Flexible circuits PCB have become functionally pivotal and a fast growing electronic goods technology. These circuits function as connectors in most applications where space saving, construction constraints and flexibility limit service capability of hand wiring or rigid circuit boards. The substrate that is used in LCD fabrications is glass. If thin, a flexible metal or plastic foil functions as a substrate. Since there is a very thin film deposit on top of the substrate, the entire system is usually very flexible. To ensure flexible displays, organic light-emitting diodes are used. These make a flexible display.

Lead-free circuits 

The use of lead-free circuits has been increasingly steadily over the years. The medical industry was among the first sectors to go lead-free completely since the adoption of the RoHS directive by the electronics industry in 2006. Today, a large percentage of circuits assembling and soldering is done using lead-free materials. After many years of withstanding mischaracterizations and refinement, lead-free circuits are proving to be reliable and cost-effective.

Lead-free flexible circuit assembly

Lead-free flexible printed circuits assembly on a plastic substrate is commonly used in different electronic appliances. Although different components can be used to assemble these circuits including polyimide or polyester, PCP manufacturers mostly use lead-free soldering alloys for mass production.

flexible PCB assembly

Here are the steps of the assembly process:

Step 1: Temporarily assembly of the components 

The first step is to assemble a flexible PCB with reflow soldering or wave. This entails arranging electronic components and keeping them in their right place temporarily using adhesives.

Step 2: Pins location for flexibility 

Sprung pallets locations and fixed pins are used to enhance flexibility. The protrusions of the used pins should be about 0.010” above the circuit.

Step 3: Set the pallet base 

The used pallet base in Surface Mount Technology PCB assembly should have areas for thermal relief. These areas assist in enhancing delta T during lead-free solder alloy reflow. If you intend to use vapor phase for reflow, consider drain holes under your flex.

Step 4: Print the paste of a lead-free solder 

Recess a 0.006” stencil on the foil base to allow for pallet clips protrusion. The stencil should be recessed by 0.003”.Two different sizes of the apertures on three different electronic components footprints should be used in printing the solder paste. To enhance efficiency in the assembly process, recesses should be placed around the protrusions of the pin from the pallet.

Step 5: Heating the assembly 

The flexible PCB assembly is heated by passing it through a controlled, preheated oven or with a hot air pencil. An infrared lamp can also be used. Heating fixes the soldered parts of the lead-free circuit in place.

Applications of lead-free flexible circuits 

Flexible lead-free circuits are used in a wide range of electronic appliances including cell phones, microwaves, computer panels and cameras. Majority of these circuits form passive wiring that is used in interconnecting electronic components like capacitors, resistors and integrated circuits. In automotive, these circuits are used in under-hood controls and apparatus panels. They are also used in computer peripherals like print heads of printers. In the medical field, they are used in medical devices where different interconnections are required in compacted packages.

Generally, lead-free flexible circuits assembly requires technical knowledge to ensure that the final product conforms to the preferred shape and that it flexes during its use.