US2735763A - Process for manufacturing small parts - Google Patents

Description

United States Patent PROCESS FOR MANUFACTURING SMALL PARTS FROM THIN METALS Alfred E. Heath, Bordentown, N. 1., assignor to Radio Corporation of America, a corporation of Delaware No Drawing. Application October 27, 1954, Serial No. 465,127

6 Claims. Cl. 95-'-5.7)

This invention relates generally to the manufacture of small parts from very thin metals and, more particularly, to an etching process for obtaining small metal parts from a sheet of thin metal which will not withstand any mechanical working.

In the preparation of metal laminations, such as are used in magnetic recording heads for example, 'the laminations must be constructed of a very thin metal which is processed to have certain magnetic properties which are believed to be a function of the internal molecular structure of the metal. Such metals will not Withstand any mechanical working because such working disturbs the internal molecular structure resulting in a change of the magnetic properties of the metal and would require a reprocessing of the metal. It is desired therefore to provide a manufacturing process bywhi'ch such laminations may be obtained from a sheet of such prepared metal and during which process the metal will not be Subjected to undue strain or distortion.

The photo-etch process which is frequently employed in the manufactureof metal parts, is readily adaptable to the manufacture of these laminations. However in the process of etching the metal, a suitable backing must be provided to support the metal during the etching process and from which the small metal parts may be readily separated without being distorted.

Several attempts have previously been made to provide suitable etch resistive backings for the metal during the etching process. Gluing the metal to 'a phenolic board has been tried and rejected because in the separation of the laminations from the board they were bent to such a degree as to make them useless. Several methods of applying etch resistive backings comprise painting a heavy coat of acetate cement or paint on the back of the metal, or gluing paper or acetate cloth on the back of the metal. The method of removel of these backing's is to dissolve the backing in a suitable solvent. The use of such backin-gs has several disadvantages. They do not provide the stiffness required for etching in a paddle type eteher and the time involved for dissolving the backing and the number of washes required to clean the metal of the resistive backing material make the process unwieldy.

It is also desirable to provide a process for the manufacture of these small laminations which is readily adaptable to automation 'or assembly line methods.

An object bf this invention is to provide an improved process for the preparation of small metal parts by the photo-etch method which permits distortion free separation of the metal parts from their backing.

Another object of this invention is to provide an improved process for backing a metal sheet which provides the stiffness necessary for etching the metal and permits easy removal of the finished parts from the backing.

A further object of this invention is to provide an improved process for the manufacture of thin metal laminations which is rapid and inexpensive.

A still further object of the present invention is to pro- .vide an improved process for the manufacture of thin 2,735,763 Patented Feb. 21, 1956 metal laminations which process is adaptable to automatic assembly line methods.

In general the improved process comprises conditioning a surface of the metal, coating this surface with a photosensitive resist emulsion, exposing and developing the photo-resist, coating the untreated side of the metal with a substantial thickness of wax, etching the metal in a suitable etcher, and separating the metal parts from the wax backing by exposing the wax and adhering metal parts to a cold atmosphere or medium.

The novel features of the invention, as well as additional objects and advantages thereof, will be understood more fully from the following detailed description.

In the preparation of a metal for the photo-etch process the metal is first thoroughly cleaned by means of a tnchlorethylene degreaser for example. The cleaned metal may be chemically etched, by means of nitric acid for example, to roughen the surface in order that a coating may readily adhere thereto. The metal sheet is next placed in contact with a suitable backing, such as a Bakelite panel for example, and a photo-sensitive resist is caused to flow over one surface of the metal to completely cover the surface. The photo-sensitive resist is an emulsion which is applied as a coating to a surface and which will react to light of a predetermined intensity. After the coating has set, if a portion of the coating is exposed to light, the exposed portion undergoes a chemical change which causes it to resist dissolution by certain reagents which will dissolve the unexposed portions.

