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> With a Cover layer, without PTH

> Without PTH or a Cover layer

1. Substrate Preparation

The process begins with meticulous preparation of the flexible base material, typically polyimide or polyester films. These substrates are carefully cut, cleaned, and inspected to ensure optimal surface conditions for subsequent layers.

2. Copper Deposition

Next, ultra-thin copper layers are deposited on both sides of the substrate through an electroless plating process. This critical step creates the conductive pathways for circuitry on the double sided flex PCB.

3. Photolithography

A photosensitive material is then applied and selectively exposed to UV light through a circuit pattern photomask. This step defines the precise traces and pad locations on the copper layers.

4. Etching

The exposed areas of the copper are subsequently removed through a chemical etching process, leaving behind the desired circuit pattern on both sides of the flexible substrate.

5. Hole Drilling

Precise drilling or punching is performed to create vias and other necessary holes for component mounting and layer interconnections.

6. Plating and Surface Finishes

Additional metal plating and surface finishes like ENIG, HASL or OSP are applied to enhance solderability, conductivity, and protective properties of the double sided flex PCB.

7. Solder Mask and Legend

A solder mask is carefully applied to protect the copper traces, while legends are printed for component identification and reference designators.

8. Final Assembly and Testing

The last step involves assembling components on the double sided flex PCB, followed by comprehensive electrical testing, environmental stress screening, and final quality inspection.

1. Electrical testing

Electrical testing involves applying a voltage to the circuitry and measuring the current and resistance of the traces and components. This can detect any open or short circuits, as well as other defects such as improper component values or incorrect polarity.

2. Continuity testing

Continuity testing is used to verify that there is a connection between two points in the circuit. This is typically done using a multimeter to check for resistance or voltage across the circuit.

3. Thermal testing

Thermal testing is used to determine how well the double-sided flex PCB handles heat. This can involve applying a controlled amount of heat to the board and measuring the temperature, or exposing the board to a temperature chamber to simulate the conditions it will be exposed to in its intended application.

4. Vibration testing

Vibration testing involves subjecting the double-sided flex PCB to mechanical vibrations to simulate the conditions it will be exposed to during use. This can detect any weak or damaged areas in the circuitry or components.

5. Flex testing

Flex testing involves bending or flexing the double-sided flex PCB to test its durability and resistance to mechanical stress. This can be done manually or using a specialized testing machine that applies controlled amounts of stress to the board.

6. Environmental testing

Environmental testing involves exposing the double-sided flex PCB to different environmental conditions such as temperature, humidity, or chemicals to test its resistance to these conditions. This can help detect any weaknesses in the circuitry or components that may affect performance or reliability.