Miniaturization and multiple functions development trend of electronic products definitely push PCB (printed circuit board) manufacturing technology making progress towards high density, high accuracy, miniaturization and high speed. Because flexible PCB depends on substrate material with flexibility and is capable of being bent, which leads flexible PCB to be in light weight and small volume, recent years has witnessed its increasingly more applications in electronic products. Along with the constant improvement in terms of flexible PCB manufacturing technology, advanced PCBs such as flex-rigid PCB and HDI (high density interconnect) flexible PCB are making rapid progress on their fabrication technologies as well.
Furthermore, the rising and flourishing of intelligent terminal electronics like smart phones and tablet PCs have also seen obvious demand growth for flexible PCB, flex-rigid PCB and HDI PCB. It can be forseen that flexible PCB will become a hot spot as far as PCB industry is concerned. Development of PCB boards is closely correlated with the development of material and technologies, so this article will discuss development opportunities and challenges flexible PCB has to face up with in terms of new material and new technologies and will talk about development trend of flex-rigid PCB.
Development Trend of New Materials and New Technologies
Innovation of flexible PCB largely depends on the growth of new materials. Material innovation occurring to insulating substrate material, adhesive, metal foil, cover layer and strengthening board all drives circuit boards to embrace higher performance. Because flexible PCB fabrication calls for higher requirement on all kinds of materials, diversified material systems will provide multiple selections and combinations for manufacturers. Material performance primarily comes in CTE (coefficient of thermal expansion), water absorption, flexibility extent and flexibility lifespan.
In PCB industry, new materials and new technologies usually help each other forward, which works perfectly on flexible PCB owing to its higher requirement on its performance. For example, as one of core technologies for PCB innovation, microvia fabrication technology moves at a higher speed than any other technology including etching, plating and connection. During the fabrication process of microvia in flexible PCB, mechanical intensity and deformation coefficient of different materials on different layers should be carefully considered and deformation should be estimated as a result of via manufacturing. In the end, accurate microvia will be successfully manufactured.
Since flexible PCB technology takes advantage of flexible substrate material, it is compatible and complementary to printed electronics technology that becomes prevalent in recent years. Thus, how to make use of printing technology in additive process to manufacture circuit boards is a new topic flexible PCB industry should focus on. Therefore, rigorous demands are laid to compatibility between PCB material and PCB fabrication technology and ink and substrate material for the use of printed electronics.
Progress on materials and technologies can further get flexible PCB application range expanded. For example, LED PCB playing a leading role in current market depends on the design of rigid board plus metal backplane. As heat-resistant quality of material becomes optimized, flexible PCB will be applied in thin and light LED products. Another remarkable application of flexible circuit board lies in automotive PCB. Up to now, automotive electrical part primarily takes advantage of wire connection and equivalent thin flexible PCB is lighter by 70% than wires. Breakthrough in high polymer material R&D improves high-temperature stable working range from current 100°C to 125°C to 200°C or higher. In addition to high-efficient and excellent electric induction and control performance, flexible PCB will be more applied in automotives and play a key role.
Development Trend of Flex-Rigid PCB
Thanks to combined advantages of both flexible board and rigid board, flex-rigid PCB has been widely applied in electronic products. Development issues discussed in previous part of this article concerning flexible PCB are equivalently applicable for flex-rigid PCB fabrication technology. Moreover, since more material differences are concerned in flex-rigid PCB, all the technical challenges mostly derive from material combination selection. For instance, during multiple lamination process, CTE difference on all directions of each layer of material should be carefully considered together with the application of reinforcing board so that deformation compensation can be implemented with high-accuracy alignment lamination achieved.
Meanwhile, structural design of flex-rigid PCB is also a hot spot for its development. Generally speaking, flex-rigid PCB with equivalent functions perhaps features numerous design schemes. Practical design should start from comprehensive considerations including products' reliability, occupied space, weight and assembly complexity. Furthermore, manufacturers' manufacturing capability and material elements should be taken into consideration for optimal design with the program with the lowest picked up. For example, ordinary 3-layer to 8-layer flex-rigid PCB may take advantage of flexible CCL (copper clad laminate) with adhesion used or unused. Similarly, cover layer of flexible area in flex-rigid PCB features different structures.
Another research development trend of flex-rigid PCB lies in component embedded PCB fabrication. In most situations, resistor and capacitor embedment is required to be carried out in rigid area without flexible area performance affected. This application lays rigorous requirement to material for a second time. Furthermore, flexible PCB works suitably on CSP (chip-scale package) technology and component embedded PCB structure brings forward challenges and requirement for packaging technology.
Future Expectations for Flexible PCB
Flexible PCB will develop towards ultra-thinness and high density, which will arouse further progress in terms of material, technology and equipment with new technologies encouraged. It can be forseen that flexible PCB development will center on the following aspects in future short or long term:
• Thinner and lighter PCB structure;
• Higher data processing speed;
• Higher working temperature;
• Higher density and multiple functions;
• Larger-area and more flexibility-resistant PCB;
• Component embedment;
• Circuit and light path hybrid board;
• Printed electronics compatible.
With opportunities provided, all the application expectations bring forward extreme challenges in terms of PCB material, technology and design. Therefore, sticking to technical innovation and self R&D is a must-have principle when we would like to go far in PCB industry.
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