Fubin Song

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.

Investigation of IMC thickness effect on the lead-free solder ball attachment strength: comparison between ball shear test and cold bump pull test results

Ball pull test has emerged to be an attractive alternative to the traditional ball shear method for characterizing the attachment strength of solder interconnection. Since it is a relatively new development, so far there is not industrial standard to regulate this testing method. This paper discusses the effect of IMC growth after soldering and thermal aging at 150 degC. The attachment strength of solder balls with thermal aging is investigated by ball shear and cold bump pull (CBP) tests. The test configuration and the experimental data are reported in detail. The test results indicate that the CBP test method can reveal the brittle failure of solder joints with a higher sensitivity, especially under the fast pulling speed. As a result, the effect of IMC growth can be identified more easily. In addition to the correlation between the IMC thickness and the solder ball attachment strength, the micro-structure of IMC and the failure modes were discussed as well

Brittle Failure Mechanism of SnAgCu and SnPb Solder Balls during High Speed Ball Shear and Cold Ball Pull Tests

This study investigated brittle solder joint failure mechanisms during high-speed solder ball shear and pull testing. BGA package samples with different solder alloys (Sn4.0%Ag0.5%Cu and Sn37%Pb) were fabricated and a series of solder ball shear and pull tests were conducted at various testing speeds. The ball shear test speeds ranged from 10 mm/s to 3000 mm/s, while the ball pull test speeds ranged from 5 mm/s to 500 mm/s. Following high-speed shear/pull testing, the brittle fracture surfaces of the solder balls and corresponding pad were inspected using SEM/EDX. The results describe an increased incidence of brittle interfacial fracture for SnAgCu solder compared to SnPb solder. Microstructure analysis of brittle solder joint fracture surfaces appears an effective method to aid correlation between board level drop test and high-speed solder ball shear/pull tests.

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.

Corrosion of Sn-Ag-Cu lead-free solders and the corresponding effects on board level solder joint reliability

The drive for lead-free solders in the microelectronics industry presents some new reliability challenges. Sn-Ag-Cu alloys are leading candidates for lead-free solders. Compared to traditional Sn-Pb solders, Sn-Ag-Cu solders are easily corroded in corrosive environment due to their special structure. The presence of Ag3Sn in Sn-Ag-Cu solders accelerates the dissolution of tin from solder matrix into corrosive medium because of galvanic corrosion mechanism. When the corrosion present in the solder joints, it may change the microstructure of corroded regions and decreases the mechanical properties of solder joints by providing a crack initialization. In the present paper, the effects of salt spray test (based on JESD22-A107B) on the microstructure and mechanical properties of Sn-4.0%Ag-0.5%Cu solder balls are investigated with shear and ball pull test. The results show that the shear and pull strength of lead-free solder balls decreased after the slat spray test. In addition, three kinds of tests are performed to evaluate the effects of corrosion on the board level reliability of Sn-Ag-Cu solder joints, including drop test, three-point single strike and cyclic bending

Impact of Ni Concentration on the Intermetallic Compound Formation and Brittle Fracture Strength of Sn-Cu-Ni (SCN) Lead-free Solder Joints

Abstract Cu 6 Sn 5 and Cu 3 Sn are common intermetallic compounds (IMCs) found in Sn–Ag–Cu (SAC) lead-free solder joints with OSP pad finish. People typically attributed the brittle failure to excessive growth of IMCs at the interface between the solder joint and the copper pad. However, the respective role of Cu 6 Sn 5 and Cu 3 Sn played in the interfacial fracture still remains unclear. In the present study, various amounts of Ni were doped in the Sn–Cu based solder. The different effects of Ni concentration on the growth rate of (Cu, Ni) 6 Sn 5 /Cu 6 Sn 5 and Cu 3 Sn were characterized and compared. The results of characterization were used to evaluate different growth rates of (Cu, Ni) 6 Sn 5 and Cu 3 Sn under thermal aging. The thicknesses of (Cu, Ni) 6 Sn 5 /Cu 6 Sn 5 and Cu 3 Sn after different thermal aging periods were measured. High speed ball pull/shear tests were also performed. The correlation between interfacial fracture strength and IMC layer thicknesses was established.

Solder Ball Attachment Assessment of Reballed Plastic Ball Grid Array Packages

The ban of lead in consumer-based electronics by many countries has resulted in a dramatic reduction in the availability of electronic components with tin-lead terminations. With the uncertainty associated with lead-free reliability and the issues associated with mixing lead-free solder with tin-lead solder, medical, defense, and aerospace equipment manufacturers are examining and in some cases implementing reprocessing practices to convert lead-free terminations to tin-lead. For area array packages, the practice is referred to as reballing. While reballing has been used for part reclamation, very little information is available on the reliability of reballed parts. This paper presents lead-free ball grid array (BGA) packages subjected to two ball removal and two ball reattachment techniques. Solder attach strength was used as a metric to examine the reballing process. Both the ball shear test and the cold bump pull (CBP) test were used to test solder strength. The impact of isothermal aging was also examined. The solder strength of reballed BGAs remained at the same level when different reballing methods were used and under different aging conditions. The lead-free non-reballed BGAs had higher solder strength and wider strength distribution than reballed tin-lead BGAs. The pull strength increased as the pull speed increased in the CBP test.

Effects of corner and edgebond epoxy adhesives on board level solder joint reliability of BGA mezzanine connectors

In this paper, the button shear tests of seven kinds of epoxy used for corner/edge bonding of BGA mezzanine connectors are performed firstly for determining adhesive strength between the epoxies and each relevant surface material. The effect of corner/edge bonding epoxy on the board level solder joint reliability of BGA connectors is also investigated including mechanical drop and 4-point bending tests. In addition, the pre-conditioning effect of thermal aging (1000 hours at 125°C) and accelerated temperature cycling (ATC, −40~125°C, 500 cycles) on the reliability of connectors with corner/edge bonding epoxy is discussed. The failure modes and fracture strengths of the button shear and boardlevel tests are cross-referenced for comparison and assessed for correlation. The results from the present study not only contribute to the characterization and selection of corner/edge bonding epoxies for BGA connectors, but also improve the understanding of the corresponding relationship between simple button shear and the more complex and costly boardlevel reliability tests.

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.