Organic Solderability Preservative Research Articles

Reliability Analysis of Lead-Free Solder Joints with Solder Doping on Harsh Environment

Abstract This paper investigates the effect of long term isothermal aging and thermal cycling on the reliability of lead-free solder mixes with different solder compositions, PCB surface finishes, and isothermal aging conditions. A variety of surface mount components are considered, including ball grid arrays (BGAs), quad flat no-lead packages (QFNs) and 2512 Surface Mount Resistors (SMRs). 12 lead-free solder pastes are tested; for BGA packages these are reflowed with lead-free solder spheres of SAC105, SAC305 and matched doped solder spheres (“matched” solder paste and sphere composition). Three surface finishes are tested: Organic Solderability Preservative (OSP), Immersion Silver (ImAg), and Electroless Nickel Immersion Gold (ENIG). All test components are subjected to isothermal aging at 125°C for 0 or 12 months, followed by accelerated thermal cycle testing from −40°C to 125°C. Data from the first 1500 cycles is presented here, with a focus on the effect of surface finish on package reliability. Current results demonstrate that the choice of surface finish has a strong effect on reliability. However, different solder materials appear to show different reliability trends with respect to the surface finishes, and the reliability trends of BGA and SMR packages also diverge.

Effect of Plasma Surface Finish on Wettability and Mechanical Properties of SAC305 Solder Joints

The wetting behavior, interfacial reactions, and mechanical reliability of Sn-Ag-Cu solder on a plasma-coated printed circuit board (PCB) substrate were evaluated under multiple heat-treatments. Conventional organic solderability preservative (OSP) finished PCBs were used as a reference. The plasma process created a dense and highly cross-linked polymer coating on the Cu substrates. The plasma finished samples had higher wetting forces and shorter zero-cross times than those with OSP surface finish. The OSP sample was degraded after sequential multiple heat treatments and reflow processes, whereas the solderability of the plasma finished sample was retained after multiple heat treatments. After the soldering process, similar microstructures were observed at the interfaces of the two solder joints, where the development of intermetallic compounds was observed. From ball shear tests, it was found that the shear force for the plasma substrate was consistently higher than that for the OSP substrate. Deterioration of the OSP surface finish was observed after multiple heat treatments. Overall, the plasma surface finish was superior to the conventional OSP finish with respect to wettability and joint reliability, indicating that it is a suitable material for the fabrication of complex electronic devices.

Galvanic corrosion of Cu coupled to Au on a print circuit board; Effects of pretreatment solution and etchant concentration in organic solderability preservatives soft etching solution

In present study, we quantitatively define the galvanic corrosion phenomenon of Cu electrically coupled to Au on Print Circuit Board in Organic Solderability Preservatives (OSP) pretreatment (pickling and soft etching) solutions. As a result of polarization and ZRA test, galvanic corrosion rate of Cu in soft etching solution was about 3000 times higher than that of pickling solution. The oxone in OSP soft etching solution was acted as strong oxidant for Cu on PCB substrate. And the galvanic corrosion of Cu in OSP soft etching solution was examined with the change of etchants (oxone (KHSO5), sulfuric acid (H2SO4)) concentration. The galvanic corrosion rate of Cu was increased by the increase of the oxone and sulfuric acid concentrations, which lead to the increase of cathodic reactant such as HSO5- and H+ ions. And the degree of galvanic corrosion rate of Cu (Δisoft etching = icouple, (Cu-Au) - icorr, Cu) decreased with the decrease of the oxone and sulfuric acid concentrations.

Al and Si Alloying Effect on Solder Joint Reliability in Sn-0.5Cu for Automotive Electronics

To suppress the bonding strength degradation of solder joints in automotive electronics, we proposed a mid-temperature quaternary Pb-free Sn-0.5Cu solder alloy with minor Pd, Al, Si and Ge alloying elements. We manufactured powders and solder pastes of Sn-0.5Cu-(0.01,0.03)Al-0.005Si-(0.006–0.007)Ge alloys (Tm = 230°C), and vehicle electronic control units used for a flame-retardant-4 printed circuit board with an organic solderability preservative finish were assembled by a reflow soldering process. To investigate the degradation properties of solder joints used in engine compartments, thermal cycling tests were conducted from −40°C to 125°C (10 min dwell) for 1500 cycles. We also measured the shear strength of the solder joints in various components and observed the microstructural evolution of the solder joints. Based on these results, intermetallic compound (IMC) growth at the solder joints was suppressed by minor Pd, Al and Si additions to the Sn-0.5Cu alloy. After 1500 thermal cycles, IMC layers thicknesses for 100 parts per million (ppm) and 300 ppm Al alloy additions were 6.7 μm and 10 μm, compared to the as-reflowed bonding thicknesses of 6 μm and 7 μm, respectively. Furthermore, shear strength degradation rates for 100 ppm and 300 ppm Al(Si) alloy additions were at least 19.5%–26.2%. The cause of the improvement in thermal cycling reliability was analyzed using the (Al,Cu)-Sn, Si-Sn and Al-Sn phases dispersed around the Cu6Sn5 intermetallic at the solder matrix and bonding interfaces. From these results, we propose the possibility of a mid-temperature Sn-0.5Cu(Pd)-Al(Si)-Ge Pb-free solder for automotive engine compartment electronics.

