Hain Celestial (Canada)

ABSTRACT Innovations in Pb-free solder alloy development are being driven by evolving application requirements. One key area for Pb-free solder alloy development is the need for alloys that can resist thermal fatigue damage in increasingly aggressive product use environments, while providing acceptable performance under drop, shock and vibration loading conditions. Although SnAgCu (SAC) Pb-free solder alloys typically have better fatigue life than traditional eutectic SnPb solder, their fatigue reliability is limited at higher operating temperatures. In response to the need for higher temperature performance, numerous new commercial Pb-free solder alloys are being developed and introduced. These alloys are based on the SAC system but have significant solute additions to promote solid solution strengthening at higher operating temperatures. This paper presents some of the initial thermal cycling results from a major industrial consortia project established to evaluate the thermal fatigue reliability of multiple SAC-based solder alloys containing various combinations of solid solution and dispersion strengthening agents. Daisy chained ball grid array (BGA) test vehicles were fabricated with SAC305 as a baseline and three different developmental alloys each employing significant additions of various combinations of antimony (Sb), indium (In), and bismuth (Bi). The BGA components were soldered to daisy chained test boards using matching alloy solder paste, and subsequently thermally cycled in accordance with the IPC-9701 attachment reliability guideline. Data are reported for three distinct thermal cycling profiles, 0/100°C, -40/125°C, and -55/125°C, as characteristic life  (the number of cycles to achieve 63.2% failure) and slope  from a two-parameter Weibull analysis. A baseline characterization was performed on representative board level assemblies from each of the experimental legs to document the basic microstructures before temperature cycling for comparison to samples removed from the temperature cycling chambers for failure analysis. Microstructural characterization and failure analysis was done using optical metallography (destructive cross-sectional analysis), and scanning electron microscopy (SEM).

ABSTRACT This paper is focused on the microstructure and hardness analysis of new bismuth (Bi) containing alloys that have lower melting and process temperature than the conventional SAC305 solder alloy. One of the main SAC solder drawbacks is fast coarsening of microstructure resulting in degradation of the mechanical and thermomechanical properties during ageing. Seven Bi-containing alloys were used as listed in Table 1. Samples were aged for 25 and 100 hours at 100°C. Alloy hardness was measured after solidification ageing and quenching using a Rockwell hardness tester (HR15T scale with a 1/16” carbide ball indenter). The microstructures after solidification and after ageing were compared using scanning electron microscopy (SEM). The microstructures undergo significant changes upon ageing. Bi particles become uniformly distributed in the Sn matrix. While the hardness of SAC alloys is reduced after annealing, the hardness of these experimental alloys increases. The hardness gradually increases with increasing Bi content, as well as with increasing Ag content. The effect of solid solution strengthening and precipitation hardening mechanisms on microstructure and properties is discussed.

ABSTRACT This paper is in English and Chinese languages. There have been many publications, industry workshops, and symposia that describe process mitigation techniques for minimizing the occurrence of Head-on-Pillow (HoP) defects during surface mount assembly. These include inspection effectiveness as covered in Part 1 of this two paper set. This second paper addresses the root cause of the HoP defect; specifically the link between HoP defects and component warpage. Multiple case studies contributed by the participating companies are presented to support the proposal that the current industry warpage standard needs to be revised and to demonstrate that further work is needed by the industry to understand the root cause of this defect better. Based on the data from the case studies, the authors propose revised acceptance criteria that set the maximum warpage at O.090mm (3.5mil) for BGA of O.8mmpitch and above.

