Cristina Andersson

Effect of different temperature cycle profiles on the crack propagation and microstructural evolution of lead free solder joints of different electronic components

Temperature cycling of real electronic components was carried out in a systematic manner at two different temperature profiles in a single-chamber Heraeus climate cabinet. The first temperature profile ranged between -55/spl deg/C and 100/spl deg/C and the second between 0/spl deg/C and 100/spl deg/C. Top-side SMD components were soldered with Sn-3.8Ag-0.7Cu lead free solder paste and hole mounted components and bottom side SMD components were wave soldered with Sn-3.5Ag alloy. Both through-hole (dual in line (DIL) packages) and surface mounted components (chip resistors and ball grid arrays (BGA)) were investigated in this work. Crack initiation and propagation was analyzed after every 500 cycles while microstructural evolution as a function of the number of temperature cycles was analyzed after every 500 cycles for each temperature cycling profile. In total, 3000 cycles were run at both temperature profiles. The observation results from each profile were compared. Finite element modeling (FEM) calculations were performed, where strain and stress analysis of chip resistor joint performance corroborates the experimental work results, especially regarding the crack initiation sites. For temperature cycling ranging between -55/spl deg/C and 100/spl deg/C, cracks were visible already after 500 cycles for the DIP-packages. For the other temperature profile and DIP-packages, cracks initiated sometime between 1000 and 1500 cycles. The cracks observed after 1500 cycles were visibly smaller for the temperature profile ranging between 0/spl deg/C and 100/spl deg/C, concluding that crack initiation and propagation was slightly slower for this temperature profile. After 2000 cycles, cracks were also observed in chip resistor solder joints mounted on the secondary side of the test boards. Cracks continued to propagate as a function of temperature cycles. With regard to microstructural observation, differences could also be observed between the two temperature profiles. Microstructural changes happened faster in the first temperature profile than in the second one.

Thermal Cycling Aging Effect on the Shear Strength, Microstructure, Intermetallic Compounds (IMC) and Crack Initiation and Propagation of Reflow Soldered Sn-3.8Ag-0.7Cu and Wave Soldered Sn-3.5Ag Ceramic Chip Components

Temperature cycling of electronic components was carried out at two different temperature profiles, the first ranging between -55degC and 100degC (TC1) and the second between 0degC and 100degC (TC2). Totally, 7000 cycles were run at TC1 and 14500cycles at TC2. The test boards top-side components were surface mounted using Sn-3.8Ag-0.7Cu solder alloy, and the bottom side surface mount devices (SMD) were wave soldered with Sn-3.5Ag alloy. The solder joint degradation was investigated as a function of cycle number by means of shear force measurements and cross-sectioning. The shear force drop was correlated to both crack initiation time and propagation rate, and microstructural changes. The effect of manufacturing process (reflow versus wave soldering) and component size (0805 versus 0603 components) on the shear force were also investigated. For both reflow and wave soldered components, the harsher the test environment the faster and largest the decrease in shear force. The shear force is higher for the 0805 components compared to the 0603. The effect of component size on the residual shear force is higher for the testing condition TC1. TC1 also seems to have a higher effect on the residual shear force compared to TC2. The main difference between wave soldered and reflow soldered components is that the shear force is in average higher for the wave soldered components compared to the reflow soldered. For the reflow soldered components using SAC, the microstructure coarsens as a function of temperature cycling, especially the Ag3Sn intermetallic particles. Furthermore, this alloy shows an increase in intermetallic compound (IMC) layer thickness (Cu-Ni-Sn), and its growth is controlled by a diffusion mechanism. The IMC growth coefficient is for the SAC system tested at TC1 0.0231 mum/h1/2 (0.00053 mum/h) and for TC2 0.0054 mum/h1/2 (2.9*10-5 mum/h). The microstructural changes during thermal cycling are a result of both static and strain-enhanced aging. For the wave soldered components the microstructure also became coarser, however, the IMC layer (Ni3Sn4) thickness did not change. The IMC layer growth does not affect the shear force for the test conditions applied in this work. The shear force decrease observed in the present work as a result of thermal cycling is a result of both microstructural coarsening and crack propagation inside the solder joint.

