Thick Film Integrated Circuit Widely Used
Thick film integrated circuit screen printing process
Thick film technology and thin film technology is an important technology in electronic packaging, thick film technology using screen printing and sintering methods, thin film technology using coating lithography, physical deposition and other methods. The main features of the thin film circuit are: manufacturing precision is relatively high, can achieve small hole metallization, can be easily used to manufacture multi-layer dielectric circuit, thick film circuit is the development of small electronic product development is relatively wide and small size is very large The development potential. With the development of technology, thick film hybrid integrated circuits use a growing scope, and gradually penetrate in various fields.
Overview of Thin Thickness Integrated Circuits
Thin integrated circuits can be roughly divided into two categories: semiconductor integrated circuits and hybrid integrated circuits, and hybrid integrated circuits can be divided into two kinds, one is the thin film hybrid integrated circuit, which is the application of vacuum spray thin film technology manufacturing. The other is a thick film integrated circuit, is the application of screen printing thick film manufacturing technology. The so-called film is about 1μm film thickness, thick film is 10 ~ 25μm film thickness, whether it is film or thick film has its own advantages.
2 thick film integrated circuit screen printing process
2.1 ceramic plate
The use of 90% ~ 96% alumina ceramic substrate, is a kind of alumina (Al2O3) as the main material, has good conductivity, mechanical strength and high temperature resistance. When making thick film should pay attention to the ceramic plate material, size, roughness, warping and surface defects and pollution, and in the purification between the ultrasonic cleaning.
There are 3 kinds of conductor slurry, resistive slurry and insulating paste. The slurry is usually composed of precious metal and low melting glass. When preparing the slurry, pay attention to the material, viscosity and expansion coefficient of the slurry. Printing thick film circuit used by the slurry, the composition of gold, silver, platinum, palladium and so on. The above metal powder is dispersed in an organic resin binder into a paste, and then printed on a ceramic substrate by screen printing. By burning at high temperature, the organic resin binder is burned off, and almost all of them are pure precious metals, which are adhered to the substrate due to the vitreous effect. This film can be used as thick film lines, thick film resistors, thick film capacitors and semiconductor integrated circuit with the underlying metal sheet.
(1) with silver as a conductive material its resistance is very low, so sometimes also use silver - palladium, silver mixture as a conductive material.
(2) In order to form a resistive film on the substrate, the resistive material used is mainly silver, gold and palladium.
(3) The electric conductor, the electrode, etc. of the small-sized capacitor are manufactured by the overlapping printing method. The electrode material is composed of platinum - gold, palladium - gold and silver.
2.3 Screen printing plate production
(1) network box: printing thick film circuit of the screen frame using aluminum and aluminum alloy, frame specifications are generally 100mm × 150mm and 150mm × 200mm. The frame shape is usually rectangular.
(2) screen: printing thick film circuit using stainless steel wire mesh or nylon mesh. General circuit printing 200 ~ 300 mesh screen; multi-layer wiring or require more precision, you can use more than 300 mesh screen.
(3) Photosensitive adhesive: Due to the thick film circuit silk screen requires a thick ink film (slurry film), so the use of the film can be applied to 20 ~ 30μm thick photoresist, but after the development of edge defects shall not occur.
2.4 thick film silk screen
The screen printing image of the integrated circuit is miniature, requiring high printing accuracy, so the printing press, printing plate, substrate (substrate), ink and so on need high precision, printing place must also keep the temperature, and remove the dust.
Scraper material is generally polyurethane rubber or fluorinated rubber, hardness Shore A70 ° ~ A80 °. In addition, the choice of the shape and hardness of the scraper, you should consider what kind of pattern on the circuit board to print. Under normal circumstances, the blade edge of 90 ° or 60 °, scraper angle of 70 ° ~ 75 ° thick film printed circuit board printing machine has semi-automatic and automatic two categories. Semi-automatic screen printing machine only the substrate is completed by hand, and other processes automatically completed, such as the Ministry of Information Industry Electronics Research Institute developed the WY-155, WY-203-type precision screen printing press, with printing accuracy Less than 0.01mm, scraper pressure and printing speed can be adjusted, vacuum table x, y, θ three-dimensional precision adjustment, the whole PLC control, the indicators are met or exceeded the level of similar foreign equipment, is the domestic thick film integrated circuit The preferred equipment for the manufacturer.
2.5 thick film circuit after finishing
General printing thick film circuit board, the first conductor printing, and then repeated printing resistance of 2 to 3 times, sometimes according to the situation may be appropriate cross-glass coating printing, after printing the following processing or processing.
(1) leveling process: after printing the printed matter placed 5 ~ 7min until the disappearance of moire.
(2) Drying treatment: Drying is carried out at a temperature of about 100 ° C.
(3) firing: firing at a temperature of about 650 to 670 ° C. This process is very important, so at any time to adjust the furnace temperature, to keep the temperature suitable for slurry sintering.
(4) adjustment: adjust the resistance value, the general use of sandblasting to the circuit board or laser adjustment resistor method to adjust.
(5) Enclosure: protects the made inserts.
2.6 thick film resistors silk screen production process
Thick film printing is similar to the general screen printing, but thick film printing products are thick film resistors, capacitors and other circuit components. Thick film resistor accuracy, electrical stability and solderability and other technical indicators, and thick film quality of silk screen, the thickness of the ink film has a small change, the product can not be used. Therefore, the thick film thickness uniformity of the film will directly affect the product yield. Ordinary thick film resistor is a thickness of about 20μm cube, if the control of its thickness is certain, you can use the ratio of the length and width to determine the resistance of the resistor. The aspect ratio of the thick film resistor is up to 10: 1 to the minimum of 1:10. For the printing ink (resistive slurry) with the same resistance value, the surface resistance can only vary from 10 to 1/10. In order to obtain resistance values other than this range, it is necessary to use a slurry with a different resistance value.
2.7 Screen printing defects on the thick film circuit
In the production of thick film printed circuit, silk screen defects on the quality of the finished product is relatively large.