Keith Newman

BGA brittle fracture - alternative solder joint integrity test methods

A solder ball shear and pull testing study was conducted on 27 unique package constructions, evaluated under a wide variety of test conditions. The study encompassed the coordinated efforts of 7 electronics manufacturers using early-prototype high speed solder ball shear/pull equipment. Shear speeds ranged from a conventional 0.0001 m/s (100 /spl mu/m/s) rate up to as high as 4 m/s, while pull testing ranged from speeds of 0.0005 m/s (500 /spl mu/m/s) to 1.3 m/s. The many package configurations varied in substrate plating type (exposed Cu, electrolytic NiAu and electroless-Ni/immersion-Au), solder composition (SnPb, SnPbAg and SnAgCu), packaging construction and materials, solder and package geometries, package assembly location, and time between reflow and test.

High-Speed Solder Ball Shear and Pull Tests vs. Board Level Mechanical Drop Tests: Correlation of Failure Mode and Loading Speed

This study compares high-speed bondtesting (shear and pull) with board level drop testing (BLDT) of BGA packages using Sn4.0%Ag0.5%Cu solder balls and either an ENIG or OSP package substrate surface finish. High-speed shear and pull testing were carried out at various speeds; failure modes were recorded, together with force and fracture energy data. In addition, detailed microscopic analysis (SEM and EDX) was executed on both complementary surfaces (ball and pad) of brittle fracture failures from both shear and pull test samples. The results of these studies showed close similarity to those from brittle fractures generated during BLDT of the same packages. Furthermore, there was strong correlation between various bondtesting parameters at which brittle fractures occurred and the number of drops to failure seen in BLDT. In summary, it is suggested that brittle fractures obtained in high-speed bondtesting are a strong indicator of BLDT behavior.

Effect of Thermal Aging on High Speed Ball Shear and Pull Tests of SnAgCu Lead-free Solder Balls

Solder joint reliability concerns are increasing exponentially with the continuous push for device miniaturization, and the expanded use in portable electronic products. In order to predict the solder joint reliability under drop conditions, it is important to increase the testing speed of package level test methods, such as high-speed solder ball shear and pull. Traditional ball shear and pull tests are not considered suitable for evaluation of joint reliability under drop loading, since the applied test speeds, usually lower than 5 mm/s, are well below the impact velocity applied to the solder joint in a drop test. Recently, high-speed shear and pull test equipment (Dage 4000HS) with testing speeds beyond 1,000 mm/s has become available. The present study continues the efforts reported recently and investigates the effect of thermal aging on the attachment strength and fracture energy of SnAgCu lead-free solder balls during high speed ball shear/pull tests. The ball shear test speeds ranged from 100 mm/s to 1,000 mm/s, while the ball pull test speeds ranged from 5 mm/s to 100 mm/s. The test specimens were aged at 125degC or 150degC for durations of 100, 300 and 500 hrs, with some additional samples exposed up to 1,000 hrs. Correlations were established between solder joint fracture force/energy and IMC thickness, and between fracture energy and failure mode.

Comparison of Joint Strength and Fracture Energy of Lead-free Solder Balls in High Speed Ball Shear/Pull Tests and their Correlation with Board Level Drop Test

A comprehensive solder joint reliability study was conducted using both high-speed solder ball shear/pull and board level drop testing (BLDT). The samples were divided into groups which were subject to various periods of thermal aging (125degC, up to 500 hours) in order to accelerate the formation of intermetallic compound (IMC) in the solder joints. The ball shear tests ranged from 10 mm/s to 3,000 mm/s while the ball pull tests ranged from 5 mm/s to 500 mm/s. A total of 6 unique package constructions were evaluated, ranging from a 316 PBGA (27 mm, sq) to a 2,395 CBGA (51 mm, sq). The samples used SAC lead-free solder balls and a variety of pad surface finishes. Detailed failure analyses were performed to identify the failed solder joints and corresponding failure modes. The failure modes and loading speeds of ball shear and ball pull tests were cross-referenced with the mechanical drop tests for comparison. Correlation models were established relating drops-to-failure with both solder ball fracture force and energy.

Material characterization of corner and edgebond epoxy adhesives for the improvement of board-level solder joint reliability

In this paper, the material characteristics of six epoxies used for corner/edge-bonding are analyzed and compared to board-level mechanical reliability test. An innovative material characterization approach, button shear testing, provided an expedient method of determining adhesive strength between the epoxies and each relevant surface material. The board-level test included mechanical shock test. A number of SMT test devices are evaluated, including 1849 CBGA packages, and 190 ball count mezzanine connectors. The failure modes and fracture strengths of the material characterization tests and board-level tests are cross-referenced for comparison, and assessed for correlation. The results from the present study not only contribute to the characterization and selection methods of corner/edge-bonding epoxies, but also improve understanding of the corresponding relationship between material characterization testing and the more complex and costly board-level reliability tests.

Investigation of lead-free BGA solder joint reliability under 4-point bending using PWB strain-rate analysis

Board level solder joint reliability was evaluated using a 4-point monotonic bending test on different BGA package assemblies, including a 51×51 mm 2400 CBGA and a 40×40 mm 1517 PBGA. The edgebond epoxy was applied between the package samples and solder-attached printed wiring boards (PWBs). During the bending test, the PWB strain, bending force and daisy-chain resistance were monitored in real time. The daisy-chain resistance and PWB strain-rate during the bending test were cross-referenced for detailed comparison. The test results indicated that the PWB strain-rate showed an obvious change at the moment of package failure. The PWB strain-rate can be a useful monitoring method for detecting the onset of the solder joint failure during the monotonic bending test.

Investigation of mixed SAC and SnPb solder balls under high speed ball shear and pull tests

Due to environmental consciousness and legislative regulations, Pb-free solders have been increasingly used for replacement of conventional SnPb solders in the microelectronic industry. However, during the transition period from SnPb to Pb-free solders, some products will potentially consist of mixtures of Pb-free with SnPb solders. This paper presents the results of microstructural analysis of mixed solder joints which are formed by attaching different alloys of solder balls and pastes on the OSP pad finish. The effect of thermal aging on the strength and fracture energy of the mixed solder balls during high speed ball shear/pull tests was also investigated in the study. The test specimens were aged at 125°C for durations of 200, 500 and 1000 hours. The correlations between the solder ball fracture force/energy, failure modes and intermetallic compound (IMC) thickness of the mixed alloy solder joints are also established.

Surface analysis of outgassing contamination from edgebond epoxy adhesives on ImAg pads

This paper details the outgassing process during epoxy degradation and evaluates the corresponding influence on adjacent PWB pads for immersion Ag (ImAg) plated circuit boards. Three commercial epoxy adhesives used for edge-bonding of surface-mount (SMT) components were investigated. Scanning electron microscope (SEM) analysis and electron dispersive spectroscopy (EDS) was carried out to investigate the surface of the contaminated ImAg pads. Chemical states of the elements transferred to the pads were analyzed by X-ray Photoelectron Spectroscopy (XPS). The results from the present study showed some ingredients in the adhesives may be thermo-oxidized to gaseous by-products in the presence of oxygen and migrate out from the epoxy body, contaminating the adjacent ImAg pads. Further research will be needed to verify whether these gaseous by-products also contaminate surrounding components, and result in corrosion-related reliability failures.