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Drill Fundamentals
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DRILL FUNDAMENTALS

FEED RATE

An important aspect of the drilling operation is the user's ability to program the machine's z-axis to stroke with different drill diameters at different rates. These rates are typically engineered to achieve the best in output and hole quality while avoiding tool failure or breakage. Measured in inches per minute (ipm), feed rates depend on the tool diameter, machine capability and stability, laminate material type, copper layers, and stack height (see formulas.)

SPINDLE SPEEDS

Spindle speed settings control the rotation of the drill bit during the drilling cycle. Measured in revolutions per minute (rpm), speed also impacts the quality of the drilled hole as well as the drill bit's cutting edge condition. High speeds can result in excessive cutting edge corner breakdown, or "rounding". This is an undesirable condition, resulting in the drill "punching" rather than shearing through the material stack. Particulate materials drill or fabricate favorably with certain cutting speeds and should remain constant throughout the drilling range except when limited by the spindle capability (see formulas.)

RETRACT RATES

The z-axis return stroke can be programmed as well. This rate, known as retract rate and is measured in inches per minute (ipm) and should be set to a value that will minimize the duration of the drill bit inside the hole. Z-axis stability and drill bit diameter often influence optimum retract conditions. An unstable z-axis or a well worn z-axis can lead to poor depth control, poor hole quality, and high breakage occurrences. Most effected are the micro and small drill bit diameter range (.002"-.020".)

HIT COUNT

The number of holes or hits a drill bit can produce depends highly on the material through which it is drilling, the feeds and speeds, and the hole quality criteria that a PCB manufacturer has predetermined as its specification. Each drill stroke results in added wear, causing the cutting edge to become slightly less effective. Typically hit count ranges are from 1,000 to 2,000 hits for "via" diameter range (0.0130" - 0.0300") and 1,500 to 3,000 for "component" diameter range (0.032" - 0.050".)

Z-AXIS OFFSETS

Controlling penetration into the stack of panels is a key aspect of good drilling process. Minimum desired depth into the backup material for each drill bit is the amount of distance it takes to clear the point angle. This will ensure that the drilled hole has not been drilled shallow. Entering this value into the controller as a z-axis offset will go a long way in controlling penetration into the backup material. The point clearance is directly related to the drill bit's diameter and point angle. As the diameter increases, so does the distance needled to clear the point angle (see formulas.)