US 3698976 A
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' Oct. 17, 1972 N. E. AKE ETAL 3,698,976
METHOD FOR SOR'IING DIE Filed March 19, 1971 NVENTORS NELSON E. A/(E BY HARRY C. kL/Nq United States Patent Otfice 3,698,976 Patented Oct. 17, 1972 US. Cl. 156-155 7 Claims ABSTRACT OF THE DISCLOSURE This is a method of removing unwanted die, which die are formed at the periphery of a wafer, from the remaining die which are formed Within that periphery. This is accomplished by attaching the wafer to a suitable backing material using a glue which is soluble in water, alcohol or trichloroethylene. The wafer is scribed and fractured into individual die, and a ring of cement is placed along the periphery of the wafer, which cement is not soluble in the above referred to solvents. The wafer is dipped in one of the above solvents so that the outer periphery of unwanted die stick together and the remaining die are individually removed.
BACKGROUND OF THE INVENTION This invention relates to an improved method for sorting die.
During the processing of semiconductor devices the wafer is scribed and fractured into individual die after the standard diffusion and metalization steps have been completed. However, those die which were formed along the periphery of the water are all generally defective and unwanted since there will be metal bridging around each of these die, together with cross diffusion along the edge thereby causing shorts in the final device. In the past, these unwanted die were separated from the remaining die, after scribing and fracturing, by manual and visual methods or by using exotic solutions wherein the good die will tfloat to the top or bottom of the solution and the unwanted die would become separated from the good die.
SUMMARY OF THE INVENTION It is an object of this invention to provide a more economical method of sorting unwanted die from the remaining die after scribing and fracturing the wafer.
According to a broad aspect of this invention there is provided a method of sorting die comprising the steps of attaching a wafer having a plurality of die formed therein to a suitable backing material using a first glue, said first glue being soluble in a first solvent, scribing and fracturing said water to form separate die, applying a second glue along the periphery of said wafer, wherein only said first glue is soluble in said first solvent, dipping said wafer and backing material into said first solvent for a sufiicient time so that the die along the outer periphery are still stuck together, 'while the remainder of the die within the periphery become separated from the backing material and from each adjacent die.
BRIEF DESCRIPTION OF THE DRAWING The figure shows the wafer glued to a suitable backing material.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the figure, a suitable backing material 1, such as paper, cloth or plastic may be used. In this example, we are using Velum paper made by Avery. When a cover backing is removed from the paper, there is a sticky glue on the paper which is soluble in standard solvents, such as water, alcohol or trichloroethylene. If the paper doesnt have any glue on it, a glue can be applied thereto, such as Eastman 910, which is a polyester material that is soluble in water. A wafer 2 containing a plurality of die is then attached to the backing material and held there by the glue which is soluble in the standard solvents. Using a standard scribing instrument and a standard fracturing tool such as Mech-el SF 101, the wafer is scribed and fractured into individual die, wherein each die is still stuck to the backing paper. Now a second type of glue or cement 3, which is not soluble in the above referred to standard solvents, is applied to the periphery of the fractured wafer. A typical and suitable cement for that purpose would be Ambroid cement, commonly known as airplane glue, whose major constituents are isobutyl acetate, isopropyl acetate and acetone. This cement, of course, is not soluble in any of the solvents such as water, alcohol or trichloroethylene, and is soluble in acetone.
Now the wafer and the paper are dipped into a solution such as the above solvents, i.e. water, alcohol or trichloroethylene, so as to dissolve the first glue.
When using standard Velum paper made by Avery with a sticky backing and a trichloroethylene solvent, the dipping process can be carried out in approximately three minutes. The backing paper is now removed and the die along the outer periphery of wafer remain stuck together by the Ambroid cement, and are thus isolated from the remaining individual die which are now loose. In case any of the Ambroid cement becomes attached to the good individual die, the separated. die should be washed two times with acetone to dissolve the cement which may have adhered thereto.
The separated die now are ready to be further processed and assembled in a suitable housing according to the standard assembly and packaging techniques.
It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.
1. A method of sorting die comprising the steps of:
attaching a wafer having a plurality of die formed therein to a suitable backing material using a first glue, said first glue being soluble in a first solvent; scribing and fracturing said wafer to form separate die; applying a second glue along the periphery of said wafer, wherein only said first glue is soluble in said first solvent;
dipping said wafer and backing material into said first solvent for a suflicient time so that the die along the outer periphery are still stuck together, while the remainder of the die within the periphery become separated from the backing material and from each adjacent die.
2. A method according to claim 1 wherein said backing material is a paper.
3. A method according to claim 1 wherein said first solvent is selected from a group consisting of water, alcohol or trichloroethylene.
4. A method according to claim 1 wherein said first glue is a polyester material which is soluble in water.
5. A method according to claim 1 wherein said second glue is a cement comprised of isobutyl acetate, isopropyl acetate and acetone, and said second. glue is soluble in acetone.
6. A method according to claim 1 wherein said first solvent is trichloroethylene and said wafer and paper are dipped in said first solvent for approximately three minutes.
3 4 7. A method according to claim 4 further comprising 2,984,897 5/1961 Godfrey 156-155 the step of: 3,600,246 8/1971 Breen 156 -265 cleaning each separate individual die with acetone.
DOUGLAS J. DRUMMOND, Primary Examiner References Cited 5 UNITED STATES PATENTS 2,865,082 12/1958 Gates 156-250 29 58315625 2,970,730 2/1961 Schwarz 29-580