Failure analysis of printed circuit boards in the main telephone system of marine product factory

The failure of the main telephone system in a marine product factory due to copper sulfide (Cu2S) creep was analyzed by the measurement of hydrogen sulfide (H2S) in the atmosphere, elemental analysis with energy dispersive X-ray spectroscopy, and cross-sectional observation of vias in the printed circuit boards. Indoor H2S concentrations were higher than outdoor ones and these corresponded to the G2 and/or G3 levels defined in ISA S71.04-1985. The chemical composition of the copper sulfide creep indicates that it consisted of copper, oxygen, and sulfur. Cross-sectional observation and elemental mapping analysis showed that Cu2S creep initiated not at the edge of the organic coating (organic solder preservative, OSP) inside the vias but mainly at defects in the organic coating covering the copper.

Board Level Drop Reliability of Epoxy-Containing Sn-58 mass% Bi Solder Joints with Various Surface Finishes

Board-level drop reliability testing under JEDEC (Joint Electron Device Engineering Council) drop conditions was conducted for low-temperature Sn-58 mass%Bi solder joints. The effects of surface finish and the number of reflow processes (one, three, or five) on the drop reliability of the Sn-58Bi joints were evaluated. Three types of surface finishes were used including electroless nickel immersion gold (ENIG), electroless nickel electroless palladium immersion gold (ENEPIG), and organic solderability preservatives (OSP). We successfully fabricated six types of drop test specimens with various surface finishes and bonding materials, and then performed the board-level drop tests. The board-level drop reliability was improved when using the composite Sn-58Bi solder with epoxy as compared to Sn-58Bi solder without epoxy. In addition, the reliability of the Sn-58Bi epoxy solder/OSP joint was better than both the ENIG and ENEPIG surface finishes. When the number of reflow processes increased, the drop reliability showed two different behaviors; specifically, the reliability of the ENIG and ENEPIG surface finishes decreased while the OSP surface finish improved. The existence of epoxy in the solder paste improved the drop reliability of the solder joints. After drop testing, cracks propagated differently with different surface finishes, namely between Ni3Sn4 IMCs and the Ni-P layer for the ENIG surface finish, between Ni3Sn4 IMCs and the solder bulk for the ENEPIG surface finish, and within the solder bulk for the OSP surface finish. These data show that, when it is necessary to perform repeated reflow processes for electronic components, solder joints with an OSP surface finish provide better drop test reliability results.

Electromigration effect on Sn-58 % Bi solder joints with various substrate metallizations under current stress

The electromigration behavior of low-melting temperature Sn-58Bi (in wt%) solder joints was investigated with a high current density between 3 and 4.5 × 103 A/cm2 between 80 and 110 °C. In order to analyze the impact of various substrate metallizations on the electromigration performance of the Sn-58Bi joint, we used representative substrate metallizations including electroless nickel immersion gold (ENIG), electroless nickel electroless palladium immersion gold (ENEPIG), and organic solderability preservatives (OSP). As the applied current density increased, the time to failure (TTF) for electromigration decreased regardless of the temperature or substrate metallizations. In addition, the TTF slightly decreased with increasing temperature. The substrate metallization significantly affected the TTF for the electromigration behavior of the Sn-58Bi solder joints. The substrate metallizations for electromigration performance of the Sn-58Bi solder are ranked in the following order: OSP-Cu, ENEPIG, and ENIG. Due to the polarity effect, current stressing enhanced the fast growth of intermetallic compounds (IMCs) at the anode interface. Cracks occurred at the Ni3Sn4 + Ni3P IMC/Cu interfaces on the cathode sides in the Sn-58Bi/ENIG joint and the Sn-58Bi/ENEPIG joint; this was caused by the complete consumption of the Ni(P) layer. Alternatively, failure occurred via deformation of the bulk solder in the Sn-58Bi/OSP-Cu joint. The experimental results confirmed that the electromigration reliability of the Sn-58Bi/OSP-Cu joint was superior to those of the Sn-58Bi/ENIG or Sn-58Bi/ENEPIG joints.

