JPS63164292A - Method of selectively forming small holes in polyimide/kevlar substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method of forming small diameter holes in a polyimide/Keplar substrate using high temperature AA sulfuric acid, which is necessary for smoothing uneven edges of the holes. Honing is done by.

BACKGROUND OF THE INVENTION The use of bath liquids to form small diameter apertures in polyimide substrates is disclosed in U.S. patent application Ser.
No. (filing date: December 9, 1985).

This works well as long as it accomplishes its purpose.

[Problems to be solved by the invention]

However, the above disclosed methods are insufficient for forming small diameter apertures in polyimide/Keplar substrates.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for forming small diameter apertures in a polyimide/Keplar substrate having an adhesively applied metallic layer. Note that Kepler is a polyamide material and is a trademark of E.I. De & Bonn.

[Means and operations for solving the problem] The method includes forming at least one aperture of a predetermined size in a polyimide/Kepler substrate having a metallic layer adhesively coupled to the polyimide/Kepler substrate. do. Adhesives may be used, and in preferred embodiments B-stage (
Covered with partially cured polyimide. The method suffices to form at least one aperture in the metallic layer to expose the underlying polyimide/Keplar substrate layer, followed by forming one hole, preferably a small diameter hole, through the substrate. hot concentrated sulfuric acid during drilling at a temperature and time that is insufficient to penetrate or undercut other parts of the substrate, and insufficient to materially damage the substrate itself. contacting the exposed adhesive and the polyimide/Keplar material.

After this contacting step, the method preferably contacts a liquid honing medium with apertures of a predetermined size and shape in the polyimide/Keplar substrate to smooth the rough edges of the pores, if necessary. Preferably, the step comprises:
Liquid honing involves advancing an abrasive slurry through the hole at a rate and temperature sufficient to smooth any uneven edges around the hole and remove any material remaining in the hole. Preferably, the liquid honing agent is micron-sized alumina in a water slurry and is preferably directed through the pores for a moderate amount of time and pressure.

The medium used to form pores in the polyimide/Keplar substrate is hot concentrated sulfuric acid. The temperature of the sulfuric acid should be at least 185°C, preferably at least 190°C, and its concentration should be at least about 80°C, preferably at least about 85%, and more preferably at least about 90%. The minimum temperature of the sulfuric acid should be high enough to avoid decomposition of the sulfuric acid, and at room temperature and atmospheric pressure,
Preferably it is at least about 165°C. The sulfuric acid concentration should be high enough to protect the sulfuric acid from evaporation below the processing temperature. The polyimide/Keplar substrate is exposed to the sulfuric acid after copper cladding removal for a time sufficient to form the apertures, but to avoid decomposition and undercutting of the substrate. Preferably,
These times range from about 2 seconds to about 20 seconds for an 8 mil thick adhesive/substrate. (8 mil is 2.0 x I
Q-"eM) The method of the present invention is effective for forming holes in copper clad-loimide/Kepler substrates such as circuit boards, particularly when the substrate has a diameter from about 4S to about 16 Mil (4,
Thickness in the range of 1X10 51) and approximately 4 mils (1,0x
The apertures are formed with diameters in the slightly larger size range H from lO51), and the minimum edge distance between the apertures is approximately 6 mils (1,5X IQ"" am). It is. With such substrates, there is an inherent need to avoid undercutting or penetrating the substrate around the apertures of the desired size, shape and placement.

This method is applied to so-called blind holes and through-holes in copper-clad or other metal-clad I-diimide/Kepler substrates such as circuit boards consisting of substrates with adhesively bonded metallic layers on either side. This makes it possible to form both types. The blind hole travels once through the metal cladding and the substrate, but never again through the metal cladding on the other side of the substrate directly opposite the aperture formed in the metal cladding. The through hole passes completely through the product, meaning that the hole passes through the first aperture in the metal cladding on one side of the product, through the substrate directly below the aperture, and then through the first aperture in the cladding. means proceeding through a metal layer that is in register with (i.e. directly opposite) the metal layer.

The method of the invention makes it possible to form both so-called blind holes and so-called through holes in copper-clad or other metal-clad polyimide/Keplar products. The blind hole travels once through the metal cladding, the adhesive layer and the underlying polyimide/kepra layer, but never through the metal cladding on the other side of the product directly opposite the aperture formed in the metal cladding. It doesn't progress.

A through hole passes completely through the product, meaning that the hole passes through the first aperture in the metal cladding on one side of the product, through the adhesive layer directly below the aperture, and through the adhesive layer directly below the aperture. through the polyimide/Kepra layer, through the adhesive layer on the other side of the polyimide/Kepra layer, and then through the metal layer in register with (i.e., directly opposite) the first aperture of the cladding. means.

〔Example〕

FIRST EMBODIMENT The inventor has developed a 0.005 inch (12,7 x 10-
'cIn) flat with 1? 0.0015 inch (3,8X10
Qn) in a copper cladding of approximately 0.01 inch (
2,54X10 cIn) to 0.02 inch (5,
A play measuring 1 inch (2,54 cM) by 1 inch was formed consisting of holes having diameters centered around 08 x 1010-2C. The substrate is clad on both sides and the holes in the steel cladding are registered with respect to each other to promote through hole formation in the copper clad substrate by etching with iron chloride on both sides of the substrate. formed by joining together. After forming apertures in the copper cladding on both sides of the substrate, the copper cladding serves as a mask for the removal of the preimide/Kepler substrate material from the formed apertures.

