Assembly Line Optimization

“Zero Tolerance For Defects”

Author: Robert Alexander Gray

Abstract: This paper explains the zero defects philosophy through its relevance to a typical high-volume SMT line. It assesses the cost of quality by establishing a cost model for defects in SMT assembly. It bases these cost calculations on typical industry benchmarks and what could be regarded as best-in-class. Using these benchmarks and cost model, it explains how a zero defects approach could provide a significant financial and strategic advantage. Described is one approach to a zero tolerance for defects manufacturing system for process control and optimization, with explanations of the phases and stages a process goes through as it is assessed and optimized. Practical examples of the results are presented, along with the cost of quality calculation used to validate the energy and resources required for the adoption of such an approach. (SMTA International, August 2008)

Package Reliability

“Using Strain Gauge Analysis to Optimize the PCB Design and Minimize the Risk of Component Damage During Assembly Depanelization”

Authors: Mark Logterman, Anthony Burton, Mudasir Ahmad and Lavanya Gopalakrishnan

Abstract: Assembly is commonly done on PCBs with multiple boards per panel to minimize costs in both the PWB fabrication process (optimize material costs, minimize tooling requirements, maximize throughput), as well as the assembly process (minimize tooling requirements, maximize throughput). When assembly is complete, panels are then singulated into individual boards using a variety of depanelization processes, such as a router, pizza cutter, custom breakaway jig, nibbler, and even by hand. Each process subjects the assembly to strain that potentially can cause damage to the PCB or assembled components. Strain-related component damage can begin as micro-cracks on components (i.e., ceramic chip capacitors) or solder joints (such as BGA balls) that may not be caught during product testing, but manifest themselves as latent failures in the field. To eliminate this problem, it is critical to understand the stresses applied during the board singulation process in order to optimize the PCB panel design and select the appropriate depanelization process for an assembly. (SMTA International, August 2008)

“Effects of Thermal and Mechanical Fatigue on Organic SAC 305 FC-PBGA Packages”

Author: Arv Sinha; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: Studies related to the thermal and mechanical cyclic fatigue loading were performed on a flip-chip plastic ball grid array (FC-PBGA). SAC 305 joint reliability was evaluated using accelerated thermal cycling and mechanical fatigue experiments. Effects of creep with 10 min. dwell time on heating and cooling cycles were demonstrated. The test results showed the outer row solder joints may fail earlier than any other solder joints for ATC, while a combination of outermost corner and middle solder balls failure are seen for mechanical fatigue samples. This confirms both experimental and modeling observations in the literature that the FC-PBGA solder joint failure is mainly caused by the thermally induced warpage of organic-based package for ATC. (SMTA International, August 2008)

Solder Joint Reliability

“Another Look at Lead-Free Solder Joint Reliability under Random Vibration”

Authors: Stephen Bracht, Aghavni Ball and Lisa Salerno; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: The objective of this study was to determine the effects of vibration environments on already stressed (salt atmosphere) PCB boards, reinforced with stiffeners, from the JCAA/JGPP study. Nine PCBs consisting of SnPb, SAC, and SnCu solder were used in this study. Commercially available software simulated modal analysis of the boards to help determine the regions of maximum stress, thus assisting in the placement of accelerometers and stiffeners. Event detectors monitored and recorded intermittence in the solder joints during the vibration test. Results showed a definite reduction in the failure rate from the original study, but it is not certain whether this improvement can be attributed to the stiffeners. Overall, this study did show use of stiffeners is promising. (SMTA International, August 2008)