Effects of Ag content on the reliability of LED package component with Sn–Bi–Ag solder

The effects of Ag content on the mechanical and electrical properties of the Sn–58Bi solder joints in light emitting diode (LED) package were studied. The Sn–58Bi, Sn–57.6Bi–0.4Ag and Sn–57Bi–1Ag solder were used as solder joints. The LED package was bonded on the printed circuit board (PCB) with the organic solderability preservative (OSP) surface finish, and then it was aged at 85 °C for 100, 300, 500 and 1000 h, respectively. In order to evaluate the mechanical and electrical properties, the shear test was conducted and the change of current versus voltage was measured. The shear strength and electrical conductivity of solder joints decreased with an increasing aging time. With an addition of 1.0 wt% Ag, the shear strength was improved and higher than those of other solder joints. The microstructure and composition of the solder joints were investigated with a scanning electron microscope, an energy dispersive spectrometer and an electron probe micro analyzer. The Cu6Sn5 intermetallic compounds (IMCs) formed between solder and OSP surface finished Cu pad of PCB. The thickness of the IMCs increased with an increasing aging time. By an addition of 0.4 wt% Ag, fine Ag3Sn particles were dispersed inside the solder matrix and large-sized primary Ag3Sn IMCs were formed with 1.0 wt% Ag addition.

Effect of Electromigration on the Type of Drop Failure of Sn–3.0Ag–0.5Cu Solder Joints in PBGA Packages

Board-level drop tests of plastic ball grid array (PBGA) packages were performed in accordance with the Joint Electron Devices Engineering Council standard to investigate the effect of electromigration (EM) on the drop reliability of Sn–3.0Ag–0.5Cu solder joints with two substrate surface finishes, organic solderability preservative (OSP) and electroless nickel electroless palladium immersion gold (ENEPIG). In the as-soldered state, drop failures occurred at the substrate sides only, with cracks propagating within the interfacial intermetallic compound (IMC) layer for OSP solder joints and along the IMC/Ni–P interface for ENEPIG solder joints. The drop lifetime of OSP solder joints was approximately twice that of ENEPIG joints. EM had an important effect on crack formation and drop lifetime of the PBGA solder joints. ENEPIG solder joints performed better in drop reliability tests after EM, that is, the drop lifetime of ENEPIG joints decreased by 43% whereas that of OSP solder joints decreased by 91%, compared with the as-soldered cases. The more serious polarity effect, i.e., excessive growth of the interfacial IMC at the anode, was responsible for the sharper decrease in drop lifetime. The different types of drop failure of PBGA solder joints before and after EM, including the position of initiation and the propagation path of cracks, are discussed on the basis of the growth behavior of interfacial IMC.

Interfacial reaction and failure mode analysis of the solder joints for flip-chip LED on ENIG and Cu-OSP surface finishes

The interfacial reactions and failure modes of the solder joints for flip-chip light emitting diode (LED) on electroless nickel/immersion gold (ENIG) and Cu with organic solderability preservatives (Cu-OSP) surface finishes were investigated in this study. The experimental results demonstrate that the interfacial reactions in the Au/Sn–Ag–Cu(SAC)/ENIG and Au/SAC/Cu systems are different but the failure mechanisms of the two types of solder joints are similar during the shear test. For the Au/SAC/ENIG system, the Au layer on the surface finish of the diodes dissolved into the molten solder and transformed into a continuous (Au, Ni)Sn4 IMC layer at the diode/solder interface during reflow and the interfacial IMC at the solder/ENIG interface is dendritic Ni3Sn4 IMC grains which are surrounded by (Au, Ni)Sn4. For the Au/SAC/Cu system, however, no IMC layers can be observed at the diode/solder interface. The interfacial IMC at the solder/Cu interface is (Cu, Au)6Sn5 and a Cu3Sn IMC layer at the (Cu, Au)6Sn5/Cu interface. Tiny (Au, Cu)Sn4 IMC grains distribute in the solder layer and surround the (Cu, Au)6Sn5 grains. For the two types of systems, the primary failure mode for the cathode is due to the broken of the Si-based insulation layer which led to a high residue stress and poor connection between the Si-based layer and the solder layer. Meanwhile, the failure of the solder joint for the anode is mainly because of the failure of the solder layer under the conductive via. The crack generally forms at this area and then propagated along the diode or the diode/solder interface.

New Failure Mode of Flip-Chip Solder Joints Related to the Metallization of an Organic Substrate

We report a new failure phenomenon during flip-chip die attach. After reflow, flip-chip bumps were separated between the Al and Ti layers on the Si die side. This was mainly observed at the Si die corner. Transmission electron microscopy images revealed corrosion of the Al layer at the edge of the solder bump metallization. The corrosion at the metallization edge exhibited a notch shape with high stress concentration factor. The organic substrate had Cu metallization with an organic solderable preservative (OSP) coating layer, where a small amount of Cl ions were detected. A solder bump separation mechanism is suggested based on the reaction between Al and Cl, related to the flow of soldering flux. During reflow, the flux will dissolve the Cl-containing OSP layer and flow up to the Al layer on the Si die side. Then, the Cl-dissolved flux will actively react with Al, forming AlCl3. During cooling, solder bumps at the Si die corner will separate through the location of Al corrosion. This demonstrated that the chemistry of the substrate metallization can affect the thermomechanical reliability of flip-chip solder joints.

