Shear Strength Of Solder Bumps Research Articles

Influence of thermal shock cycles on Sn-37Pb solder bumps

PurposeWith continuous concerning on the toxic of element Pb, Pb-free solder was gradually used to replace traditional Sn-Pb solder. However, during the transition period from Sn-Pb to Pb-free solder, mixing of Sn-Pb and Pb-free is inevitable occurred in certain products, and in China where Sn-Pb solder was still used extensively in certain areas especially. Correspondingly, understanding reliability of Sn-Pb solder joints was very important, and further studies were needed.Design/methodology/approachThermal shock test between −55°C and 125 °C was conducted on Sn-37Pb solder bumps in the BGA package to investigate the microstructure evolution and the growth mechanism of interfacial intermetallic compound (IMC) layer. The effects of thermal shock on the mechanical property and fracture behavior of Sn-37Pb solder bumps were discussed.FindingsPb-rich phase was coarsened and voids were increased at first; Pb-rich phase was refined and voids were decreased secondly with the increase of thermal shock cycles; the shear strength of solder bumps was slightly decreased after thermal shock, but was back up to 73.67MPa at 2,000 cycles; interfacial IMCs of solder bumps was from typical scallop-type into smooth, the composition of IMCs was from Cu6Sn5 into Cu6Sn5 and Cu3Sn after thermal shock with 1,500 and 2,000 cycles; 20.0 per cent of solder bumps at 1,500 cycles and 9.5 per cent of solder bumps at 2,000 cycles were failure respectively.Originality/valueCompared with the board level test method, the impact shear test for the single solder bump is more convenient and economical and is actively pursued by the industries. The shear strength of solder bumps was slightly decreased after thermal shock, but was back up to 73.67 MPa at 2,000 cycles; 20.0 per cent of solder bumps at 1,500 cycles and 9.5 per cent of solder bumps at 2,000 cycles were failure.

Study of Thermal Aging Effects on Intermetallic Growth Mechanisms and Shear Strength Behavior of Wafer-Level Solder Bumps

The effect of wafer-level solder bump size on solder bump shear strength and intermetallic growth as a function of time, at different storage temperatures is studied, using solder bumps of two different heights: 95 mum (SB95) and 142 mum (SB142). Smaller solder bumps (SB95) lead to a faster decrease in bump shear strength. Increasing aging temperature and time brings about an increase in the final fracture area of the solder, from a ductile to a quasi-brittle failure mode. It is observed that the smaller solder bump (SB95) exhibits a faster rate of increase in final fracture area, than the bigger bump. A linear decrease of solder bump shear strength with intermetallic thickness is established for the systems studied. Degradation of solder bump shear strength is found to be affected by the relative volume of the solder bump with respect to Ni/Au, such that a lower solder bump to Ni/Au volume ratio leads to faster shear strength degradation, due to the consumption of Cu in the bulk solder bump and the formation of brittle intermetallics. The overall intermetallic growth activation energies for the two solder bump sizes are found to be comparable, at 0.85- 0.86 eV. For this study, (Cu,Ni) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> , is initially formed, at the solder bump-to-under bump metallization (UBM) interface, followed by the formation of (Ni,Cu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , between the UBM and the (Cu,Ni) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> intermetallic layer.

Sub-100 μm SnAg Solder Bumping Technology and the Bump Reliability

Lead-free solder bumping and its related interconnection and reliability are becoming one of the important issues in today’s electronic packaging industry. In this paper, alloy electroplating was used as SnAg solder bumping process. Multiple reflow was preformed on as-plated solder bumps. Scanning electron microscopy and energy dispersive X-ray analysis were used to investigate the intermetallic compound and microvoids of cross-sectioned solder bump. Shear test was used to evaluate the reliabilities of the SnAg bumps. The 13×13 area-array Sn/3.0Ag solder bumps of 70 μm in height and 90 μm in diameter were fabricated with a smooth and shiny surface and with a uniform distribution of Ag. During multireflow, the scalloped Cu6Sn5 phase grows by a ripening process. Volume shrinkage was the main reason for the formation of microvoids during multireflow. The average shear strength of solder bumps on TiW/Cu under bump metallurgy (UBM) increased with reflow times. The electroplating process is suitable for mass production of well-controlled geometry and uniformity of SnAg solder bumps. Microvoids have trivial negative impacts on the solder bonds. The combination of TiW/Cu UBM and SnAg solder is reliable.

Preparation and Temperature Cycling Reliability of Electroless Ni(P) Under Bump Metallization

The reliability of electroless Ni(P) under-bump metallization (UBM) was evaluated via temperature cycling and solder bump shear strength tests. Commercial diodes and dummy dies fabricated in-house were used as substrates for the electroless Ni(P) UBM deposition. Solder bumps were formed after reflowing eutectic 63Sn37Pb solder foils over the Ni(P) UBM. The solder bump shear strength was measured before and after different temperature cycling. The results from this study showed that the UBM thickness and dimension had important effects on the solder bump shear strength and reliability. Both the larger UBM dimension and larger UBM thickness tended to induce higher stress in the UBM, which resulted in the lower solder bump shear strength and lower temperature cycling reliability. A better UBM structure solution for high current electronic packaging application is indicated in this paper

Microstructure and shear strength evolution of Sn-Ag-Cu solder bumps during aging at different temperatures

Flip-chip devices with Sn-3.8Ag-0.7Cu solder on electroless Ni (EN) without immersion Au were studied after aging at different temperatures. The (Cu,Ni)6Sn5 intermetallics (IMCs) growth was volume diffusion controlled and Kirkendall voids were found in the Ni3P layer even at the initial stage of high-temperature aging due to the faster diffusion of Ni in the Ni3P layer via its column structure boundaries. The Ag3Sn IMCs were distributed in the bulk solder, existing as plate- or lamella-like phases or as small particles around the β-Sn dendrites, and the (Cu,Ni)6Sn5 IMCs existed as facet-like phases. The plate- and lamella-like Ag3Sn phases break up into small parts and these broken parts, together with small Ag3Sn particles, coarsen into pebble-like phases during high-temperature aging. Shear tests showed that all the solder bumps fractured in the bulk solder. The shear strength of solder bumps decreases at the initial stage of aging at 150°C and 175°C, and the strength degradation during aging may be caused by the coarsening of small Ag3Sn particles.

