Introduction:
The substractive process has been gradually unable to meet the processing requirements of high-density flexible substrates for miniaturization and high-performance packaging devices, and the semi-additive process has been increasingly applied to the manufacturing process of high-density flexible substrates.
Semi-additive Process:
The circuit formation of traditional flexible substrates adopts the subtractive method, which is mainly characterized by isotropy. That is to say, when etching copper foil in the vertical direction, the copper foil under the photoresist is also etched at the same time, which is often referred to as "Side Etching", which largely restricts the circuit elaboration.
At present, copper foil, the base material popular in the industry, can reduce the size of side etching to a certain extent, so as to improve the ability of the subtraction method to make fine lines. But at the same time, as the overall copper thickness decreases, the cross-sectional area of the circuit decreases correspondingly, which to some extent increases the DC resistance of the circuit. It is also unfavorable to the transmission of high-speed signals. In contrast to the subtractive method, the semi-additive method is to form a conductive pattern by plating in the opening of the photoresist. The line width basically determines the opening width of the photoresist, and the use of high-resolution photoresist dry film can meet the requirements of high density and high speed at the same time.
The main process flow of semi-additive process can be summarized as follows.
(1) A conductive layer is formed by sputtering metal buffer layer on polyimide substrate.
(2) Image transfer technology was used to form anti-plating dry film pattern on the buffer layer.
(3) Carry out graphic electroplating process and thicken the copper thickness of conductor line.
(4) Differential etching technology is adopted to realize the fabrication of line layer.
The first step is the formation of buffer layer is the key to the semi-addition process. How to ensure the consistency of the thickness of buffer layer and the binding force with polyimide substrate and photosensitive dry film requires constant process tests and optimization to explore appropriate process parameters.
Ultrathin Flexible Substrate Manufacturing Process:
With the miniaturization and miniaturization of electronic products, chip size reduction has become an inevitable trend. When the chip is reduced to 50um or even thinner, the chip may be damaged by the small stress and strain generated by the substrate. Flexible substrates have incomparable advantages over rigid substrates and can be bent with the bending of the chip, which greatly reduces the damage caused by stress of the substrate to the chip.
