Introduction:

The subtractive process has increasingly struggled to meet the demands for high-density flexible substrates in miniaturized and high-performance packaging devices. As a result, the semi-additive process has become more widely used in the manufacturing of high-density flexible substrates.

Semi-Additive Process:

Traditional flexible substrate circuit formation primarily uses the subtractive method, which is characterized by isotropy. In this process, when copper foil is etched in the vertical direction, the copper beneath the photoresist is also etched, a phenomenon known as “side etching,” which limits the precision of the circuit.

Currently, copper foil is widely used in the industry. It can reduce side etching to some extent, improving the subtractive method’s ability to create fine lines. However, as copper thickness decreases, so does the cross-sectional area of the circuit, which increases the DC resistance. This also negatively impacts high-speed signal transmission.

In contrast, the semi-additive process forms conductive patterns by plating within the openings of the photoresist. The width of the lines is determined by the width of the photoresist openings. Using high-resolution photoresist dry films can meet both high-density and high-speed requirements simultaneously.

The main process flow of the semi-additive process can be summarized as follows:

• Form a conductive layer by sputtering a metal buffer layer onto the polyimide substrate.
• Use image transfer technology to form a plating-resistant dry film pattern on the buffer layer.
• Perform electroplating to thicken the copper conductor lines.
• Apply differential etching to fabricate the line layer.

The formation of the buffer layer is a key step in the semi-additive process. Ensuring the consistent thickness and strong adhesion of the buffer layer to both the polyimide substrate and the photosensitive dry film requires continuous testing and process optimization to identify the optimal parameters.

Ultrathin Flexible Substrate Manufacturing Process:

With the ongoing miniaturization of electronic devices, reducing chip sizes has become an inevitable trend. As chips shrink to 50μm or even thinner, they become more susceptible to damage from the small stresses and strains generated by the substrate.

Flexible substrates offer significant advantages over rigid substrates, as they can bend in tandem with the chip. This flexibility greatly reduces the stress-induced damage to the chip, making flexible substrates ideal for these applications.

If you have any questions about PCBs and PCBA, feel free to contact me at info@wellcircuits.com.