2 Industrialization of Photoetching Hole Method
There are many commercial processes for photoconductive vias, of which the SurfaceLam inarCircuits (SLC) launched by IBM in Yasu, Japan, in 1989 were the earliest harbingers. DuPont also introduced a dry film PID in July 1997. Its trade name is ViaLux100, which makes construction easier and media flatness better. IBM's Endicott plant in New York and the Austin plant in Texas have all changed the solvent image of SLC to aqueous solution visualization; the latter is called the motherboard of the ThinkPad laptop, and the workstation graphics card, PCMCIA card. The MCM-L and camcorders have over-produced circuit boards. In addition to the above-mentioned Probimer 52 or 65, there are still more than ten kinds of wet film or dry film type photosensitive media such as ShiplyFP-9500. The typical commercial process of photoetching etching is now summarized below.
2.1 SurfaceLaminarCircuits (SLC)
The core of the FR-4 double-sided panel is coated with an epoxy resin-based sensitizing medium. After photosensitizing and solvent development, a blind hole is made (Photo-Via), and the copper electroplating and etching circuits are added. Into a blind hole interconnected with the bottom layer. Repeatedly to complete the "successive layered" multilayer board. This method was developed by IBM at the Yasu plant in Japan in 1989 and can reach a line width of 3 mil/3 mil and a hole diameter of 5 to 10 mil. In addition, Japanese Ibiden company also had a similar "photosensitive hole" method in the same year, known as AddtiveBuildProcess (AAP/10). It is said that its line adhesion is three times stronger than SLC.
2.2 FilmRedistributionLayer (FRL)
The use of epoxy-type Photoactive Dielectric ("PID") and chemical copper additions completes the build-up of "Photovia" on existing FR-4 double-sided boards. Aperture of about 5-10mil, line width of up to 3mil/3mil. The finished board can be assembled with high density. This law was developed by IBM's Endicott factory in 1992 and went into mass production in 1995. The system was changed to water soluble imaging to reduce the disadvantages of SLC solvent imaging. Later TBM's Austin plant in Texas was changed to the addition line of chemical copper and copper electroplating, referred to as the ALR (Alternative Laminar Technology) method, and it is now in mass production.
2.3 MicrofilledVia (Mfvia)
The FR-4 is printed on both sides of the DF-4 double-sided panel, and the PID is formed by photosensitizing the holes and filling the silver paste into columnar conductive materials. After drying and leveling and pressing the copper foil together, the interconnection with the inner layer can be obtained, so that the outer layer circuit can be further completed to complete the MLB. This "blind hole" method, in which the copper foil and the silver paste cylinder are pressed and turned on, can eliminate the trouble of PTH and copper plating. This method is currently only used on Prolinx's V-BGA products. Two companies in Taiwan are currently mass producing. The silver content and quality of the silver paste used above are much higher than those of ordinary "silver through holes" for low-order dual-panel applications. Another Japanese CMK introduced SPM "silver paste multilayer board" also uses high-grade silver paste as the interconnection, but it is used to fill the full through-hole, and the aforementioned is not exactly the same.
3 Research Progress of UV Curing Inks for Laminates
The necessary functions of the UV-curable ink for the formation of the photoconductive vias involve various aspects. First, photosensitivity is required, and adhesion properties to the copper layer and the electrical properties of the insulating film must be ensured. At present, most of the UV curable inks used for the laminates are epoxy materials. The thickness of the BUM organic resin insulation layer made of it is between 50 and 100 Î¼m.
Photosensitive insulating resin materials are available in two forms: liquid and dry film. The liquid photosensitive resin has a good thickness and can be molded to control viscosity, molecular weight, etc. The disadvantage is that the manufacturing process is complicated. The flatness of the dry film product after photocuring is not as good as that of the liquid product, but it can simplify the production process of the BUM insulation layer and reduce the cost. At present, BUM's industrial production is still mostly using liquid photosensitive resin. The following further describes the properties and applications of liquid photosensitive insulating resins that have been commercialized.
3.1 Hitachi Chemicals Liquid Insulating Resin BL-8500, BL-9700
The product uses acid-modified epoxy acrylic resin as the main material, the formulation also includes materials to improve the adhesion, improve the resolution and flatness additives. BL-8500 is applied by screen printing. The amount of cloth required is 400-600mj/cm2. When the thickness of the insulating layer after drying is 55 Î¼m, the resolution can reach 60 Î¼m. The glass transition temperature (Tg) of the cured film was 150Â°C. The relative permittivity (Îµ) is 4.2 (at 1 MHz). BL-9700 is a new product that was launched in 1997. Its glass transition temperature (Tg) can reach 160-170Â°C. And the coating has a high elasticity.
(to be continued)
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