TCT Drills - Back Drilling

Posted Jun 16th, 2021

The benefits of TCS Lip Correction Geometry for back drilling are many but the most important is the improvement it provides in minimizing bird-nesting and reducing the amount of debris in the hole. Check this out below along with the appropriate photos to see what we mean. And of course, please call us to learn more on how we love talking about our principals and their great products and services.

Back Drilling and the Effects of the Correct Drill Angle

Back drilling is commonly used to reduce the effective length of the copper via and improve impedance. The negative effect of drilling out the back section of a plated hole, typically, results in large copper strings wrapped up on the drill bit from the thin copper wall plating. This effect can be reduced by changing the Lip Correction Geometry of the drill bit, as well as opening up the particle removal grooves in the drill bit.

The benefit of Lip Correction Geometry is a significantly heavier, chip removal rate which minimizes bird-nesting. The thinner web along the drill promotes reduced debris in holes while providing a larger volume for the vacuum to remove the copper strings. The special drills are available in 150°, 165°, 172° Point Angle for reduced point triangulation. The flatter the drill entry point angle, the shorter and more accurate the remaining stub tapered length. The back drill is designed with stronger cutting lips to improve overall tool life. Two different drill bits are available; the SSFI for back drilling of non-filled vias, and UCBD for non-conductive filled vias.

Back Drilling: The two photos above demonstrate the effect of web thickness and point angle on Rats Nest residue clinging to the drill bit.
Through Via Diameter: 0.0098”
Plating Thickness: 0.001”
Plated Hole Diameter: 0.0078” 
Back Drill Diameter: 0.0158”

The effect of the drill point angle on stub length is very important. As the angle of the drill point is flatter, the length of the angled copper and FR4 left inside the via, decreases; i.e. your drill is more like an end mill than a typical, steep angled drill for creating through holes in FR4. The improved via hole with less tapered copper results in tighter impedance numbers and less debris in the via.

About TCS

TCT Circuit Supply (TCS) is a proud supplier of industrial leading materials and equipment to the printed circuit board industry. As a wholly owned subsidiary of the TCT group and working with partners all over the world, TCS offers materials, technical support, and solutions for the most challenging applications. In addition to a wide variety of cutting tools and repoint services manufactured by TCT, we offer a portfolio of laminates, prepregs, films, pads, and consumable products.

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