Thick Film Circuit Flexible, Easy Process
A thin film process such as screen printing and sintering is used to fabricate a passive network on the same substrate, and a separate semiconductor device chip or a monolithic integrated circuit or a micro component is assembled thereon, and then a hybrid integrated circuit is packaged. Thick Film Circuit hybrid integrated circuit is a micro-electronic functional components.
1. Features and applications
Compared with thin film hybrid integrated circuits, Thick Film Circuit hybrid integrated circuit is characterized by a more flexible design, simple process, low cost, especially suitable for multi-species small batch production. In electrical performance, it can withstand higher voltages, greater power and larger current. Thick Film Circuit microwave integrated circuit operating frequency can reach more than 4 GHz. It is suitable for a variety of circuits, especially for consumer and industrial electronic products with analog circuits. The substrate with Thick Film Circuit network has been widely used as a micro-printed circuit board.
2. The main process
According to the circuit diagram first divided into a number of functional components, and then use the plane layout method into a substrate on the plane circuit layout, and then use the photographic plate method to produce screen printing Thick Film Circuit network template. Thick Film Circuit hybrid integrated circuit The most commonly used substrate is the content of 96% and 85% of the alumina ceramic; when the requirements of thermal conductivity is particularly good, the use of beryllium oxide ceramic. The minimum thickness of the substrate is 0.25 mm and the most economical size is 35 x 35 to 50 x 50 mm. The main process for making Thick Film Circuit networks on substrates is printing, sintering and twisting. Commonly used printing method is screen printing.
Screen printing process is the first screen fixed in the printing press frame, and then stencils on the screen; or in the screen coated with photoresist, directly in the above manufacturing template, and then put the substrate under the net, the thickness The membrane slurry is poured onto the screen, pressing the slurry into the mesh with a scraper, and printing on the substrate to form the desired Thick Film Circuit pattern. Commonly used wire mesh with stainless steel mesh and nylon mesh, sometimes with polytetrafluoroethylene mesh.
During the sintering process, the organic binder is completely decomposed and volatilized, solid powder melts, decomposes and combines to form a dense, Thick Film Circuit. The quality and performance of the Thick Film Circuit are closely related to the sintering process and the ambient atmosphere, and the heating rate should be slow to ensure that the organic matter is completely removed before the glass flows. The sintering time and peak temperature depend on the slurry and film structure used. To prevent Thick Film Circuit cracking, but also to control the cooling rate. Commonly used sintering furnace is tunnel kiln.
In order to achieve the best performance of the Thick Film Circuit network, the resistance should be burned after firing. Commonly used methods are sandblasting, laser and voltage pulse adjustment.
3. Thick Film Circuit material
Thick Film Circuit refers to the substrate with the printing sintering technology formed by the thickness of several microns to tens of microns of the film. The material for making such a film is called a Thick Film Circuit material.
Thick Film Circuit material is a kind of coating or slurry, by one or several solid particles (0.2 to 10 microns) evenly suspended in the carrier and the formation. In order to facilitate the printing process, the slurry must have a suitable viscosity and thixotropy (viscosity with the external force to change the nature of). Solid particles are part of the Thick Film Circuit that determines the nature and use of the membrane. The carrier undergoes decomposition during the sintering process. The carrier contains at least three components, a resin or a polymeric binder, a solvent and a surfactant. The binder provides a basic rheological property to the slurry; the solvent dilutes the resin and then volatilizes to dry the print pattern; the activator allows the solid particles to be impregnated with the carrier and suitably dispersed in the carrier.
According to the nature and use of Thick Film Circuit, there are five types of pulp used: conductor, resistance, medium, insulation and encapsulation of the slurry.
The conductor paste is used to make thick-film conductors, forming interconnects, multilayer wiring, microstrip lines, solder lands, Thick Film Circuit resistors, Thick Film Circuit capacitor plates, and low resistance in Thick Film Circuit circuits. The welding area is used to weld or paste discrete components, devices and outer leads, and is sometimes used to weld metal covers to achieve encapsulation of individual substrates. Thick Film Circuit conductor uses different, there is no one slurry to meet all these requirements, so use a variety of conductive paste. The common requirement for conductor paste is conductivity, adhesion, anti-aging, low cost, easy welding. The metal components used in the commonly used conductor paste are gold or gold-platinum, palladium-gold, palladium-silver, platinum-silver and palladium-copper-silver.
In the Thick Film Circuit conductor paste, in addition to the appropriate size of the metal powder or metal organic compounds, there are appropriate size and shape of glass powder or metal oxide, and suspended solids particles of organic vehicles. The glass can bond the metal powder firmly to the substrate to form a Thick Film Circuit conductor. Commonly used alkali-free glass, such as borosilicate lead glass.