aperture 0.2-0.3mm; Double-sided SMT, the total thickness of 4 layers is 0.4mm; 6 layers 0.6mm. Many new high-tech electronic products in recent years are used in ultra-thin multilayer printed boards. The core of this kind of board is "thin", the core board 0.1mm, the production process of brush plate, electroplating, blackening, etching, laminating, testing, etc., each process should have a way to deal with the chip "thin" and brought about by the problem. Usually, the linear width/spacing of the plate is 5±1mil(0.10-0.15mm), only one semi-cured sheet is placed between layers, and the warpage degree and thickness tolerance of the finished plate are required to be strict. The surface coating is usually plated or dipped Ni/Au. Now the ultra-thin multilayer plate has been mass produced in Guangdong, dozens or millions of pieces a month. With the progress of electronic information technology, ultra-thin multilayer board is predicted to be more and more in various electronic product fields.

Impedance technology (Impedance)

In the past few years, the wind has been blowing to the printed board requiring a characteristic impedance index. In the 21st century, the characteristic impedance multilayer board is no longer the wind but the rain. The transmission of communication high-frequency signals and the acceleration of computer computing speed will put forward more stringent requirements on the thickness, line width, spacing, line thickness, welding resistance and so on between multilayer plates. The requirements on the side erosion of the line and the verticality of the edge are more stringent. The gap, pinhole and sawtooth on the line will not be received by the current IPC standard of -20%. All of these more stringent indicators for printed boards are reflected in the characteristic impedance performance. Multinational electronics companies often threaten to control the characteristics of the impedance index of the factory, can get in order.

It is said that in recent 1-2 years, a number of domestic printed board factories have purchased the UK polar characteristic impedance tester, and carry out the research of characteristic impedance multilayer plate. Predicted in the 21st century, the high frequency impedance circuit board market is large, can make impedance multilayer board, it shows that the multilayer board factory process, detection, management of all aspects of the level has risen a grade. Admittedly, the production characteristic impedance plate also poses new challenges to the upstream materials such as copper clad plate, copper foil and semi-cured sheet (such as dielectric constant, high Tg, 9 micron copper foil clad plate, etc.).

Laser direct imaging

Traditional inner and outer optical imaging requires the use of silver salt or diazo (phototool), because a gap on the negative, pinhole or a dust on the exposure frame will cause batch repeated defects in the printed board, especially in the production of 0.05-0.075mm line width/pitch PCB. In addition, the film is often subjected to temperature and humidity changes and elongation and shortening interference, large plate size of the film is difficult to alignment. Laser Direct Imaging (LDI) was developed to solve the problem caused by negative film. This method directly uses the output data of CAM workstation to drive the UV laser imaging device to scan at high speed on the surface of the plate with the photosensitive dry film, thus completing the task of the traditional photoimaging negative exposure, similar to a laser plotter, thus eliminating the task of the negative exposure, similar to a laser plotter, thus eliminating the negative development machine. Diazo film developer, copy machine, light drawing machine and a lot of other machines, also omit diazo film and silver salt film, admittedly repair negative, negative inspection machine has also been eliminated. This method can rapidly mass produce 0.05mm line width/spacing circuit boards, greatly save the investment and cost, shorten the process, improve the quality of circuit boards, can be said to be a revolution in the printing board industry imaging. Laser direct imaging in the United States, Japan a number of companies developed, Dupont company developed medium materials and Orbot and other companies of laser equipment since 1998, in the United States, France, Canada, Austria and other countries trial, reflect very good. It is predicted that this laser direct imaging equipment and method will be introduced into China in the early 21st century.

Face reality and step into the 21st century

In summary, in the 21st century, the printed board industry will enter the era of microvia-dominated high density interconnection (HDI). The printed board will become thinner and denser, and the quality requirements will become more and more strict, requiring buried/blind holes, impedance characteristics, chemical nickel/gold. Local thick plating technology to meet the mobile phone (mobile phone), digital television, flat computer and many other high-tech products on the printed board requirements. The enterprises continue to study and develop the vitality of the printed board mass production technology, can catch up with the pace of The Times, can receive a large number of high value-added orders.

However, in fact, at this stage, to each printed board factory turn a circle can be found, in addition to very few PCB factories, the current factory production of boards, accounting for 80-90% of the line width of 5-8mil(0.13-0.20mm), aperture of 0.3mm above, most factories rely on this kind of board profit and accumulation. On the other hand, the current laser drilling machine is fashionable enough, but the laser machine also has limitations, it only deals with plate thickness <0.4mm, aperture <0.2mm hole, a little thicker plate and a little bigger hole, but also rely on ordinary CNC drilling machine to achieve. And in real life, it is impossible for every printed board factory to make mobile phone boards, and it is impossible for every factory to have all the latest technology. Therefore, it is advocated to face the reality, for the survival and development of the enterprise, to develop a few of the new mass production technology should be, must form the characteristics of the enterprise technology and products, so as to maintain a dominant position in the market competition.

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