Recent Development of Nano-solder Paste for Electronics Interconnect Applications

Conventional lead-free solders, with a solder alloy particle size in the micrometer range, present some major disadvantages, such as relatively high melting temperatures, which can result in defects and build up stresses during reflow processing, and limited application for high density, ultra- small pitch electronic applications. By decreasing the size of the solder alloy particles to the nanometer range, one can both decrease the melting temperature of the solder alloy and use such solders in very fine pitch applications. Besides lower melting temperature, particles in the nanometer size range present many other extraordinary properties, such as, large surface area per unit volume, large surface energy, supermagnetism, extraordinary optical properties, self- purification properties and quantum size effects. It is all these extraordinary properties that have attracted the attention of both scientific and technological communities all over the world. The main focus of this paper is the recent development of both composite solders and pure nano-solder pastes and their application as electronic interconnect materials. The paper starts by giving and introduction to the subject of nanoparticles, including definitions, advantages and general applications. This is followed by a section dealing with the main manufacturing processes presently being used to manufacture solder alloy nanoparticles. The two main sections of this article deal with composite solders and pure nanosolder pastes. The first part, regarding composite solders, deals with the issues related to adding nanoreinforcements into conventional micrometer-sized solders and the effect of such reinforcements on both the mechanical and physical properties of solder alloys. The second part deals with pure nano-solder pastes and their application in electronic interconnect applications.

A compact V-band planar wideband bandpass filter based on Liquid Crystal Polymer substrates

The move to higher frequencies has stimulated the development of the materials and integration techniques of the RF/microwave/millimeter (mm)-wave areas. Until now, materials commonly used at high frequency are either expensive or have inadequate performance. Liquid crystal polymers (LCPs), have attracted much more attention as advanced candidates as RF/microwave/mm-wave substrate materials for commercial wireless applications due to their combination of features and performance. In this paper, a compact V-band planar microstrip bandpass filter with sharp-rejection, low insertion-loss and wide-bandwidth based on the dual-mode ring resonator is proposed. The filter is fabricated on a LCP substrate by using standard processing technology. The proposed filter exhibits a return loss level better than 10 dB, an insertion loss of 5 dB, and a 3-dB bandwidth of 30%. The simulated and measured results are compared and agree well, which shows the promising potential of LCP laminates for flexible RF/microwave/mm-wave substrates.

Characterization of Nanoparticles of Lead Free Solder Alloys

Nanoparticles of Sn-4.0Ag-0.5Cu and Sn-0.4Co-0.7Cu (wt% composition) lead free solder alloys were manufactured and characterized for potential applications in microelectronics packaging. Scanning electron microscopy (SEM) analysis was carried out in order to study the morphology and size distribution of the nanoparticles. It was observed that nanoparticles of lead free alloys were almost spherical in shape. The observed size distribution of both lead free solder alloy nanoparticles is between 20 ~ 80 nm. High resolution transmission electron microscopy (HRTEM) was used to analyse the detailed nanostructure and oxide layer present on the nanoparticles surface. The observed oxide layer thickness is about 25Aring (2.5 nm). The depression in melting point due to nanosize effect was calculated theoretically as a function of particle size for the above mentioned lead free solder alloys and the theoretical results were compared with differential scanning calorimeter (DSC). Onset calculation was used to determine the depression in melting point due to nanosize effect in respect to bulk material. The melting point difference obtained by DSC for Sn-4.0Ag-0.5Cu and Sn-0.4Co-0.7Cu lead free solders are between 1.1 to 7.8degC and 0.24 to 2.4degC respectively depending on the definition of the melting point determination by DSC

Coffin‐Manson constant determination for a Sn‐8Zn‐3Bi lead‐free solder joint

Purpose – To determine the Coffin‐Manson (CM) equation constants for fatigue life estimation of Sn‐8Zn‐3Bi solder joints, since Sn‐8Zn‐3Bi solder has a melting temperature of around 199°C which is close to that of the conventional Sn‐Pb solder which has previously been used in the electronics assembly industry.Design/methodology/approach – Three dimensional finite element (FE) simulation analysis was used for comparison with the experimentally measured data and to determine the CM constants. Low cycle fatigue tests and FE simulations were carried out for these lead‐free solder joints, and eutectic Sn‐37Pb solder was used as a reference.Findings – The CM equation for Sn‐8Zn‐3Bi solder joints was fitted to the lifetimes measured and the shear strains simulated. The constants were determined to be 0.0294 for C, the proportional constant, and for the fatigue exponent, β, −2.833.Originality/value – The CM equation can now be used to predict the reliability of Sn‐8Zn‐3Bi solder joints in electronics assembly an...