The sheet is then placed in a heating oven in order to harden this coating. The metal sheet is next placed on a clean backing, a Bakelite panel for example, and is covered with a negative. In the instant case the negative would be comprised of an opaque screen provided with transparent lamination patterns. These materials are then placed on a suitable exposure apparatus and exposed to light for a fixed period determined by the particular photoresist material. The exposed metal is then developed by spraying the exposed surface with a suitable solvent. The portion of the photo-sensitive coating which has been exposed to the light, namely the lamination patterns, will resist the action of this solvent and continue to adhere to the metal while the portion of the photo-resist which has not been exposed will be dissolved and washed away from the metal to again bare the metal between the lamination patterns.

The metal is now ready to be etched to produce the desired parts from the sheet. To provide the backing in accordance with the invention for the metals during the etching process, a sheet is laid face down on a glass plate or other smooth surface. A form is provided along the edge of the sheet and softened or molten wax is poured over the sheet within the form. A thickness of 3/ 32 to .4; inch has been found satisfactory. Two waxes which have been successfully employed in this process are Cerise AAA, a product of Socony Vacuum, and Sunwax 1290, a product of the Sun Oil Company. Both of these waxes are mineral base waxes.

By way of example, brass bars have been used to provide the form around the perimeter of the metal sheet to retain the wax when it is poured. This form serves as a mold or dam. It is desirable to treat the mold or dam with a mold release compound such as silicone grease in order that the mold may be readily removed after the wax has set. After the Wax has set, the form is removed and the wax backed sheet is then placed in a paddle type etcher, for example. This etcher causes an etching solution to be splashed over the metal and to dissolve the metal where it is not protected by the photo-resist coating. At the completion of the etching process, there exists the sheet of wax with the desired laminations adhering to one surface.

The critical point of the entire process is the separation of these laminations from the wax without bending or distorting them. This is accomplished by causing the wax to be supercooled to a temperature considerably below freezing and preferably to a point where the wax becomes brittle. Due to the difference in the coefficients of expansion of the two materials, wax and metal, one will contract more rapidly than the other causing the laminations to loosen themselves from the wax.

The cooling may be accomplished by merely placing the wax backed laminations in a cooling compartment. It has been found in practicing the present invention that the time required to cool the materials sufiiciently to produce the desired result is too long. An effective means of accomplishing rapid cooling is to dip the wax into liquid acetone which has been cooled by the introduction of Dry Ice. Acetone is rapidly cooled to a temperature of 70 C. by this method. A dipping for a period of not more than 5 seconds is sufficient. Other liquids which may be cooled to other temperatures would be equally effective.

The use of Dry Ice, which is solidified carbon dioxide, as a cooling agent for the liquid has an additional beneficial effect. When the relatively warm wax is placed in the cold liquid, it causes a bubbling action of the carbon dioxide which is in the liquid adjacent the Wax and this bubbling aids in freeing the laminations from the wax after they have initially broken loose due to contraction. Artificial agitation of the liquid will also serve to accomplish this result.

Another advantage in using a liquid as the cooling agent is that the laminations may be easily recovered from the liquid by providing a sieve type basket to collect the laminations as they drop away from the wax surface.

The final step in the process is to place the laminations in a solvent which removes the photo-resist coating therefrom.

It will be apparent that the above described process is a relatively simple process which is inexpensive and rapid in relation to other processes indicated herein. The process is also readily adaptable to production line methods since all of the steps are relatively simple.

What is claimed is:

1. In a process for manufacturing small parts from a thin sheet of metal, the steps comprising coating a surface of said sheet with a light-sensitive resist, exposing said coated surface to a light image in the nature of a pattern, removing the unexposed resist, backing said sheet with a substantial thickness of wax, etching away the metal sheet uncovered by the removed resist, and supercooling the wax backed parts thereby causing the parts to be released by the wax.

