PCB News - Development Trends of Foreign pcb Manufacturing Technology

Development Trends of Foreign Printed Circuit Board Manufacturing Technology

With the development of micro device manufacturing and surface mounting technology, the innovation and improvement of the manufacturing technology of printed boards are promoted faster, especially the wire width of the circuit pattern. At present, it is widely used in foreign countries to pass three wires between the pins to achieve practicality. The wire width of the stage is that 4-5 wires pass between the pins, and it develops toward a thinner wire width. In order to adapt to the narrower spacing of SMD multi-leads, the printed circuit board wiring is thinned. The processes that are being popularized are: CAD/CAM systems are generally used, and the data provided from the design is converted into production materials through the manufacturing system; thin copper foil and thin dry film photoresist are used in raw materials; printed circuits are required due to narrow spacing The surface of the board has a smooth and flat copper surface in order to make micro-pads and circuit patterns with fine lines and narrow spacing; the substrate used should have a high thermal shock ability, so that the printed circuit board can be used in electrical equipment. The process will not produce defects such as bubbles, delamination and pad bulging after many times, ensuring the high reliability of surface mount components; and using high-viscosity copper foil and modified epoxy resin to ensure that it is adequate at the soldering temperature It should have high bonding strength and high dimensional stability to ensure the consistency and accuracy of the fine circuit pattern positioning during the production process. In a word, the development speed of the manufacturing technology of thin-wire and narrow-pitch printed circuit boards is very fast. If you want to keep up with the world's advanced technology, you must understand the current development trends in this area abroad.

2. Development Trends of Key Process Technologies Abroad

1. Negative film production and graphics transfer process

The quality of film production and graphics transfer directly affects the quality of making fine circuit graphics. Therefore, computer-aided design systems (CAD) are commonly used in the production of negatives to design circuits and interface with computer-aided manufacturing (CAM) to produce high-precision, high-resolution light-painting negatives through data conversion. Due to the high wire density, the wire width and spacing are 0.10-0.05mm, in order to ensure the accuracy and accuracy of the negative wire pattern, and the image quality of the circuit pattern, the cleanliness of the working room is required to be high, usually using 10,000 or 1,000 to ensure The high quality of film imaging.

In the aspect of pattern transfer process, the material used for imaging is thin photoresist with high resolution, and liquid photoresist is used for CD (electrophoresis) and solder resist. Among them, the photoresist layer coated by electrophoresis has a thickness of 5-30 microns, which is controllable, and its resolution can reach 0.05-0.03mm. It has played a great role in improving the accuracy and consistency of fine circuit patterns and solder mask patterns.

In the process of circuit pattern transfer, in addition to strictly controlling the process parameters, the cleanliness of the workshop is also very high, reaching the standard of 10,000 or less. In order to ensure the high quality of graphics transfer, indoor working conditions must be ensured, such as controlling the indoor temperature at 21±1 degree Celsius and relative humidity at 55-60%. 100% of the produced negatives and semi-finished products for image transfer imaging must be inspected.

2. Drilling technology

Drilling quality must first ensure the high reliability and high quality of plated through holes, and the drilling quality must be strictly controlled. In this regard, both at home and abroad have attached great importance. In particular, the thickness and aperture of the surface-encapsulated multilayer printed circuit board are relatively high, so the quality of the plated through holes has become the key to improving the pass rate of the surface-encapsulated printed circuit board. At present, the diameter of through hole is 0.25-0.30mm in foreign countries. The key to the small diameter of through holes is the development and use of high-precision, high-stability CNC drilling machines. In recent years, CNC drilling machines and special tools capable of drilling holes with a diameter of 0.10 mm have been developed and used abroad. In terms of drilling, experience tells us that it is very important to correctly select the drilling process parameters on the basis of studying the physical and chemical properties of the substrate. At the same time, it is necessary to correctly select the auxiliary materials used and the corresponding tools and fixtures (such as: upper and lower backing plates, positioning methods, drill bits, etc.). In order to adapt to the micro-aperture, laser drilling technology is also used.