Thermal cycling of lead-free Sn-3.8Ag-0.7Cu 388PBGA packages

Purpose – The purpose of this paper is to assess the effect of different temperature cycling profiles on the reliability of lead‐free 388 plastic ball grid array (PBGA) packages and to deeply understand crack initiation and propagation.Design/methodology/approach – Temperature cycling of Sn‐3.8Ag‐0.7Cu PBGA packages was carried out at two temperature profiles, the first ranging between −55°C and 100°C (TC1) and the second between 0°C and 100°C (TC2). Crack initiation and propagation was analyzed periodically and totally 7,000 cycles were run for TC1 and 14,500 for TC2. Finite element modeling (FEM), for the analysis of strain and stress, was used to corroborate the experimental results.Findings – The paper finds that TC1 had a characteristic life of 5,415 cycles and TC2 of 14,094 cycles, resulting in an acceleration factor of 2.6 between both profiles. Cracks were first visible for TC1, after 2,500 cycles, and only after 4,000 cycles for TC2. The crack propagation rate was faster for TC1 compared to TC2, ...

Flip-Chip Interconnection Using Anisotropic Conductive Adhesive with Lead Free Nano-Solder Particles

The flip-chip interconnections obtained using anisotropic conductive adhesives (ACA) containing nanoparticles of Sn-4.0Ag-0.5Cu and Sn-0.4Co-0.7Cu (wt% composition) lead free solder alloys as fillers were studied in order to make use of the nanosize effect in flip-chip interconnection applications. The ACAs were formulated using epoxy resin, curing agent, coupling agent and lead free solder nanoparticles. The filler content used in this study was 1wt%. The silicon chips with electroless nickel and immersion gold platted bumps, and FR-4 test boards with copper, nickel and gold platted pads were used in this work. The average contact resistances of the flip chip joints, measured by means of four probe measurement method were 7.08 mOmega and 6.69 mOmega for joints with Sn-4.0Ag-0.5Cu & Sn-0.4Co-0.7Cu nanoparticles respectively. As epoxy resins are hygroscopic in nature and they absorb water, pressure cooker test was carried out in order to study the effect of severe humidity and temperature on the integrity and reliability of nanointerconnects formed in flip chip packages. It was observed that after 24 hours of pressure cooker testing, there was a slight increase in contact resistance due to moisture absorption causing hygroscopic swelling which induced residual stresses in the package. The measured contact resistance values after the pressure cooker test were 10mOmega~32mOmega

Manufacture, microstructure and microhardness analysis of Sn-Bi lead-free solder reinforced with Sn-Ag-Cu nano-particles

This paper investigates a composite solders obtained by adding Sn-3.0Ag-0.5Cu (SAC) nano-particles into conventional eutectic Sn-58Bi solder paste. The microstructure analysis and the measurement of the Vickers microhardness have been carried out. Utilizing the self-developed consumable-electrode direct current arc (CDCA) technique, the Sn-3.0Ag-0.5Cu nano-particles with an average particle size between 20 and 80 nm are prepared. The reinforced lead-free Sn-Bi solder was prepared by thoroughly blending the nanometer-sized SAC particles into the eutectic Sn-Bi solder paste. The SAC reinforced Sn-Bi composite solder paste was printed onto ENIG/Cu metalized substrate and reflowed in a conventional reflow oven. After reflow, the morphology of the as-solidified reinforced composite solder was observed by means of SEM and TEM. The Vickers microhardness measurements indicated that the addition of SAC nano-particles enhances the overall strength of the eutectic solder, and the results agree well with the theory of dispersion strengthening.

Recent advances in the synthesis of lead-free solder nanoparticle

Particles in the nano-meter size range present extraordinary properties, such as, large surface area per unit volume, large surface energy, low melting point, supermagnetism, self-purification and quantum size effects. These properties have attracted the attention of scientific and technological communities al over the world.In the area of electronics production, one major disadvantage of conventional lead-free solders is their relatively high melting temperatures. Higher melting temperatures result in higher reflow temperatures which in turn result in stress build-up and other defects occurring during reflow. The possibility to lower the melting temperature of solder alloys and to improve the mechanical properties of solder joints by decreasing the particle size to the nanometer range, has therefore, offered a potential solution to these problems. Nanoparticles of different solder alloys have, therefore, been manufactured using both top-down and bottom-up techniques. This paper presents the latest developments in the area of lead-free solder nanoparticles manufacturing. Both the manufacturing and characterization of solder nanoparticles are covered. This paper does not include, however, applications of such nanoparticles. Both work performed in our group and in other research groups, from all over the world, is included, and the results discussed.