LAYOUT /LOCATION OF SCRIBE LINES
The distance from a scribe center line to the edge of other features such as holes, cutouts, or metalization 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.
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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.
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.
HOOK AT CORNER CHIP AT CORNER
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INSPECTION OF SCRIBED SUBSTRATES
The following equipment or its equivalent is recommended for the inspection of scribed and/or broken substrates.
Ceramic thickness Micrometer
Substrate Features, distances, locations Optical Coordinate measurement machine
Pulse spacing, Scribe Depth, Hole Taper, Pulse Hole Diameter, HAZ, Slag Height
Microscope with calibrated graticule
Breakout Tolerances Calipers
Camber Parallel Plates