Technical Articles From Agilent Technologies, Inc.

Good Product Quality Comes From Good Design for Test Strategies

Dec 17, 2015 | Adrian Cheong

Product quality can be improved through proper application of design for test (DFT) strategies. With today's shrinking product sizes and increasing functionality, it is difficult to get good test coverage of loaded printed circuit boards due to the loss of test access. Advances in test techniques, such as boundary scan, help to recover this loss of test coverage. However, many of these test techniques need to be designed into the product to be effective.

This paper will discuss how to maximize the benefits of boundary scan test, including specific examples of how designers should select the right component, connect multiple boundary scan components in chains, add test access to the boundary scan TAP ports, etc. A discussion of DFT guidelines for PCB layout designers is also included. Finally, this paper will include a description of some advanced test methods used in in-circuit tests, such as vectorless test and special probing methods, which are implemented to improve test coverage on printed circuit boards with limited test access....

Pad Cratering Susceptibility Testing with Acoustic Emission

Aug 13, 2015 | Wong Boon San, Julie Silk; Agilent Technologies | Richard Nordstrom, Ph.D.; Acoustic Technology Group,

Pad cratering has become more prevalent with the switch to lead free solders and lead free compatible laminates. This mainly is due to the use of higher reflow temperature, stiffer Pb-free solder alloys, and the more brittle Pb-free compatible laminates. However, pad cratering is difficult to detect by monitoring electric resistance since pad cratering initiates before an electrical failure occurs.

Several methods have been developed to evaluate laminate materials' resistance to pad cratering. Pad-solder level tests include ball shear, ball pull and pin pull. The detailed methods for ball shear, ball pull, and pin pull testing are documented in an industry standard IPC-9708. Bansal, et al. proposed to use acoustic emission (AE) sensors to detect pad cratering during four-point bend test. Currently there is an industry-working group working on test guidelines for acoustic emission measurement during mechanical testing....

Effect of Gold Content on the Microstructural Evolution of SAC305 Solder Joints Under Isothermal Aging

Aug 29, 2013 | Mike Powers, Jianbiao Pan, Julie Silk, Patrick Hyland

Au over Ni on Cu is a widely used printed circuit board (PCB) surface finish, under bump metallization (UBM), and component lead metallization. It is generally accepted that less than 3 wt.% Au in Sn-Pb solder joints inhibits formation of detrimental intermetallic compounds (IMC). However, the critical limit for Au content in Pb-free solder joints is not well established. Three surface-mount package platforms, one with a matte Sn surface finish and the others with Ni/Au finish, were soldered to Ni/Au-finished PCB using Sn-3.0Ag 0.5Cu (SAC305) solder, in a realistic manufacturing setting. The assembled boards were divided into three groups: one without any thermal treatment, one subjected to isothermal aging at 125°C for 30 days, and the third group aged at 125°C for 56 days... ...

Boundary Scan Advanced Diagnostic Methods

Feb 14, 2013 | Christopher Cain

Boundary-scan (1149.1) technology was originally developed to provide a far easier method to perform digital DC testing to detect intra-IC interconnect assembly faults, such as solder shorts and opens. Today's advanced IC technology now includes high-speed differential interfaces that include AC or DC coupling components loaded on the printed circuit assembly. Simple stuck-at-high/low test methods are not sufficient to detect all assembly fault conditions, which includes shorts, opens and missing components. Improved diagnostics requires detailed circuit analysis, predictive assembly fault simulation and more complex testing to isolate and accurately detect all possible assembly faults... First published in the 2012 IPC APEX EXPO technical conference proceedings...

The Morphology Evolution and Voiding of Solder Joints on QFN Central Pads with a Ni/Au Finish

Oct 18, 2012 | Julie Silk, Jianbiao Pan, Mike Powers

First published in the 2012 IPC APEX EXPO technical conference proceedings. In this paper, we report on a comprehensive study regarding the morphology evolution and voiding of SnAgCu solder joints on the central pad of two different packages – QFN and an Agilent package called TOPS – on PCBs with a Ni/Au surface finish....

Evaluation of Laminates in Pb-free HASL Process and Pb-free Assembly Environment

Sep 20, 2012 | Khaw Mei Ming, Andrey Lee

First published in the 2012 IPC APEX EXPO technical conference proceedings. An evaluation of four FR4 laminates in commonly used stack-ups was done to determine their survivability for the Pb-free HASL process followed by a worst case Pb-free manufacturin...

Thermal Cycle Reliability Study of Vapor Phase BGA Solder Joints

Sep 13, 2012 | Ward Gatza; Agilent Technologies, Inc., Tom Evans; Thomas C. Evans Consulting

First published in the 2012 IPC APEX EXPO technical conference proceedings. Prior to committing production boards to vapor phase soldering, we performed an evaluation to assess reliability and evaluate the vacuum soldering option. The reliability of vapor...