|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. - Thicknesses greater than 0.100 can be processed.|
COST EFFECTIVE DRILLING OF HOLES
In order to achieve cost effective manufacturing, multiple parts are typically created on a single large substrate. The parts are then processed in batch form and later singulated into individual substrates by breaking along scribe lines. The processing of either individual substrates or arrays requires accurate registration at each operation.
SUBSTRATE ALIGNMENT OPTIONS
Several options for substrate alignment are listed below in order of increasing laser processing cost.
1. SCRIBED EDGES - After scribing the substrate, the borders are broken off to produce accurate outside reference edges for the subsequent processing operations.
2. AS-FIRED EDGES - The pattern to be cut by the laser 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 may be poor due to irregularities in the fired edges.
3. ALIGNMENT FLATS - The alignment repeatability can be improved for subsequent processing by the addition of precision, laser machined flats along the outside reference edges of the substrate. These flats provide a smooth surface to make accurate contact with the tooling pins. Using this method avoids the expense of laser machining the entire substrate edge.
4. POST ALIGNMENT - With this method, cut features can be optically aligned to the substrate metallization or other surface features such as holes, edges or other existing scribe lines. Accuracy is excellent.
Figure 1 illustrates a substrate designed with breakaway borders into which three alignment flats have been machined. The substrate is shown being registered against three alignment pins. For illustration purposes there are sixteen individual parts (defined by scribe lines) shown on the substrate. Each part contains six holes and a cutout that requires laser machining.
FIG. 1 - Substrate Registration using Alignment Flats
METHODS OF LASER DRILLING HOLES
There are two basic methods of creating a hole:
1. Pulsed or percussion method -
This method is suitable for drilling small round holes up to 0.005 in. by rapidly vaporizing the substrate material at high laser power. Hole creation is very fast and clean. The illustration in Figure 2 shows the crossection of a drilled hole. The hole shape is dependent on energy distribution within each laser pulse.
Fig. 2 - Crossection - Laser Cut Hole
2. Contoured or trepanned method -
This method is used to produce a hole of any size or shape. The method consists of selecting a punch- thru point inside the periphery of the feature, cutting to the feature edge, and then following the edge outline to complete the cut that defines the feature.
Fig. 3 - Photo of Laser Contoured Hole
THE ANATOMY OF A LASER CUT
The method of hole creations (either pulse or contour) does not materially affect the cross-sectional shape of the cut edge. The sketch in Figure 2 shows the cross-section of a typical laser cut edge. The laser beam has entered at the top and exited at the bottom. As the beam vaporizes the material, the entrance edge becomes slightly rounded. The cut also develops a slight taper. See the table on at end of this document for the taper vs thickness.
DESIGNING MACHINED FEATURES
Virtually any planar shape can be cut in ceramic substrates. These shapes include circles, curves, rectangles, polygons, rounded objects, thin slots, etc., and any combination of the above. Since ceramics are strong but brittle materials, the designer should consider a radius as large as practical on inside corners. All inside corners will have a minimum 0.002 in. radius due to the laser beam diameter. Rounding outside corners can also reduce chipping.
An important consideration when designing a machined feature is the location of the start and stop points for the cut. Some general guidelines:
In order to ensure a high yield of finished parts, the designer should attempt to maintain at least the minimum recommended distance between the edges of machined features. See the table at end of document for recommended values.
DEALING WITH SURFACE MATERIALS
Other materials may appear on the surface of a ceramic substrate or within the substrate and affect the cutting of the substrate. Examples include:
The effect of these materials may be minimized with proper layout and good laser machining techniques.
HANDLING AND CLEANING
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.
REMOVAL OF SLAG
Slag occurs when the substrate material is melted by the laser. Slag buildup is primarily found on the beam exit side of the substrate and is removed after laser processing.
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.
|TYPICAL EDGE TAPER EXCLUDING ENTRANCE ROUNDING||RECOMMENDED DIAMETER TOLERANCE (NOTE 1)||MAXIMUM CHIPOUT||MINIMUM FEATURE EDGE TO EDGE||MINIMUM FEATURE EDGE TO SCRIBE C/L||MINIMUM FEATURE EDGE TO METAL EDGE|
Note 1. Optical measuring techniques are generally used to verify these dimensions.
For tighter diameter control, pin gauges are recommended.
As a general rule it is helpful to coordinate and/or specify specific measuring methods when attempting to measure dimensions and tolerances of the magnitude shown here.
Feature location tolerance............ +/-.002, centerline to centerline.
Kerf width.................................... .004 +/-.001 measured at the beam exit side.
Slag.............................................. .001, Max. residual after removal
© Accu-Tech 1994
1175 Linda Vista Drive
San Marcos CA 92078