ABSTRACT Selecting an appropriate lead-free alloy for use during wave solder and pin through hole (PTH) rework processes is not a trivial task. Although the electronics industry has been preparing for the conversion from a leaded to a lead-free alloy for almost a decade now, it is apparent that the industry is still within its infancy with respect to selecting a common alloy for these PTH processes. Significant effort has been placed on studying the benefits and drawbacks of a variety of lead-free alloy options available over the past few years. However, with the proliferation of next generation alloys being offered, the task of selecting a common alloy through wave solder and rework processes is being made even more difficult. Industry trends continue to indicate that there is a strengthening movement away from using SAC305 or SAC405 alloys within PTH primary attach/rework soldering operations and a movement towards the use of other alternative lead-free alloys [1]. The main reasons for this shift can be linked to lower procurement costs and lower copper (Cu) dissolution rates. Since many of these alternative lead-free alloys are now starting to gain market share, there is a new issue that has emerged relating to the limited availability of reliability data collected for these new alloy systems. The majority of PTH reliability testing data in existence today relates to SAC305/405 alloys. With the EU RoHS exemption reviews and negotiations continuing, high complexity, high reliability applications including telecom, aviation, storage, and server products may soon fuel demand for alternate lead-free alloys. As a result, it is expected that the need for thermal and mechanical reliability testing of these alternate alloys will increase. This paper, an evolution of earlier work on this topic, discusses results obtained from an internally designed PTH test vehicle constructed to evaluate three commercially available alternative lead-free wave alloys: Sn-Cu-Ni, Sn-Ag-Cu-Bi and Sn-Cu-X by comparing their performance to SAC405 and SnPb alloys. The process performance of each alloy measured during earlier work will be summarized, including profile optimization and process yield analysis. The main intent of this paper is to validate the thermal reliability of a selection of alternative lead-free alloys compared to a SAC405 baseline. The thermal cycling profile used was 0-100°C at 1 cycle per hour (CPH) for 6,000 cycles. Detailed failure analysis is presented to identify and explain observed failure mechanisms. In addition, a comparison of the alloy behavior when subjected to mechanical load conditions vs. non-loaded thermal cycling will be briefly summarized from previous work. The objective of this work is to provide both thermal and mechanical reliability data which can be used to select a suitable wave alloy replacement for SAC305/405. The requirement being that the alternate alloy solution provides similar (or better) overall solder joint quality and reliability, under the conditions tested.

ABSTRACT The thrust of the NEMI project on fiber optic signal performance was to develop fiber optics inspection criteria, which may support differing requirements based on application. The tests’ resulting data would provide OEMs incoming quality and cable suppliers with specific cleanliness requirements with supporting data. Potentially, the inspection criteria could be used as an enhancement to existing TIA, Telcordia and other standards bodies. The influence of the contamination/scratches on connector optical performance, performance being insertion loss (IL) and return loss (RL), as well as on the system level performance using the bit error rate test (BERT), was investigated. It was shown that the effect of contamination/scratches on optical signal performance is dependant on the contamination type (fingerprints, carbon, metallic particles, etc.), the size of the contamination/scratches, and their location on the connector end face. The influence of the contamination/scratches becomes more evident if they are located in the core/cladding areas. It was shown that particle contamination may cause a significant increase in IL (up to ten times), decrease in RL (up to 3 times), and increase in BERT results (2-10 times). The significant degradation in BER performance occurred when the core of the fiber was blocked. The BER signal increased by more than 100 times compared with a clean fiber at average power -12 dBm. Scratches applied to the fiber MFD (mode field diameter) resulted in an increase of up to 25% of RL, while scratches located in the cladding layer showed little effect on IL, RL, and the BERT results. Multiple heavy scratches passing through the core caused severe performance degradation (IL, RL) and catastrophic BERT failures. Further investigations, such as mathematical modeling, are required to understand the influence of contamination/scratches on optical signal performance. The other objective of the project was to determine methods for improving the cleaning process and preventing recontamination of fiber optic connectors. This would result in the minimization of inspection and cleaning processes, elimination of false failures during test due to contaminated connectors, reduced cycle times, and associated cost reductions.

ABSTRACT IBM Numa-Q designed and assembled twelve test vehicle boards, each containing 1400 0201 resistor packages. The boards were assembled in a production environment at the Celestica Toronto facility in April of 2000. The research summarized in this paper will address issues surrounding the design of printed circuit boards and assembly of 0201 components. Board construction, pad patterns, via in pad, component spacings, and component selection will be discussed. From an assembly view point, 0201 components result in unique challenges. This paper will address challenges in assembly including: stencil design, paste screening, pick-n-place equipment, reflow profiling, and a summary of defects.