Isothermal aging effects on the microstructure and solder bump shear strength of eutectic Sn37Pb and Sn3.5Ag solders

The reliability of the eutectic Sn37Pb (63%Sn37%Pb) and Sn3.5Ag (96.5%Sn3.5%Ag) solder bumps with an under bump metallization (UBM) consisting of an electroless Ni(P) plus a thin layer of Au was evaluated following isothermal aging at 150 °C. All the solder bumps remained intact after 1500 h aging at 150 °C. Solder bump microstructure evolution and interface structure change during isothermal aging were observed and correlated with the solder bump shear strength and failure modes. Cohesive solder failure was the only failure mode for the eutectic Sn37Pb solder bump, while partial cohesive solder failure and partial Ni(P) UBM/Al metallization interfacial delamination was the main failure mode for eutectic Sn3.5Ag solder bump.

Al surface morphology effect on flip-chip solder bump shear strength

This paper reports the result of a study on the effect of aluminum pad surface morphology on the flip-chip solder bump reliability. The influence of the Al surface morphology on the electroless zinc/nickel/gold UBM is presented. The reliability of the solder bump as measured by ball shear force is reported. Al pad were produced using two RF sputtering systems: CVC-601 and Varian-3180. The Al targets used in CVC and Varian system were 99%Al–1%Si and 98.95%Al–1%Si–0.05%Ti respectively. The surface of the CVC sputtered Al samples were smooth while the surface of the Varian sputtered Al samples were rough. All the samples were subjected to the electroless zinc/nickel/gold plating. The results suggest that after plating, the smooth Al surface resulted in a fine nickel UBM surface while the rough Al surface formed a coarse nickel UBM surface. Ball shear test was conducted after the solder balls were bumped on the UBM. Result shows that the fine UBM surface samples have twice the shear strength compared to the samples with coarse UBM surface samples. The analysis of the results indicates that shear surface occurred at the UBM and the solder interface for samples with rough UBM surface leading to the lower shear strength. Nickel bump shear test result shows that pretreatment of Al pad surface by sodium hydroxide and nitric acid created more zinc seeds this led to better electroless nickel plating. Nickel bump shear tests also shows that double zincated bumps had higher shear strength than single zincated bumps. To obtain reliable flip-chip solder bumps, it is essential to maintain good Al pad surface morphology, pretreatment of the Al pad and undergo second zincation.

Effect of Cu stud microstructure and electroplating process on intermetallic compounds growth and reliability of flip-chip solder bump

In electroplating-based flip-chip technology, the Cu stud and solder deposition processes are two of the most important factors affecting the reliability of solder joints. The growth of Cu-Sn intermetallic compounds (IMC) also plays a critical role. In this paper, the effect of Cu stud surface roughness and microstructures on the reliability of solder joint was studied. The surface roughness of the Cu stud was increased as the Cu electroplating current density increased. The microstructural morphology of the Cu-Sn IMC layer was affected by Cu stud surface structure. We found the growth rate of IMC layer increased with the increasing of Cu stud grain size and surface roughness during aging test. The growth kinetics of Cu-Sn intermetallic compound formation for 63Sn/37Pb solder followed the Arrhenius equation with activation energy varied from 0.78 eV to 1.14 eV. The ratios of Cu/sub 3/Sn layer thickness to the total Cu-Sn IMC layer thickness was in the range of 0.5 to 0.15 for various Cu microstructures at 150/spl deg/C during thermal aging test. The shear strength of solder bump was measured after thermal aging and temperature/humidity tests. The relationship between electroplating process and reliability of solder joints was established. The failure mode of solder joints was also analyzed.

Mechanical Properties and Fracture Behavior of the Cu and Cu6Sn5–Dispersed Sn-Pb Solder Bumps Processed by Screen Printing

ABSTRACTThe mechanical properties of the 1-9 vol % Cu and Cu6Sn5-dispersed 63Sn-37Pb solder alloys were characterized with tensile test. Also, the Cu and Cu6Sn5-dispersed 63Sn-37Pb solder bumps of 760 μm size were fabricated on the Au(5 μm)/Ni(5 μm)/Cu(27 μm) BGA substrates by screen printing process, and their shear strength were characterized with variations of the dwell time at the reflow peak temperature(220°C) and aging time at 150°C. The yield strength and ultimate tensile strength of the 63Sn-37Pb solder alloy increased with dispersion of 1-9 vol % Cu and Cu6Sn5. In general, however, the Cu and Cu6Sn5-dispersed solder bumps exhibited lower shear strengths than those of the 63Sn-37Pb solder bumps The failure surface of the solder bumps after ball shear test could be divided into two regions of slow crack propagation and critical crack propagation, and the shear strength of solder bumps was inversely proportional to the slow crack propagation length.