Thereafter, the substrate having a hole pattern of a predetermined size, shape and spacing was placed in a concentrated sulfuric acid bath at 195°C for 10 seconds.
Soaked. This sulfuric acid concentration is 96%. After removing the substrate from the sulfuric acid bath, the substrate is 90% free of all sulfuric acid components.
It was submerged in water for 1 minute to remove and stop the reaction between the polyimide/Keplar substrate and the sulfuric acid.

Then it consists of an aluminum oxide slurry. The jagged edges in each aperture in the substrate were cleaned with a liquid honing medium. In this case, the nozzle of the hose supplying the liquid honing medium was maintained at a distance of at least 9 inches (22,86 cm) from the 6 holes at all times. The honing pressure was also maintained in the range of about 10 to about 50 psi, or about 0.68 x 10' to about 3.4 x 10' or skull.

Thereafter, the through-hole portion was treated with a non-electrodeposition copper deposition method and plated to a regular thickness.

Microphotographs of each hole showed that the through-hole formation was acceptable.

Second Embodiment The inventor measured 0.0015 inches (3,000 cm) on each side.
8x10 cm) with copper cladding, thickness o, o
0.004 inch (], 02X1 on a flat polyimide/kepler substrate of os inch (1,27
0 cIn) to 0.010 inch (2,54x1o
A hole measuring 1 inch (
A 2,54 on) x 1 inch array was formed.

After etching the steel cladding to promote through-hole formation, the copper cladding serves as a mask for subsequent treatment with sulfuric acid.

Next, the substrate with a patterned play of apertures in the steel cladding on each side was heated to 195 °C (96
%) immersed in a sulfuric acid bath for 7 seconds.

Immediately after removing the substrate from this sulfuric acid bath, all the sulfur f! l! Soaked in water for 1 minute to remove.

The rough material was then swept away from each edge of the formed hole with a liquid honing medium containing aluminum oxide abrasive particles dispersed in water. In this case, as in the first embodiment, the nozzle of the liquid honing feeder is maintained at least 9 inches (22,86 cWI) from the 6-hole at all times, and the honing pressure is in the range of about 10 to about 50 psi. held.

The holes formed in this substrate were then processed by a non-fusing copper deposition method and plated to a specified thickness. Microphotographs of a cross-section of this substrate showed that the plated through-holes could be accommodated.

When the inventor tried to reproduce the results of the first example using a 150°C sulfuric acid tank, he found that the sulfuric acid tank
The polyimide/Keplar material was not removed from the pores formed in the steel cladding even after 00 seconds of soaking.

Etching at 160° C. for 2 minutes and 45 seconds destroyed the polyimide/Kepler substrate between each hole as well as inside the hole, leaving only the steel cladding. When etched at 185°C for 20 seconds, the polyimide/
No through holes were formed in any of the Keplerian substrates. However, it was then possible to form such apertures by applying liquid honing to the apertures in the cladding without significant undercutting or seepage of the polyimide/Kepler substrate between each hole.

〔Effect of the invention〕

Thus, as detailed above, the present invention provides a method for sufficiently and effectively forming small diameter holes in a polyimide/Keplar substrate having an adhesively deposited metallic layer.

Claims (1)

[Scope of Claims] 1. A method for forming holes of a predetermined size and shape in a polyimide/Keplar substrate having a bondingly connected metallic layer, comprising: (a) at least one opening in the metallic layer; (b) at a temperature of at least about 185° C. for a sufficient time to form apertures of a predetermined size and shape in the polyimide/Keplar layer; (c) contacting the exposed polyimide/Keplar material in hot concentrated sulfuric acid, and removing the substrate from the sulfuric acid and washing with water; (c) removing the polyimide/Keplar material remaining in the openings; Optionally, contacting the substrate with a liquid honing medium. 2. A method for forming at least one aperture of a predetermined size and shape in a polyimide/Kepler substrate, the method comprising: (a) attaching a mask having at least one aperture of a predetermined size and shape to at least one of the substrates; (b) immersing the masked substrate in hot concentrated sulfuric acid at a temperature and time sufficient to form the at least one aperture beneath the at least one aperture; removing the substrate with the mask from the sulfuric acid; (c) cleaning the substrate to remove substantially all the sulfuric acid from the substrate; and (d) removing any polyimide/polyimide remaining in the openings. optionally contacting the substrate with a liquid honing medium to remove Keplerian material. 3. said polyimide/Kepler substrate having a first metallic layer adhesively connected to a first side of said substrate and a second side of said substrate opposite said first side; 3. A method according to claim 1 or 2, comprising a second metallic layer. 4. The method according to claim 3, wherein at least one of the holes is a blind hole. 5. At least one of the holes is a through hole, and the through hole is created by forming at least two apertures in each of the metallic layers that are registered on opposite sides of the substrate; and 4. The method of claim 3, wherein the portion of the substrate between the two apertures is removed.