Check Your Manufacturer, Particularly for Combined Designs
In the intricate world of hybrid PCB manufacturing, the choice of drilling parameters plays a crucial role in ensuring precision, minimizing thermal and mechanical stress, and supporting downstream processes like plating. This article explores the key drilling parameters and their impacts on hybrid PCB fabrication.
Drill Type and Diameter
For thick or multilayer substrates in hybrid PCBs, diamond core drills or electroplated diamond drills are preferred due to their durability and effectiveness on composite or metal materials. On the other hand, laser drilling (using UV or CO₂ lasers) is employed for creating microvias with diameters often less than 0.15 mm in thin dielectric layers.
Drill Speed (RPM) and Feed Rate
Composite layers containing resin require lower rotational speeds to avoid heat buildup that can melt or distort resin materials. Excessive speeds or feed rates cause uneven forces, damaging the hole quality and tooling life. Optimal speeds balance efficiency and hole integrity.
Cooling and Lubrication
Thick materials (>1 inch or ~25.4 mm) require high-pressure coolant delivered via a water swivel adapter or multiple cooling directions (through drill center, sides, submergence) to prevent tool overheating and material damage. Efficient cooling prolongs tool life and maintains material integrity.
Peck Drilling Technique
For deeper or layered composite materials, intermittent peck drilling cycles (drill in, retract, clear debris) help manage heat and debris evacuation, improving hole quality and preventing delamination or tool breakage.
Material-specific Considerations
- For composites, supporting fragile or thin layers with backing material prevents deformation during drilling.
- For high-temperature or metal-core PCB materials, drilling parameters must account for thermal expansion and material hardness, selecting appropriate drill types and speeds.
- For HDI or wearable device substrates, stringent control over laser drilling parameters is essential for clean, consistent microvias crucial for plating and electrical performance.
Impact on Fabrication
Improper parameters can cause delamination, microcracks, distorted holes, debris contamination, voids during copper plating, or tool wear—all decreasing yield and reliability. Conversely, optimized drilling with appropriate tool choice, speed, cooling, and peck cycles enhances hole quality, plating uniformity, and adhesion, ensuring mechanical and electrical integrity critical for high-density, flexible, or multilayer hybrid PCBs.
Rigid-Flex Cases and Other Considerations
In rigid-flex cases, "peck" drilling is used to control the machines and drill a certain distance before withdrawing the drills to let them cool. Silver tarnishes quickly, and assembly must be completed soon after board fabrication. Consulting manufacturers at the outset of a project is advised to ensure design decisions align with their capabilities and requirements.
Alternatives to Polyimide and PTFE Materials
Laminate suppliers are working to provide alternatives to polyimide and PTFE materials with manufacturing characteristics similar to FR4. Different feed and speed requirements exist for drilling various materials, such as polyimide and flex materials, which can be problematic in hybrid builds.
Surface Finishes
Immersion silver or immersion gold finishes are better alternatives for designs with tight contact pitches. Immersion silver does not require a layer of nickel underneath as does the immersion gold finish. Immersion silver is preferred if there are press-fit connectors in the design due to its ability to be held to a tighter tolerance. ENEPIG (electroless nickel, electroless palladium, immersion gold) is a more expensive surface finish with nearly universal advantages. HASL (hot-air solder leveling) surface finish is not suitable for designs involving fine-pitch components due to its unevenness. Both immersion silver and ENIG result in even surfaces that are much flatter than can be obtained with HASL.
Designing Hybrid Stack-ups
Designers should consult manufacturers before developing hybrid stack-ups, as combining laminates with dissimilar mechanical properties can complicate fabrication and affect cost. Rogers 4000 materials have drilling characteristics that are relatively close to FR4, but can still result in defects due to slower drilling and heat generation.
In summary, by carefully tailoring drilling parameters to the specific hybrid PCB materials (composites, metals, polymers), manufacturers can achieve precision, minimize thermal and mechanical stress, and support downstream processes like plating, ultimately leading to robust, high-performance PCB fabrication.
In the context of hybrid PCB manufacturing, the peck drilling technique, employed for deeper layers or composite materials, aids in managing heat and debris, ensuring hole quality and preventing delamination or tool breakage (controlled impedance). Data-and-cloud-computing technologies are essential for designers when selecting materials and optimizing drilling parameters for high-density, flexible, or multilayer hybrid PCBs, as they can help achieve precision, minimize thermal and mechanical stress, and support downstream processes like plating (technology).
