Based on structure of flexible PCB, materials contributing to flexible PCB include insulating substrate material, adhesive, metal conductor layer (copper foil) and cover layer. Primary material for flexible PCB has to be flexible insulating film that plays a role as a carrier with excellent mechanical and electrical performance. Ordinary materials include polyester and polyimide film and the latter is used in majority. Along with research and development of new materials, selective materials become so diversified that other types of substrate materials are available like PEN and thin FR4 apart from the ordinary materials.
What are the assembly properties of flexible PCB?
From Flexible PCB to Rigid PCB
Flexible PCB tends to get deformed due to its light weight and thinness, incapable of being directly assembled on SMT manufacturing line like rigid PCB. Thus, to successfully implement assembly on flexible PCB, it has to be fixed on rigid carrier or tray so that it can be dealt with like rigid PCB. Flatness, accuracy of positioning and consistency of board carrier play a key role in completing product quality, which is where flexible PCB assembly focuses on.
Up to now, because flexible PCB features higher cost than rigid PCB, majority of flexible PCBs are only applied for connections between modules with different functions based on product cost concern. As a result, the number of components ready to be assembled on flexible PCB is relatively low with low assembly density. Generally speaking, the number of components is within 50 and some boards contain only two connectors.
Large Number of Panels
Flexible PCB is mainly used in miniaturized electronic products such as cell phones and digital cameras so that the area of single board is small. Furthermore, the number of components assembled on single board is quite low, so in order to improve assembly efficiency, panels are usually applied for assembly after which they will be separated through punching.
Wide Applications of Auxiliary fixtures during Assembly Process
Lots of auxiliary fixtures participate in flexible PCB assembly due to its deformation and damage features, including flexible PCB baking fixture, board carrying tray, electrical test fixtures, function test fixtures and cutting fixtures.
High Requirement on Product Quality
Since flexible PCB is usually applied in the environment calling for repeating bending and control accuracy, components assembled on flexible PCB have to be able to meet the demands of their application environment. As a result, flexible PCB calls for higher requirement in terms of cleanliness, anti-static precautions and soldering reliability than rigid PCB. In addition, owing to prevalence and acceptance of lead-free manufacturing technologies, flexible PCB assembly has to face up with some technical challenges.
High Assembly Cost
Compared with rigid PCB assembly, flexible PCB assembly leads to a high overall cost, which is especially true in the starting phase. As a result of wide range of applications of fixtures, long manufacturing period, low rate of equipment utilization, higher demands of accessories and staff and higher requirement on manufacturing environment and product quality.