Wet etch process and composition for forming openings in a polymer substrate

Abstract

A composition and method for etching a polymer substrate in particular for forming micro vias includes a dihydric alcohol having from two to five carbon atoms, a hydroxide compound selected from the group of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide and mixtures thereof, and water. In one embodiment the composition includes glycol, potassium hydroxide and deionized water, wherein the glycol and the water are present in a ratio of from about 0.5:1 to about 8.5:1 and the potassium hydroxide is present in an amount of from about 40 to about 80 grams per 100 ml of glycol and water solution.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001] The present application claims the benefit of U.S. Provisional Application No. 60 / 222,362, filed Aug. 1, 2000, the disclosure of which is hereby incorporated by reference herein.BACKGROUND OF THE INVENTION[0002] The present invention relates in general to the field of microelectronic elements, and more particularly, to chemical processes and compositions therefore for forming openings such as windows, vias and / or through holes in polymer substrates. Still more particularly, the present invention relates to etch compositions providing a color signal indicator at the completion of the etch process.[0003] Windows, vias and other openings are common features incorporated in microelectronic elements enabling the interconnection of microelectronic components and circuit features on opposing sides of a substrate, typically, a dielectric substrate such as a flexible sheet of polyimide. Micro-vias, i.e., those having a diameter of less than about...

AI Technical Summary

Benefits of technology

[0010] The present invention discloses glycol-based etchant compositions for etching openings, in particular, micro-vias, in polymer substrates. These etchant compositions have higher boiling points, by way of example, of preferably about 240.degree. F. to 300.degree. F., more preferably of about 260.degree. F. to 280.degree. F., and hence, are not highly volatile. The etchant compositions of the present invention are more stable than alcohol-based formulations, making them easier to control. In addition, glycol-based etchant compositions are less likely to attack the adhesive that are typically used in microelectronic elements and / or in bonding metal clad polyimide material to a glass frame. The method and etchant compositions of the present invention produce clean and even vias or openings in a two-step process, i.e., (1) dipping the substrate in the etchant composition, preferably until a red signal color covers the via opening and (2) rinsing with pressurized water, i.e., about 30 psi, until the red color when present disappears from the via.

Problems solved by technology

This two-step laser ablation process is not only time consuming, but also increases manufacturing costs.

In addition, laser ablation generally can only process one substrate at a time.

For a variety of reasons, these known etching solutions suffer a number of disadvantages wherein improvements in chemical etching techniques have been sought.

These alcohol-based etchants are hard to control due to rapid depletion of the active components.

Aqueous etching solutions such as known from U.S. Pat. Nos. 5,350,487, 4,911,786, 4,857,143 and 4,353,778 are effective in removing the polyimide material, but often cause contact pad blisters when used in forming vias in two metal polyimide structures, i.e., a polyimide substrate clad on its opposing surfaces with a copper layer, or when used with one metal polyimide structures.

Another problem with using aqueous etching solutions in single metal polyimide structures is that a mask, a resist or another protect layer must be used to protect the surface of the polyimide which is not metal clad.

Solvent-based etchants are therefore undesirable due to the tendency to separate the copper clad polyimide material from the glass frame.

In addition, these solvent-based etchants will have the tendency to cause the copper contact pads to form blisters by delamination of the contact pads from the polyimide substrate.

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