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Saturday, 28 February 2009 19:00
Technical Abstracts

Component Processing

“Implementation of 01005s: A Case Study”

Authors: Paul N. Houston, Gary L. Turpin and Daniel F. Baldwin, Ph.D.; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: This paper presents a production part implementation case study for 01005 passive components, including a review of some process challenges that were encountered, 01005 rework, and highlights in design for manufacturability. From the process perspective, implementation challenges for 01005s were mainly the print and placement process. The main challenge of the print process was getting a consistent amount of solder paste through the extremely small apertures used for the 01005s. Some issues with the placement process included pickup reliability, visioning and placement accuracy. The reflow process previously established for 0201 components yielded very similar results during the implementation of 01005s. Rework of 01005 passives presented another unique opportunity for process improvements. From a DfM perspective, pad design and pad-to-pad spacing had a significant influence on first-pass yields. (SMTA Pan Pac Microelectronics Symposium, February 2009)

Repair

“Impact of PCB Pad Site Dress Methods on Pad Array Damage”

Authors: Laurence A. Harvilchuck, Brian Roggeman, Raiyo F. Aspandiar, James M. Wade and Gaurav Godbole; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: The thermal profile experienced by the pad array can have a profound impact on latent PCB damage, including the presence or absence of pad cratering. In this exercise, pad array damage is evaluated as a function of assembly preheating, pad site dress method, and applied desoldering temperature to offer insight when choosing between simple wick-and-iron solder removal and the more sophisticated vacuum–assisted solder scavenging methods. High-resolution 16-channel thermal profiles were obtained of both the wick-and-iron and vacuum scavenging operations across a single 34 mm square pad array of variable pitch on a 0.060" thick Pb-free ATX motherboard, revealing the nature of the thermal profile at the pad surface and through the board section to the cores. The shortcomings of current repair thermometry methods are also documented in the context of the impact of thermocouple placement on profile accuracy. Process variations inherent in the primarily manual wick-and-iron solder removal methods are readily apparent in the thermal profiles experienced by the pad array, while significantly reduced in the thermal profile generated by the vacuum scavenger. Wick-and-iron scavenging operations can subject the pad array to ramp rates approaching 200°C/sec. during the brief excursion above solder liquidus, while vacuum scavenging of the same site exhibited a maximum ramp rate nearly a full order of magnitude less, but of much greater times above liquidus. The impact of the thermal profile on the pad array was characterized by bump pull, pad fatigue and dye-and-pry techniques. Results from the present study showed no solder mask damage in the vicinity of the pad array resulted from any of the scavenging processes. Damage to innerlayer circuit board structures (per IPC-A-610) beneath the pad array was also absent in all cases under study. Use of substrate preheating during solder scavenging has a definite impact on reducing the substrate damage that can result from the repair of lead-free laminates. For both the wick-and-iron and vacuum methods, higher applied desoldering temperatures resulted in weaker pad adhesion than the corresponding solder removal operations at lower applied desoldering temperatures. Further pad fatigue testing of the same samples indicated this change in pad adhesion strength may be related to a change in the ductility of the laminate directly beneath the pad. The laminate choice also can have a significant impact. (SMTA Pan Pac Microelectronics Symposium, February 2009)

Testing

“Quality and Reliability Testing of Circuit Boards Assembled with Lead-Free Components, Finishes, Soldering Materials and Processes in Simulated Production Conditions”

Authors: Sammy Shina, Ph.D., et al; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: In the New England Lead-Free Electronics Consortium’s fourth phase of testing, which began in 2007, several simulated conditions of assembly and rework processes were evaluated in a matrix of multiple levels of components, PWB Pb-free surface finishes and solders, and compared to a baseline of leaded equivalent materials and processes. PTH and SMT technologies were evaluated. The assembly portion of the testing and rework is complete, and long-term reliability and vibration testing is ongoing. All quality and reliability testing was performed with industry standard methodologies, using specially trained production inspectors for the quality evaluation, and extreme thermal cycling for reliability testing. Results indicate that with proper selection of currently available (2008) materials and finishes and careful control of assembly processes, successful Pb-free assembly and rework can be achieved. Reliability testing to date showed interesting inflection points for leaded versus Pb-free reliability that has to be resolved by additional thermal cycling. (SMTA Pan Pac Microelectronics Symposium, February 2009)

 

Columns

Eastern-US: China’s New Competitor?

Parity emerges among EMS Factories from Asia, Mexico and the US.

For the first time in years we see parity in the Eastern US among EMS factories from Asia, Mexico and the US. This EMS market condition will permit American OEMs (the EMS industry refers to OEMs as customers) to have more EMS pathways to choose from. Now more than ever, such EMS assignments will require deeper investigation relating to the OEMs’ evaluation of manufacturing strategies.

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The Human Touch

For those who count on the electronics industry for big feats, it’s been a remarkable couple of years.

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Features

Advances in Concentration Monitoring and Closed-Loop Control

Contaminated bath water skews refractive index results. New technology can accurately measure aqueous cleaning agent concentration.

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Circuits Disassembly: Materials Characterization and Failure Analysis

A systematic approach to nonconventional methods of encapsulant removal.

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