3. Hole metallization technology

In terms of hole metallization technology, in order to ensure the high reliability of the hole metallization quality, the pretreatment after drilling adopts a new type of etchback and decontamination process, that is, the low-alkaline potassium permanganate method, which provides excellent The surface of the hole wall eliminates wedge grooves and crack defects. It also adopts advanced direct electroplating process, vacuum metallization process and other process methods to meet the metallization needs of small holes, micro vias, blind vias and buried vias of various types of printed circuit boards.

4. Vacuum lamination process

Especially for the manufacture of multi-layer printed circuit boards, vacuum multi-layer presses are generally used abroad. This is due to the characteristic impedance (Z0) requirement for the internal pattern of the surface-mounted multilayer printed circuit board. Because the characteristic impedance is related to the thickness of the dielectric layer and the width of the wire (see the following formula):

Z0=60/ε.LN.4H/D0 Note: ε is the dielectric constant of the material

H dielectric material thickness

D0 is the actual width of the wire

The dielectric constant and the actual width of the wire are known, so the thickness of the dielectric material becomes the key factor of the characteristic impedance. Using vacuum lamination equipment and computer control, the lamination quality has been significantly improved. Because the layers of the multilayer printed circuit board have been evacuated before vacuum lamination to remove low-molecular volatiles, the lamination pressure is extremely reduced, which is only the conventional multilayer printed circuit board lamination pressure. /4-1/2, so that the thickness of the dielectric material between the conductor pattern layers of the multilayer printed circuit board is uniform, the accuracy is high, and the tolerance is small, and the technical index of the characteristic impedance Z0 is within the range of the design requirements. At the same time, the vacuum lamination process is used to improve the surface flatness of the multilayer printed circuit board and reduce the quality defects of the multilayer printed circuit board(such as lack of glue, delamination, white spots and dislocation, etc.).

Three, testing technology is an important means to ensure the implementation of the process

According to the development of Denso technology from pin-insertion technology to surface packaging technology (bare chip direct mounting technology and fine pitch technology)-multi-chip module (MCM) technology or multi-chip packaging technology, it enables multi-layer printed circuit board circuit pattern detection more difficult. For this reason, high-precision, high-stability testing equipment is being developed and used at home and abroad. At present, there are two types of testing equipment: non-contact and contact.

1. Non-contact detection technology

detection technology is an important means to provide physical and chemical performance data of printed circuit boards. With the changes in the accuracy and density of printed graphics, the use of artificial vision methods for a long period of time has not been adapted to the high-speed development of high-tech needs. The detection technology and equipment have been developed rapidly, and the use of functions has gradually replaced artificial Visual inspection is used to judge product quality. It moves from the appearance inspection of the circuit pattern to the inspection of the inner circuit pattern, thus pushing the pure inspection to the direction of combining quality monitoring between processes and defect repair. Its main characteristics are: the use and application of computer software and hardware technology, high-speed image processing and pattern recognition technology, high-speed processing hardware, automatic control, precision machinery and optical technology, it is the product of a comprehensive variety of high-tech. There is no contact, no damage, no damage to the detection parts, and it can detect the places that cannot be detected by contact. Among them, there are the following types of equipment:

Bare board appearance inspection technology and equipment is AOI (Optical Tester). Mainly adopt the design specification inspection method to test two-dimensional digital graphics. With the emergence of surface mounting technology and three-dimensional molded printed circuit boards, the design specification inspection method will have completely different connotations. It can not only detect the width of the wire and the line spacing, but also the height of the wire. Therefore, the existence of a three-dimensional layout inevitably requires more advanced sensors and imaging technologies. Non-contact AOI testing technology is a product that integrates X-ray, infrared technology, and other testing technologies.

X-ray inner layer fluoroscopy detection technology

The X-ray used in the early days has a focal length of 300μm, and its detection accuracy can only reach 0.05mm. At present, the focal length has reached the micron level, and it has been able to measure with an accuracy of 10 microns. Used in conjunction with image processing, it can perform high-resolution see-through and inspection of the inner circuit pattern of the multilayer printed circuit board.

2. Contact detection technology and equipment

The testing method of printed circuit board mainly adopts online tester, also known as static function test. There are many models at present, and advanced equipment can quickly deal with quality defects (including open circuits and short circuits) caused by errors in the manufacturing process. There are universal continuity testers, special continuity testers and flying probe mobile continuity testers. The latter is suitable for electrical performance testing of small batches of high-density, high-precision double-sided and multilayer printed circuit boards.