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Four kinds of exposed inner pad protection schemes for FPC multilayer boards

cheme I: printing anti etching ink

In the engineering design, the printing ink photos are printed on the screen through the photos. After the use of the screen printing anti etching ink, the curing parameters of the oven are set and it can be cured. When the figure of the FPC outer layer is made in the later process, the ink can be easily removed by the alkali solution, so that the bonding pad of the inner layer is exposed, realizing the protection of the bonding pad of the exposed inner layer of the FPC multilayer board.

Scheme II: Paste photosensitive dry film

The engineering design exposes the photos. After the boards are pasted with the photosensitive dry film, they are exposed through the photos; After development, the pads to be protected are covered with dry film; When making the FPC outer circuit, the photosensitive dry film can be directly removed. When designing the dry film exposure photos, ensure that the specification of the designed protective dry film is reasonable, make the dry film coverage area as large as possible, and prevent the inner bonding pad from being damaged or dropped due to the small protective dry film.

Scheme III: “Photosensitive dry film+anti etching ink” combination

The combination of “photosensitive dry film+anti etching ink” is used for protection, giving play to their respective advantages, so that the inner pad can be better protected and further improve the quality. First paste the photosensitive dry film for exposure and development, and then print the anti etching ink for curing. Among them, local location belongs to double protection. In addition, the dry film here has two functions:

(1) Protect inner pad;

(2) Fill the glue free area, fill the height difference between the inner and outer layers, increase the bonding force between the inner layer and the outer copper skin, and reduce the risk of plasma delamination bursting before PTH.

Scheme IV: Paste high temperature resistant tape

The bonding pad that needs to be protected in the inner layer shall be covered by strip pasting, and the high temperature resistant tape shall be manually torn off after the FPC outer line is made. The width of high temperature resistant tape can be purchased according to the demand, so as to facilitate the production of PCB companies; The high temperature resistant tape is pasted in the adhesive free area, and its length and width are slightly smaller than the length of the adhesive free window area



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