What are the trends in Consumer Electronic Products assembl
2018-11-25 16:35Writer: qyadminReading:
The essential property of consumer electronic products lies in their miniaturization and diversification. Due to the leading two trends, assembly technologies applied by consumer electronic products become increasingly complex, arousing more significance in assembly process control. With the development of diversification and constantly shortening lifecycle, invest time shortening, fast turnaround, flow manufacturing and rapid production are called for.
This article will discuss assembly development trend of consumer electronics from perspectives of components, substrate and assembly technologies.
Integrated Circuits (ICs) Development
The primary development of components serving for consumer electronic products is miniaturization and integration. As far as IC is concerned, miniaturization can be achieved through the applications of bumps (usually eutectic solder) to replace leads for the implementation of interconnection. Although bumps can be an excellent alternative for leads for the sake of space saving, space saving becomes limited for BGA (ball grid array) with a pitch of 0.8mm or more. Space can never be best used unless CSP (chip-scale package) with a pitch of 0.4mm at most is leveraged. Lots of modern consumer electronic products nowadays depend on CSP with miniaturization achieved including portable products, wearables etc.
CSP can be classified into five categories:
• Rigid substrate-based CSP
• Flexible substrate-based CSP
• Customized leadframe-based CSP (LFCSP)
• Wafer-level redistribution CSP (WLCSP)
• Flip-chip CSP (FCCSP)
WLCSP receives the most interest as far as miniaturization is concerned. It is formed before it is cut into wafer, which leads to the result that the package size is smaller than that of wafer. Most WLCSPs redistribute pads on wafer and plant solder balls. They can be regarded as a type of flip chips.
The reliability of WLCSPs is most concerned especially when they are ready to be assembled on FR4 substrate board. Because silicon and PCB (printed circuit board) share different CTE (co-efficient of thermal expansion), the size of the largest wafer receives limitations. As a result, WLCSP is mainly used on ICs with a small number of pins.
When ICs with a large number of pins call for miniaturization on height, flip chip technology has to be relied on. As a matter of fact, difference becomes increasingly vague between flip chip and WLCSP. The former features smaller pitch that is usually in the range from 100μm to 150μm.
Compared with packages with lead pins, QFP (quad flat package) for example, BGA and CSP feature higher cost. Furthermore, much higher cost has to be confronted for that of substrate board because multiple layers and mircrovias are often required as far as I/O interconnection is concerned.
The leading disadvantage of WLCSP and flip chip lies in their non-standardization on their size. Package size is equivalent with that of wafer so that package can have any size. To prohibit demands for customized test socket, tray and foil, it's best to implement multiple operations in WLCSP.
Development Trend of Passive and Discrete Devices
The smallest passive component is 01005 (0.4*0.2mm). Another method to reduce the size of passive components is to integrate it on silicon chip or glass.
Some components like transistors can be also packaged into WLCSP. Redistribution can be carried out on the front side of wafer through plating on via in silicon chip or groove. Silicon chip and groove can be generated through laser drilling whose disadvantage is to possibly cause debris.
The third method to reduce the size passive components is to integrate it into substrate which will be discussed in later part of this article.
Module application is a potential development trend that integrates ICs and passive components on wire plugging layer and then assembles or connects it onto substrate board. When it comes to high-frequency modules or high energy consumption applications, ceramic substrate is applied.
A couple of methods can be used to plant solder balls on BGA, CSP, flip chips and modules among which the lowest cost method is to manufacture solder balls by printing solder paste through stencil. Next, reflow soldering is implemented with flux cleaned off. To obtain better cleaning effect, water washable solder paste is usually applied. Printing method is capable of achieving maximum bump size, mainly depending on the following aspects:
• Sufficient space should be left to be compatible with stencil opening.
• Stencil thickness
• Metal ingredient of solder paste
• Defects presence such as bridging
Development Trend of Substrate Board
Due to leading development trend of consumer electronics products, that is, miniaturization and diversification, traditional rigid multi-layer PCBs will be constantly replaced by rigid microvia multi-layer PCBs and flexible PCBs. Furthermore, more PCBs are used as wire plugging layers for BGAs and CSPs.
Besides, passive component embedded into substrate board is another development trend for substrate. This type of substrates can save more space and holds better electrical functions, also suitable for the integration of capacitors, resistors and inductors.
Development Trend of Soldering Technology
The miniaturization trend of components calls for higher requirement of soldering technology.
Based on chip size of flip chips and WLCSP, it's necessary to meet the requirement of high reliability by filling solder at the bottom. When viscous flux is used for flip chip interconnection, viscous flux type will affect the performance of bottom filling solder.
Development Trend of Environmental Protection Awareness
Environmental protection starts playing a significant role to consider in electronic assembly. Nowadays, design focuses on both assembly and decomposition so that materials can be reused again.
To stop lead from polluting the environment, lead-free solder paste has to be used. Up to now, lead free and green have become an essential consideration for electronics manufacturers.
Apart from lead-free solder paste, lead-free coating material and component coating material should be used as well. All the lead-free solder paste, PCBs and components coating material should not only be evaluated from technology and their influence on environment has to be carefully considered and figured out. From the perspective of manufacturing, temporary lead-free alloy is optimal. But compared with lead solder paste, it can not be used any more if it is harmful to the environment during manufacturing, application or waste processing.