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| Typical Substrate Size: | 4.5 in. X 4.5 in. - Sizes up to 16 in. square can be processed. |
| Typical Substrate Thickness: | 0.010 in. to 0.060 in. |
The processing of arrays involves the registration of the substrate at each operation. Precise alignment at each step is of critical importance. Alignment is typically accomplished by registering the part against three pins where two are located along one edge of the part and one on an orthagonal edge. Since "as fired" or scribed edges may lack the required precision, an additional step to laser machine alignment flats may be required. The figure below (fig. 1) shows substrate alignment flats registered against the alignment pins.
SCRIBE CHARACTERISTICS
A laser scribe line consists of a series of small, closely spaced holes in the substrate that are produced by pulses of laser energy. Viewed under magnification, the scribe holes should appear essentially clean and free of recast. Under backlighting a plugged hole will appear dark. An occasional plugged hole will not affect the scribe. Hole depth is controllable and should generally be 1/3 to 1/2 of the substrate thickness.
SEM PHOTO OF SCRIBED HOLE
The SEM photo above shows a cross-section of the tapered hole that has been created by the penetration of a laser pulse into the substrate. The minor amount of slag shown on the substrate surface has been deposited around the hole as a result of the melt. The slag is benign, and is usually removed by a scraping process if the substrate has not been metallized.
The hole depth can be measured by inking the scribe line with a black marker pen, snapping the substrate at the scribe line, and viewing the cross section with a calibrated microscope.
LAYOUT /LOCATION OF SCRIBE LINES
The distance from a scribe center line to the edge of other features such as holes, cutouts, or metallization should be 0.010 to 0.050 inch minimum, depending upon the part design.
The border width or distance from the last scribe line to the edge of the substrate should be 0.100 inch, minimum. The border areas are shown in the figure below. Alignment flats have been laser machined into the borders to permit precision alignment of the substrate into work fixtures.
It is recommended that the scribe lines should completely cross the border areas to produce a good break and clean, square corners when the parts are singulated.
THE FINISHED PART
In the drawing above, the finished part is shown as being separated from the array. A corner of this part is magnified to show the somewhat rough edges that normally result when singulating a part from a scribed substrate. In applications where the edge roughness must be overcome, the scribe lines can be laser machined at an increased cost.
SUBSTRATE COATING
Substrates are generally coated with a water soluble material to protect them during scribing, breaking, machining or shipping. The coating may be removed by water wash. Normally, the coating is removed by Accu-Tech unless otherwise specified by the customer.
SCRIBING AND ALIGNMENT OPTIONS
- AS-FIRED EDGES - The laser scribe pattern is located on the substrate in relation to the original edges. Two adjacent edges on the substrate are used to form a reference corner. The entire substrate can be utilized with this method but the alignment accuracy irregularities in the original edges.
- SCRIBED EDGES - After scribing the substrate, the borders are broken off to produce accurate outside reference edges for subsequent operations.
- ALIGNMENT FLATS - Alignment repeatability can be improved by the addition of precision, laser machined flats along the outside reference edges of the substrate. These flats provide a smooth, accurate surface to make contact with tooling pins. The expense of having to laser machine the entire substrate edge is avoided.
- POST SCRIBING - Using this method, the scribe lines can be optically aligned to substrate metallization or other surface features such as holes, edges or other existing scribes.
SINGULATION OF THE SUBSTRATES
Even with the best scribing, the ability to hold extremely tight tolerances after the break will depend on the substrate material and the skill of the operator. Skilled hand breaking is usually preferred to machine breaking.
Common effects of breaking that cause a variation from a "perfect" straight line are hooks or flares, breakouts, and chips. The majority of these defects occur at the ends of the scribe line and the corners where scribe lines cross each other. The examples below show common variations encountered when breaking substrates. The specifications section below provides cost effective guidelines for acceptance.
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| HOOK AT CORNER | CHIP AT CORNER |
INSPECTION OF SCRIBED SUBSTRATES
The following equipment or its equivalent is recommended for the inspection of scribed and/or broken substrates.
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- Micrometer |
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- Optical Coordinate measurement machine |
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- Microscope with calibrated graticule |
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- Calipers |
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- Parallel Plates |
TOLERANCES FOR SCRIBING
The SPECIFICATIONS and TOLERANCES provided in the table below will generally produce the MOST COST EFFECTIVE laser processing. Tighter tolerances may be achieved at an increased cost and leadtime. All dimensions and tolerances are given in decimal inch units. Metric units are also available.
| SUBSTRATE THICKNESS |
DEPTH
OF SCRIBE |
DEPTH TOLERANCE +/- |
PULSE
(1) SPACING 96+% AL2O3 |
PULSE
(1) SPACING 99+% AL2O3 |
MAX CHIPOUT |
FINISHED PART BREAKOUT |
| .010 | .004-.006 | .001 | .005 | .005 | .005 | +.005/-.002 |
| .015 | .006-.008 | .001 | .006 | .005 | .008 | +.005/-.002 |
| .020 | .008-.008 | .002 | .006 | .005 | .008 | +.005/-.002 |
| .025 | .009-.012 | .002 | .006 | .005 | .010 | +.005/-.002 |
| .030 | .012-.014 | .002 | .006 | .006 | .010 | +.005/-.002 |
| .035 | .014-.016 | .003 | .006 | .006 | .010 | +.010/-.004 |
| .040 | .016-.018 | .003 | .006 | .006 | .010 | +.010/-.004 |
| .050 | .019-.023 | .004 | .006 | .006 | .012 | +.010/-.004 |
| .060 | .023-.027 | .004 | .006 | .006 | .015 | +.010/-.004 |
NOTE (1) Pulse spacing tolerance is +/- 0.001 in.
Surface Slag height, Max. . . . . . . .001
Scribe Location Tolerances
Note: All measurements made to a scribe line are made to the scribe centerline.
Scribe, line to line. . . . . . . . . . . +/-.001
Scribe, line to laser machined feature. . . . . . . . . . . +/-.002
Lasered feature to scribed exterior edge for ceramic thicknesses of:
.010 to .030 . . . . . . . . . +/-.003
.035 to .060 . . . . . . . . . +/-.005
Scribe line with respect to a fired edge. . . . . . . . . . . +/-.005
CL0694
© Accu-Tech 1997
Accu-Tech©
LASER PROCESSING INC.
1175 Linda Vista Drive
San Marcos CA 92078
Phone 760-744-6692
FAX 760-744-4963
Modem 760-744-6498
WWW.ACCUTECHLASER.COM