Bare Board Qualification

“Qualification of Thin Form Factor PWBs for Handset Assembly”
Author: Mumtaz Y. Bora; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Qualification of thin (less than 0.8 mm) PWBs requires careful evaluation of PWB stackup for warpage, delamination and successful Pb-free reflow and rework. This paper presents qualification testing of thin PWBs for warpage characteristics. X-sectional analysis, shear testing, thermal shock, humidity testing and drop test for long-term reliability. (IPC Apex, March-April 2009)

SMT Processing

“Lead-Free Process Development with Thick Multilayer PCBA Density in Server Applications”
Authors: L. G. Pymento, W.T. Davis, Ben Kim and Surangkana Umpo
Abstract: This paper examines the effects of varying surface finishes, temperature-sensitive component limitations, process parameters and resulting interactions that affect solder attach attributes. The study includes characterization of solder joint attributes from a time-zero perspective and extends to accelerated temperature cycling with post-stress characterization. The intent is to document the need to identify design and process options for applications where density and assembly functions extend beyond commercially developed Pb-free solutions. (IPC Apex, March-April 2009)

“SMT Process Characterization and Financial Impact”
Author: Fan Li; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: A number of the companies study the process capability at the time they evaluate or purchase the equipment, or at the time they design the product to fit the process capability. But process capability changes over time. A process or machine that was once capable may not be capable now. The paper focuses on process capability and process control. It suggests process capability study should be routine, rather than a one-time effort. The paper is based on the practices in our company’s manufacturing environment. For placement, the Cpk measurement was trialed on some of our lines. The measurement machine problem was analyzed and a proper measurement machine that fits the requirement was chosen. The Cpk result and product yield after proper calibration were very encouraging. For printing, a DoE was conducted based on a 0.4 mm pitch BGA. The significant factors related to output of paste volume and paste deposit variation were found and an optimum setting combination suggested to production. Process characterization has been proven to have a significant financial impact. (IPC Apex, March-April 2009)

Solderability

“Comparison of Thermal Fatigue Performance of SAC 105 (Sn-1.0Ag-0.5Cu), Sn-3.5Ag, and SAC 305 (Sn-3.0Ag-0.5Cu) BGA Components with SAC 305 Solder Paste”
Authors: Gregory Henshall, Jasbir Bath, Sundar Sethuraman, David Geiger, Ahmer Syed, M.J. Lee, Keith Newman, Livia Hu, Dong Hyun Kim, Weidong Xie, Wade Eagar and Jack Waldvogel; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Many BGA and CSP component suppliers have begun shipment of components with a variety of “second-generation” Pb-free solder ball alloys. Much of the motivation for the alloy changes has been to improve mechanical shock resistance. Several publications have established the improved performance of such second-level BGA/CSP sphere alloys; however, much less has been published regarding the thermal fatigue resistance of components with these new Pb-free ball alloys. As these components and alloys become mainstream, their use in situations where thermal fatigue resistance is critical to product life will become an important consideration. Therefore, understanding thermal fatigue performance for new alloys is necessary. This study compared thermal fatigue performance under accelerated test conditions for three common BGA ball alloys: SAC 105, SnAg3.5, and SAC 305 as a control. Accelerated thermal cycle (ATC) testing was performed using 676 PBGA components with 1.0 mm pitch and electrolytic NiAu finished component pads. These components were assembled to high-temperature rated Cu-OSP-coated printed circuit boards using SAC 305 solder paste, which represents one of the most common assembly practices. ATC testing was performed using IPC-9701A TC1 condition of 0/100°C with 10-min. dwells (nominal); three different failure criteria were used in constructing the Weibull failure curves. The data indicate that SAC 105 has the lowest thermal fatigue resistance among the alloys tested, with SnAg3.5 and SAC 305 having similar and superior performance. Impact of failure criterion on the Weibull curves is also presented. (IPC Apex, March-April 2009)