2. A process for manufacturing small parts from a sheet of thin metal comprising coating a first surface of said metal sheet with a light sensitive resist emulsion, exposing a portion of said emulsion through a negative having opaque portions, washing the unexposed portions of said emulsion from said surface, applying a backing of wax to a second surface of said metal sheet, etching completely away the portions of said sheet uncovered by the removed, unexposed emulsion thereby leaving metal parts adhering to said wax, and dipping the wax backed metal parts in a supercooled liquid whereby the parts are separated from said backing.

3. A process for manufacturing small laminations from a sheet of thin metal comprising applying a coating of light-sensitive resist emulsion to one surface of said sheet,

placing a negative having transparent lamination patterns over said surface, exposing said coated surface to light through said negative to provide exposed and unexposed portions of said emulsion, washing away the unexposed portions of said emulsion, applying a relatively thick layer of wax to the uncoated surface of said metal sheet, completely etching away the portions of the metal sheet uncovered by the removed, unexposed emulsion thereby leaving the laminations adhering to said wax, and dipping said wax into a supercooled liquid thereby causing said laminations to separate from said wax.

4. A process for manufacturing small laminations from a sheet of thin metal comprising applying a coating of light sensitive resist emulsion to one surface of said sheet, placing an opaque negative having transparent lamination patterns over said coated surface, exposing said coated surface to light through said negative, developing said exposed surface which comprises washing away the portions of said coating not exposed to light, applying a relatively thick backing of wax to the uncoated surface of said metal sheet, completely etching away the portions of the metal where the resist emulsion has been washed away thereby leaving the laminations adhering to the wax, and dipping said wax into a supercooled liquid thereby causing said laminations to separate from said wax due to different rates of contraction.

5. A process for manufacturing small metal laminations from a sheet of thin metal comprising cleaning a first surface of said metal, coating said first surface with a photo-sensitive resist emulsion, placing an opaque negative having transparent lamination patterns over said coated surface, exposing said coated surface to light through said negative, exposing said coated surface to a developing medium which dissolves and washes away said photo-sensitive resist which has not been exposed to light thereby uncovering portions of said first surface, applying a relatively thick coating of wax to a second surface of said sheet to form a rigid backing for said sheet, exposing said first surface to an etching medium thereby completely etching away the uncovered portion of said sheet from said wax backing, dipping said hacking into a supercooled liquid thereby causing said laminations to separate from said wax due to different rates of contraction, and washing said laminations to remove the photosensitive emulsion therefrom.

6. A process for manufacturing small metal laminations from a sheet of thin metal comprising cleaning a first surface of said metal, coating said first surface with a photosensitive resist emulsion, placing an opaque negative having transparent lamination patterns over said coated surface, exposing said coated surface to light through said negative, exposing said coated surface to a developing medium which dissolves and washes away said photosensitive resist which has not been exposed to light thereby uncovering portions of said first surface, applying a coating of wax to a second surface of said sheet to form a relatively rigid backing for said sheet, said wax coating having a thickness of at least 3/32 inch, exposing said first surface to an etching medium to completely etch away the uncovered portions of said sheet from said wax backing thereby leaving the laminations adhering to said backing, dipping said backing into supercooled acetone thereby causing said laminations to separate from said Wax, and washing said laminations to remove the photosensitive emulsion therefrom.

No references cited.

Claims (1)

1. IN A PROCESS FOR MANUFACTURING SMALL PARTS FROM A THIN SHEET OF METAL, THE STEPS COMPRISING COATING A SURFACE OF SAID SHEET WITH A LIGHT-SENSITIVE RESIST, EXPOSING SAID COATING SURFACE TO A LIGHT IMAGE IN THE NATURE OF A PATTERN, REMOVING THE UNEXPECTED RESIST, BACKING SAID SHEET WITH A SUBSTANTIAL THICKNESS OF WAX, ETCHING AWAY THE METAL SHEET UNCOVERED BY THE REMOVED RESIST, AND SUPERCOOLING THE WAX BACKED PARTS THEREBY CAUSING THE PARTS TO BE RELEASED BY THE WAX.