1. Introduction
TMM® laminates are high-performance, ceramic-filled thermoset polymer composites specifically engineered for microwave and RF circuit applications. Their unique composition—combining a hydrocarbon matrix with a high ceramic filler content—provides exceptional dimensional stability, low thermal expansion, and a broad range of dielectric constants.
However, the abrasive nature of the ceramic filler requires careful attention during the routing process. Appropriate tool selection, surface speed, and chip load are critical to achieving clean edge profiles, minimized delamination, and extended tool life. With optimized parameters, tool life exceeding 250 linear inches can be achieved when machining TMM-10 laminates, while lower dielectric grades (such as TMM-3) yield somewhat shorter tool life.
2. Understanding Routing Fundamentals
2.1 Surface Speed (SFM)
Surface speed represents the velocity (ft/min) at the outer edge of the router bit.
Spindle Speed (RPM)=12×Surface Speed (ft/min)π×Tool Diameter (in)\text{Spindle Speed (RPM)} = \frac{12 \times \text{Surface Speed (ft/min)}}{\pi \times \text{Tool Diameter (in)}}
2.2 Chip Load
Chip load is the linear distance the tool travels per revolution, defining how much material is removed each pass.
Feed Rate (in/min)=Chip Load (in/rev)×Spindle Speed (RPM)\text{Feed Rate (in/min)} = \text{Chip Load (in/rev)} \times \text{Spindle Speed (RPM)}
Recommended Range:
• Surface speed: 200–400 SFM
• Chip load: 0.0010″–0.0015″ per revolution
Operating above 400 SFM may lead to excessive tool wear and degraded edge finish.
3. Recommended Routing Parameters
| Parameter | Recommendation |
|---|---|
| Tool Type | Diamond-cut carbide or spiral chip-breaker (≥5 flutes) |
| Lateral Chip Load | 0.0010″–0.0015″ |
| Surface Speed | 200–400 SFM |
| Entry Material | Phenolic, 0.010″–0.030″ |
| Exit Material | Phenolic, 0.100″ |
| Preferred Equipment | Excellon EX or equivalent precision router |
Note: Keep surface speed below 400 SFM whenever possible to maintain both edge quality and tool longevity.
4. Factors Affecting Tool Life
Several factors influence the useful life of a routing tool and the quality of the routed edge when working with TMM laminates.
| Factor | Effect | Recommendation |
|---|---|---|
| TMM Grade | Lower dielectric grades contain more abrasive filler and reduce tool life. | Use slower speeds and optimized geometries. |
| Surface Speed | High speeds (>400 SFM) increase wear. | Operate at moderate speeds (200–300 SFM). |
| Tool Geometry | More cutting edges improve durability. | Use ≥5-flute or diamond-cut designs. |
| Chip Load | Too high increases wear; too low causes copper burring. | Maintain 0.0010″–0.0015″. |
| Tool Size | Smaller tools wear faster. | Use larger tools whenever possible. |
| Stack Height | Thicker stacks add stress and reduce life. | Minimize stack thickness for precision routing. |
5. Useful Tool Life Estimates
The following data summarizes typical tool life expectations for various TMM grades and tool diameters. Values are based on 0.060″ laminate thickness. Doubling the thickness may reduce tool life by 50–60%.
| Material | Spindle Speed (kRPM) | Feed Rate (in/min) | 1/16″ Tool | 3/32″ Tool | 1/8″ Tool |
|---|---|---|---|---|---|
| TMM-3 | 15 | 19 | 80 | 120 | 120 |
| 20 | 25 | 50 | 50 | 50 | |
| 25 | 31 | 30 | 20 | — | |
| TMM-4 | 15 | 19 | 100 | 140 | 140 |
| 20 | 25 | 70 | 70 | 70 | |
| 25 | 31 | 45 | 40 | — | |
| TMM-6 | 15 | 19 | 150 | 180 | 180 |
| 20 | 25 | 100 | 100 | 100 | |
| 25 | 31 | 70 | 70 | — | |
| TMM-10 | 15 | 19 | 250 | 250 | 250 |
| 20 | 25 | 250 | 250 | 250 | |
| 25 | 31 | 250 | 250 | 250 |
Guidelines:
• Use lower spindle speeds (15–20 kRPM) for thicker panels.
• Replace tools more frequently in high-precision applications where edge finish is critical.
• Larger tool diameters generally provide better stability and longer service life.
6. Tool Geometry and Performance
Tool geometry has a significant influence on routing results. Tests show that multi-flute diamond-cut tools provide the best combination of long life and clean edge finish.
| Abbreviation | Generic Description | Vendor | Relative Tool Life |
|---|---|---|---|
| PCR1D | Diamond Cut (Down-Draft) | Precision Carbide | ★★★★★ |
| PCR1U | Diamond Cut (Up-Draft) | Precision Carbide | ★★★★★ |
| Mega RCS | Diamond Cut (Up-Draft) | Megatool | ★★★★☆ |
| Tuflon 44 | Spiral Chip Breaker (5 Flute) | Tuflon | ★★★☆☆ |
| Mega RI | Straight Endmill (3 Flute) | Megatool | ★★☆☆☆ |
| PCEM2 | Spiral Endmill (2 Flute) | Precision Carbide | ★☆☆☆☆ |
Recommendation: Avoid 2-flute tools commonly used for PTFE materials; they exhibit poor performance on ceramic-filled TMM laminates due to lower rigidity and smaller cross-section.
7. Tool Surface Speed Reference
| Spindle Speed (RPM) | 1/16″ Tool | 3/32″ Tool | 1/4″ Tool |
|---|---|---|---|
| 15,000 | 245 SFM | 368 SFM | 491 SFM |
| 20,000 | 327 SFM | 491 SFM | 654 SFM |
| 25,000 | 409 SFM | 614 SFM | 818 SFM |
Optimal Range: Maintain tool surface speed between 200–400 SFM for a balance between quality and wear.
8. Additional Observations
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Tool Diameter: Larger tools last longer due to increased rigidity and reduced localized heating.
-
Stack Height: Higher stack heights increase lateral loading—limit to two or three boards when possible.
-
Copper Burring: Avoid chip loads below 0.001″/rev to prevent excessive burr formation.
-
Dust Extraction: Use vacuum-assisted debris removal to prevent tool clogging and ensure smooth routing.
9. Best Practices Summary
✅ Use diamond-cut carbide tools with at least 5 flutes.
✅ Keep surface speed between 200–400 SFM and chip load 0.0010″–0.0015″.
✅ Avoid high spindle speeds; slower cutting extends tool life.
✅ Rout in multiple shallow passes for thick panels.
✅ Maintain rigid panel support and secure clamping.
✅ Employ air cooling and dust vacuum systems.
✅ Replace tools based on edge quality rather than total distance cut.
10. Conclusion
Routing TMM® laminates requires precise process control and proper tool management. The combination of moderate cutting speeds, optimized tool geometry, and effective dust extraction ensures superior edge quality, dimensional accuracy, and extended tool life.
By adhering to these routing guidelines, manufacturers can maintain the mechanical integrity and electrical reliability of microwave and RF circuits fabricated from Rogers TMM® laminates.
