Surface-mount technology reliability

Microfluidic Boards Microfluidic board interconnection technologies seek to mimic the electronic printed circuit board for ease of use, reliability, and versatility. In microfluidic board technologies, the substrate contains the passive microfluidic channels and reservoirs, with active components (e.g., sensors, valves) mounted on top (e.g.. Ref. [2]) (see Fig. 1) similarly to electronic components mounted on a printed circuit board (PCB) or multichip modules (MCM) in surface-mount technologies (SMT). Electronic coimections between components are provided on top of the board, while fluidic interconnection is usually provided in the board material itself. Microfluidic circuit boards can be made from a variety of materials, including silicon, glass, and polymers, e.g., polydimethylsiloxane (PDMS), epoxy, or polymethyl methacrylate (PMMA). Microfluidic boards can be as simple... 

In surface mount technology, the components are soldered directly to the surface of a PWB, as opposed to thro ugh-hole mounting. This allows efficient use of board real estate, resulting in smaller boards and simpler assembly. Significant improvement in electrical performance is possible with the reduced package parasitics and the short interconnections. However, the reliability of the solder joint is a concern if there are CTE mismatches (Seraphim et al, 1989). 

Britt, L., The Use of Commercial Components in a High Reliability Environment, Surface Mount Technology (Nov. 2000)... 

Turbini, L. X, Bent, W. R., and Ready, W. X, Impact of Higher Melting Lead-Free Solders on Reliability of Printed Wiring Assemblies, Journal of Surface Mount Technology, Vol. 13, No. 4,2000, pp. 10-14. 

IPC-D-279, Design Guidelines for Reliable Surface Mount Technology Printed Board Assemblies, to be published. 

For a more comprehensive list of components that may be at risk, see IPC-D-279, Design Guidelines for Reliable Surface Mount Technology Printed Board Assemblies, App. C, to be issued. 

Electronic packages are composed of complex materials that are assembled via intricate processes and then subjected to a wide range of service environments. It is crucial to note that both the die-packaging processes and surface-mount technologies can impart stresses and create residual stresses in the final packaged assembly that impacts its interconnect reliability. Assessing the rehabihty of package devices requires that all variables that can hinder or enhance reliabihty be considered. 

IPC-D-279 Reliability Design Guidelines for Surface Mount Technology Printed Board... 

The development of surface-mounted technology (SMT) using surface-mounted devices (SMD) was a major development. SMD are active and passive electronics components without conventional connecting wires. SMD components can be placed on the solder side of the PCB and their metal caps soldered to the copper pads of the PCB. Both layers of the PCB can therefore be used as active areas. The SMT technique opened advantages and new applications through miniaturisation of components and increased reliability. 

Turbini, L.J. Bent, W.R. Ready, W.J. Impact of higher melting lead-free solders on reliability of printed wiring assemblies. Journal of Surface Mount Technology 2000, 13, 10 14. 

Pricing as well as reliability considerations have led to an almost exclusive use of Si-based (i.e. Si and SOI) micro machined devices. Packaging and assembly has focused on ceramics (A1203, AIN, Low Temperature Co-fired Ceramics LTCC), Printed Circuit Board (PCB-) and Surface Mount Device (SMD-) technology and multichip modules (MCM s). 

Besides die attachment, ICAs are utilized in surface mount and flip-chip packages as alternatives to traditional solders. Due to their low surface tensions, ICAs are not suitable for wave soldering (Ref 6). Despite the advantages of ICA interconnection, the wide use of this technology has not been adopted by the electronics industry. The main concern is long-term reliability. 

R.S. Rorgren and J. Liu, Reliability Assessment of Isotropically Conductive Adhesive Joints in Surface-Mount Applications, IEEE Transactions on Components Packaging and Manufacturing Technology, Part B, Vol 18, 1995,p 305-312... 

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