Circuits Assembly - December 2007 - (Page 22)

COB for SMT Metalization Options for COB Assembly Mukul Luthra Traditional boundaries of backend process and SMT assembly have become diffused. Ed.: For the complete article, visit circuitsassembly.com/cms/ content/view/5773. all within the package itself. Other than the final overmold and ball attach, if applicable, the process replicates the COB-SMT concept as deployed for mainstream surface mount assembly. Metalization and Product Positioning Figures 7 to 12 show several diverse applications of COB-SMT. Figure 7 is an assembly from a handheld toy fan with motion activated flashing lights. It uses a single-sided BT resin PCB with OSP over copper pads and nickel over copper bond pad metalization. At the next price point, Figure 9 shows the COB in a PDA using a multilayer FR-4 PCB with uniform nickel metalization at both soldering and wire bond sites with AlSi wire bonding process. Figure 10 is the display and control module from a microwave oven and Figure 11 shows the main and remote control assemblies from a mini-disk player. Both products use ENIG pads for both soldering and wire bonding. Figure 12 is the assembly from a high-end heart rate monitor using ENIG at the solder sites and selectively plated soft pure gold at the COB sites. The common factor in each of the shown products is COB, yet metalization choices are dictated by product positioning, life, reliability expectation and price point. The cost-sensitive low end uses metalization that leans in favor of the soldering process. Conclusion Wire bonding is not out of steam, given improvements in the latest generation of circuitsassembly.com ithin mainstream surface mount assembly, bare die wire bonding directly to the PCB substrate and adjacent to other soldered components has long been practiced for low end to high performance assemblies. The backend IC industry, with its decades of understanding wire bonding metallurgy, finds itself acquiring and adapting SMT know-how to the field of packaging. The surface mount industry, however, may find it relatively harder to deal with the complexities of wire bonding. This article reviews metalization options and interactions for COB, while considering needs of the bonding process and soldering. Apart from size and footprint advantages, organic-based packaging offers a significant spinoff: It is a platform readily adaptable by the IC backend toward attaching multiple dies and other active and passive components on a substrate within an IC (BGA or CSP). After overmolding, the resulting assembly creates a highly functional device. Systems-in-package (SiPs) and multichip modules are two examples. Thus, after decades of packaging – typically – a single die on a metal lead frame, the face of IC backend is being permanently transformed and acquiring the flavor of a PCB assembly-like process, albeit one involving dies and surface mount W 22 Circuits Assembly DECEMBER 2007 http://www.circuitsassembly.com/cms/content/view/5773 http://www.circuitsassembly.com/cms/content/view/5773 http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - December 2007

Circuits Assembly - December 2007 Contents Caveat Lector Industry News Market Watch Talking Heads Global Sourcing Screen Printing Better Manufacturing Metalization Options for COB Assembly A Test Comparison of SAC and Non-SAC Pb-Free Solders An A-to-Z Guide to X-Ray Inspection BEST: A ‘Funky Chicken’ with an EMS Niche Tech Tips Wave Soldering Process Doctor Pb-Free Lessons Learned Getting Lean Eastern Approaches Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - December 2007

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