Stepped PCB Drill Geometry for Rigid Small-Hole Through Drilling
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Solution Overview
Problem
Existing drills for forming through holes in glass fiber reinforced substrates face challenges in achieving sufficient bending rigidity to penetrate thick substrates, especially when forming small-diameter holes at narrow pitches, leading to drill bending and incomplete penetration.
Innovation Solution
A drill design featuring a cutting edge with a larger diameter than the neck part, a single continuous chip evacuation groove with a main L-shaped groove and a secondary U-shaped groove that merges into the main groove, and a web taper of 0.022-0.024, enhancing bending rigidity and chip evacuation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional drill design is used, then the drill can be manufactured with simple structure, but the drill lacks sufficient bending rigidity to penetrate thick glass fiber reinforced substrates
Solution Approach 1:
The drill body is segmented into distinct portions with different diameters: a cutting edge portion with larger diameter for rigidity, a neck portion with smaller diameter for flexibility, and an intermediate portion connecting them. This segmentation allows each section to serve its specific function while achieving overall high bending rigidity for penetrating thick substrates.
Solution Approach 2:
The drill employs an asymmetric diameter distribution along its length, with the cutting edge portion having a significantly larger diameter than the neck portion. This asymmetric design creates a step structure that concentrates rigidity where needed (at the cutting edge) while maintaining manufacturability through standard drilling processes.
2Object-generated harmful factors
If multiple chip evacuation grooves are used, then chip evacuation performance is improved, but the drill structure becomes more complex and bending rigidity decreases
Solution Approach 1:
The single continuous chip evacuation groove is segmented into a main groove and a secondary groove that merges into it. The main groove extends from the front end over the step to the neck part, while the secondary groove extends along the main groove and merges at the neck part. This segmentation enables effective chip evacuation through both grooves while maintaining the integrity and rigidity of the drill body.
Solution Approach 2:
The secondary groove merges into the main groove at the neck part, creating a combined chip evacuation system. This merging allows chips to be evacuated through either groove while maintaining a single continuous path, achieving effective chip removal without the structural complexity and rigidity loss associated with multiple independent grooves.
3Strength
If the cutting edge diameter is increased to improve rigidity, then bending rigidity is improved, but the drill cannot form small-diameter holes at narrow pitches
Solution Approach 1:
The drill body is segmented with the cutting edge portion having a larger diameter for rigidity, while the actual cutting edges at the front end are positioned to create small-diameter holes. The intermediate portion with reduced diameter connects these elements, allowing the drill to maintain overall rigidity while achieving small hole diameters and narrow pitches through precise cutting edge positioning.
Data Source
AI summary
A drill for forming through holes in a glass fiber reinforced substrate includes a drill body having a cutting edge part on a front end side, and a neck part on a base end side. The cutting edge part has a larger diameter than the neck part. The drill body has a step formed between the cutting edge and neck parts and a single continuous chip evacuation groove having main and secondary grooves. The main groove has an L-shaped cross section and is extending from front end of the cutting edge part over the step to the neck part. The secondary groove has a U-shaped cross section and smaller groove width and depth than the main groove and is extending along the main groove from the front end of the cutting edge part over the step to the neck part and merging into the main groove at the neck part.