Introduction

Copper clad laminate (CCL) forms the basic structure of printed circuit boards. CCL consists of a central insulating core material sandwiched between layers of copper foil. The manufacturing process to create quality CCL utilizing epoxy resin involves multiple steps including impregnation, lamination, copper bonding, and final finishing. This article will overview the end-to-end CCL production process using epoxy resin chemistry.

Overview of CCL with Epoxy Resin

CCL material consists of:

• Central insulating dielectric core
• Layer of copper foil on each side
• Epoxy resin throughout core

The core provides mechanical support. Epoxy resin gives chemical adhesion and bond integrity. Copper foil enables circuit patterning.

Epoxy resin CCL offers:

• High bond strength
• Good thermal performance
• Excellent chemical resistance
• Long-term reliability
• Cost effective manufacturing

Epoxy resins are the most common resin system used in PCB materials.

CCL Manufacturing Steps

Producing quality CCL with epoxy resin involves the following key steps:

1. Core Material Preparation

The insulating core material comes in sheets consisting of woven fiberglass cloth. The material is inspected, cleaned, batched, and staged for impregnation.

2. Resin Mixing

Liquid epoxy resin is weighed and mixed with hardeners and other reactive additives to form the impregnation resin. The mix is filtered for cleanliness.

3. Impregnation

The core material is pulled through a tank of prepared resin. The woven glass cloth fully wets out as resin penetrates evenly throughout each sheet. This stage determines final resin content.

4. B-Stage Oven Curing

The impregnated core material is pulled through a long heated tunnel oven. Heat causes partial curing of the resin into a tacky B-stage state ready for lamination.

5. Copper Foil Bonding

Rolls of thin copper foil are pressed onto both sides of the impregnated, B-stage core material. The assembly then enters a heated nip roller press.

6. Autoclave Lamination

The copper clad sheet enters an autoclave chamber. High pressure and heat fully cures the resin bonding the foil to the core into a solid laminate.

7. Cooling

After autoclave curing, the laminate passes through a cooling zone to bring CCL temperature back down for additional processing.

8. Roller Treatment

Roller presses apply mechanical pressure to ensure lamination uniformity, remove any air pockets, and improve surface smoothness.

9. Machining

Computer numeric control (CNC) routers machine the CCL into standardized sheet sizes with beveled edges. Holes may also be drilled.

10. Quality Inspection

100% inspection of CCL sheets checks for defects, thickness, hole quality, and other metrics to ensure specifications are met.

11. Packaging

Inspected sheets are carefully packaged to avoid damage prior to shipment or further PCB processing.

The CCL sheets must meet exacting standards to endure PCB fabrication, assembly, and service life. Strict process controls provide consistent, high-quality CCL product.

Key Process Considerations

Several factors are critical during CCL manufacture:

Resin Content

The amount of resin solids impregnated into the woven glass must stay within a target range. Too much or too little resin impacts properties.

No Voids

Air pockets between glass fibers or delaminations create weak points that can cause PCB failures.

Controlled Thickness

Consistent core thickness is critical across each CCL lot. Thickness uniformity impacts subsequent PCB processes.

Bond Integrity

Strong, uniform bonds between resin, foil, and glass withstand PCB processing stresses and temperature cycling.

Dimensional Stability

Sheets must exhibit minimal curling or shrinking to avoid registration issues during PCB imaging and etching.

Cleanliness

No residue or foreign material can remain on surfaces or in the core to prevent PCB defects.

Maintaining strict tolerances and disciplines for these parameters ensures reliable CCL quality.

Material Options

Various material options exist when formulating CCL with epoxy resin:

Epoxy Chemistry

• Standard Bisphenol A epoxy
• High Tg epoxy for improved thermal capability
• Halogen-free epoxy for environmental compliance
• Low Dk epoxies to reduce signal loss

Core Material

• Standard E-glass with greater resin absorption
• Quartz glass that absorbs less resin
• Non-woven aramid or polyester fibers

Copper Foil

• Standard ED copper
• Rolled annealed copper for high ductility
• Low profile copper foils

Coatings – Treatments can be applied to finished CCL sheets:

• Oxide surface treatments to improve resin bonding
• Graphite coatings to reduce drilling debris

The choices result in application-specific CCL material optimized for electrical, thermal, and mechanical needs.

Quality Control Testing

To validate material performance, CCL undergoes extensive quality control testing at multiple stages:

• Interlaminar Bond Testing – Measures resin-to-foil peel strength
• Microsection Analysis – Checks layer uniformity under magnification
• Thermal Stress Testing – Evaluates degradation under temperature cycling
• Fabrication Simulation – Test drilling, imaging, and etching on samples
• Dielectric Analysis – Determines dielectric constant and loss tangent
• Dimensional Stability Analysis – Quantifies shrinkage and expansion
• Electrical Testing – Verifies dielectric breakdown voltage

Statistical process control with extensive testing provides the assurance of product quality and consistency.

Conclusion

Manufacturing reliable copper clad laminate utilizing epoxy resin requires careful process control and validation. When executed properly, CCL provides the robust foundation needed for further PCB fabrication and assembly into quality electronic products. The combination of high performance resins, sturdy core materials, and advanced manufacturing techniques enables CCL to serve its vital role in the production of printed circuit boards.

Frequently Asked Questions

Q: Why is fiberglass most commonly used as the core material in CCL?

Fiberglass provides an optimal balance of mechanical strength, dimensional stability across temperature variations, dielectric performance, and cost-effectiveness. The woven glass cloth construction also absorbs resin effectively during impregnation.

Q: What are some key advantages of epoxy resin systems?

Epoxy resins offer high adhesive strength, chemical and moisture resistance, good dielectric properties, processing versatility, and cost efficiency. These characteristics make epoxies ideal for electrical applications.

Q: What is the difference between FR-4 and other common CCL designations?

FR-4 is a specific flame-retardant grade of CCL made from brominated epoxy resin and E-glass core. Other grades like G-10 and FR-5 indicate different resin systems, core materials, and characteristics optimized for specific applications.

Q: How does CCL thickness tolerance impact PCB manufacturing?

Consistent CCL thickness is critical for maintaining registration during layer-to-layer imaging and etching processes in PCB fabrication. Tighter thickness tolerances enable higher density PCB technologies.

Q: What is the purpose of beveled edges on CCL sheets?

Beveled edges prevent sharp corners from damaging handling equipment or operators. The angled edges also help avoid peeling or lifting during inner layer lamination in multilayer PCB fabrication.