A flexible printed circuit board (FPC) that is thin, flexible, and bendable. Even though it is the same printed circuit board, the materials, and characteristics are different from those of a hard rigid circuit board. Can component mounting technology and connection technology for rigid boards be used for flexible boards?
Mounting of chip parts
- Apply cream solder
A blank raw board and a metal mask (stencil) are overlaid, and cream solder (solder paste) is applied.
Equipment used: Creams solder applicator - Mount chip parts
Chip parts are mounted on the front side (A side) or the back side (B side) of the printed circuit board. The size of parts that can be mounted differs depending on the equipment.
Equipment used: chip mounter - Soldering
Melt cream solder and solder the board and chip parts.
Equipment used: reflow furnace - Inspection
Check for defects. Inspection equipment that uses image analysis can automatically detect even small defects.
Equipment used: Image inspection equipment
Mounting lead parts
1. Mount lead parts
Mount radial/axial components (components with leads) on the surface (side A) of the printed circuit board. By using an automatic insertion machine, it is possible to mount the taped parts to the specified position.
Equipment used: Automatic insertion machine
2. Mount lead parts
Parts that cannot be inserted by an automatic insertion machine are mounted by hand. It is also called manual insertion. Heavy parts such as relays cannot be mounted by machines. Although mechanization is progressing, there are still many parts mounted by manual insertion. Since it is done manually, the skills of skilled workers are required to maintain quality.
3. Soldering
Flux is applied to pre-soldering printed circuit boards. Applying it to the back side of the printed circuit board improves solder adhesion.
Equipment used: Fluxer
After applying flux, solder the board and lead parts.
Equipment used: flow solder bath
4. Inspection
Inspect for defects.
Equipment used: Image inspection device
*If there are backing parts, they will be soldered by hand.
Mounting technology for rigid boards can also be used for flexible boards
Various component mounting technologies and connection technologies have been put into practical use for rigid boards, but most of them can also be applied to flexible boards. However, it is not as it is, and some ingenuity and condition setting is required.
Load retention by reinforcing plate
The base material of flexible substrates is a thin film. Since the mechanical strength is weaker than that of a rigid board, a reinforcing plate is attached around the mounting area to make it harder. As a matter of course, the reinforcing plate is attached on the opposite side to the soldering.
When mounting relatively large and heavy parts such as lead parts, a material with high mechanical strength such as glass epoxy is used as the reinforcing plate. Don’t forget to make a component insertion hole in the reinforcing plate itself.
A thick polyimide film is sufficient as a reinforcing plate when mounting small and light surface mount components. Since it is a surface mount component, there is no need to insert a component insertion hole in the reinforcing plate.
COB (Chip on Board)
Rigid substrates are widely used for mounting semiconductor chips directly on the substrate, but flexible substrates can also be applied in the same way if appropriate process conditions are selected.
Specifically, it is a joining technology such as wire bonding. Since the base is soft, it is necessary to adjust the bonding conditions and reinforce the back side of the board.
Soldering
Flexible substrates have lower heat resistance than rigid substrates, so proper consideration is required in high-temperature processes such as soldering.
Polyimide film, which is commonly used for flexible substrates, has high hygroscopicity, and if it is placed in a high-temperature process such as a solder bath, the moisture will evaporate, which may cause peeling of the conductor or overlay.
Connector
Various connectors have been developed and put into practical use for rigid boards. If you attach a reinforcing plate to the back side of the flexible board and adjust the thickness, you can use it by inserting it into those connectors without making any major changes. Incidentally, most card edge connectors assume a printed circuit board thickness of 1.6 mm.
Points for choosing an outsourcing manufacturer
As electronic components continue to become smaller and denser, it is important to have production facilities in place.
Manufacturers that have introduced a lot of equipment are also attractive, but the cost varies depending on the mounting method, so it is important to carefully listen to the performance you want to achieve and the parts you want to use, and then select the manufacturer that can make the best proposal. It’s recommended.
In addition, each manufacturer specializes in different fields, and some manufacturers are good at mass production and low-volume, high-mix production of pcb board.
Summary
So far, we have introduced board mounting. A high-quality control board is completed by accumulating each process. If you are considering outsourcing, why not consider what kind of machines is installed, whether there are skilled workers, and whether the proposal for the mounting method is kind.