Adhesive-free materials have become a popular option for use in flex circuits. Without an adhesive layer, the entire product can be thinner and more flexible. It’s also easier to manufacture flex circuits using different techniques when no adhesive layer exists. Best of all, adhesiveless materials tend to have better electrical properties.

We can manufacture adhesiveless flex circuits is two different ways:

• Cast dielectric

Starting with .5-, 1- or 2-ounce copper and a thin layer of polyimide, cast dielectric materials are cast onto the circuit surface. It’s available with copper on a single side or both sides of .001 inch or .002 inch polyimide.

• Sputtered Cu

Sputtered materials start off with polyimide film at .001 or .002 inches. We sputter angstrom thick copper over a chrome, no-chrome, or monel barrier layer. More copper is plated to a thickness of 200 microinches. These materials provide the unique advantage of being able to be used for manufacturing semi-additive circuits.

Adhesive-based materials are made using a layer of adhesive between the polyimide film and copper layers within the flex circuit. This creates a reliable mechanical bond. Tech-Etch uses acrylic and epoxy adhesives, depending on the requirements of our clients. We also offer other adhesives if needed.

• Rigid-flex substrates

We use flex materials and rigid laminate materials to create our rigid-flex products. Our laminates are usually FR-4 bonded with epoxy pre-preg. We can work with materials sourced from a variety of manufacturers.

• Alternative circuit layer materials

Tech-Etch’s experience in photo etching gives us the ability to use a wide variety of conductor materials for the job. From copper alloys and nickel to Kovar and stainless steel, we can do it all.

When it comes to cover layer materials, the standard is polyimide film that’s bonded over the conductor layer with acrylic or epoxy. Our polyimide ranges from .0005 inches to .005 inches and is available in .001 inch increments. The adhesive thickness is a function of the construction of the circuits and is usually left to the manufacturer’s discretion.

Photo Imageable Coverlayer (PIC) is an option when your product requires high-density access to circuit layers. This is common among today’s high-density SMT designs. The material is coated over the conductors and doesn’t require adhesion of any kind. Although it’s not as resilient as polyimide film, it’s better for supporting very small and dense access openings. PIC can be tinted amber or green for easy identification.

Rigid-flex outer layers are coated with soldermark. With this make, the parts can control the flow of solder during assembly. On rigid sections, the vias are typically left open, with the mask pulled back. This is the most inexpensive manufacturing method. If the sodlermask is required to tent over the vias, there are techniques that allow for it.

Stiffeners can add rigidity where needed on your circuits. They can be added to specific areas of a circuit to strain-relieve component attachment locations, offer a firm mounting surface, or increase thickness to correspond with mechanical specifications.

When you need additional thickness between .002 inches and .009 inches, we use polyimide film to get the job done. This material can add coincidental edges to the circuit outline.

Cirlex® is another option for adding rigidity. FR-4 is used when a thickness greater than .010 is required. The features of the stiffener are typically smaller than the corresponding circuit features by .015 inches.

In addition, other metals or molded plastic can also be used for stiffness. Pressure-sensitive adhesives or standard flex circuit adhesives can be used to attach these stiffeners.