Wetting behaviour of SAC305 solder on different substrates in high vacuum and inert atmosphere

The wettability between solder and substrate is a very important issue in reliability of soldering process. The contact angle θ is used to measure the degree of wetting. The contact angle of lead-free alloy Sn-3 % Ag-0.5 % Cu (wt%) was measured, as a function of temperature, for three different commercial surface finish substrates used in printed circuit boards (PCB): Sn, NiAu and Organic Solderability Preservative (OSP). The measurements were performed by the sessile drop method in two different atmospheres: high vacuum and inert gas. In high vacuum the results showed that on substrates of NiAu and OSP the solder started spreading suddenly at 225 °C and in Sn substrate the contact angle decreases slightly with temperature. In inert gas atmosphere the results showed different behaviours: the contact angle between molten solder in OSP and NiAu substrates is sensitive to temperature; and, in Sn substrate, the contact angle does not change with temperature. The NiAu and OSP substrates showed a better degree of wettability than Sn substrate, in inert atmosphere.

Investigation of Wettability of Lead Free-Solder on Bare Copper and Organic Solder Preservatives Surface Finishes

Wettability plays an important role in the integrity of solder joints especially in critical safety operations. It helps in attaining successful soldering and reliable solder joints. The angle of wettability determines the degree of solder contact and strength of the solder joint. Moreover, the contact angle between the solid substrate and the molten solder determines the interconnection reliability. This paper focuses on the wettability of lead free solder on OSP and bare copper substrate surface finishes. The wetting behaviour of lead free solder pastes on bare copper board and Organic Solderability Preservatives (OSPs) substrates were investigated. The test vehicles consist of FR4 PCB single sided 100% copper clad with a thick film metallization and FR4 PCB single sided OSP. The substrate dimension was 100 mm×160 mm×1.6 mm. A total of 480 bumps of Lead-free solder pastes (96Sn-3.8Ag-0.5Cu and 96.5Sn-3.0Ag-0.7Cu alloy composition) were deposited for the investigation. The printing parameters and their values for the experiments include print gap of 0 mm, squeegee speed of 20 mm/s, pressure of 8kg and separation speed of 3 mm/sec. The pastes are screen printed on the substrates using 0.125mm thick stencil mounted on DEK 260 series printing machine. After the stencil printing process, the solder bumps deposited on the substrates were reflowed using a Novostar 2000HT horizontal convention reflow oven with 4-stage (preheat-soak-reflow-cooling). The FTA188 Analyser was employed for measuring the angle of contact between the substrates and the bumps. The results showed that the wetting contact angle of copper surface finish is lower as compared to the organic solderability preservatives surface finish and the wetting angle decreases as the contact surface area increases.

Sn-58Bi Solder와 OSP 표면 처리된 PCB의 접합강도에 미치는 시효처리와 에폭시의 영향

다양한 무연솔더합금 가운데 Sn-58Bi solder는 저융점이며 상대적으로 높은 인장강도를 갖고 있지만 취성적이라는 단점을 갖고 있다. 이러한 Sn-58Bi 솔더의 기계적 강도를 보완하기 위해 epoxy를 함유한 Sn-58Bi 솔더가 연구되어져왔다. 본 연구는 Sn-58Bi 솔더와 Sn-58Bi 에폭시 복합솔더를 이용하여 PCB 기판에 접합한 후, 시효처리에 따른 솔더/기판 계면 미세구조와 기계적 특성변화를 연구하였다. OSP 표면처리된 PCB 기판에 솔더볼을 형성 한 후 85, 95, 105, <TEX>$115^{\circ}C$</TEX>에서 100~1000 시간동안 시효처리하였으며, 기계적 특성평가로 저속전단시험을 진행하였다. 시효 처리 시간 및 온도의 증가에 따라 Cu6Sn5 금속간화합물층은 성장하였으며 Sn-58Bi 솔더 금속간화합물층이 Sn-58Bi 에폭시 복합솔더보다 두꺼웠다. 전단시험 결과, Sn-58Bi 에폭시 복합솔더가 Sn-58Bi 솔더보다 약 2배 높은 전단강도 값을 나타냈으며 시효시간이 증가할수록 전단강도 값은 감소하였다. Among various lead-free solders, the Sn-58Bi solders have been considered as a highly promising lead-free solders because of its low melting temperature and high tensile strength. However, Sn-58Bi solder has the poor ductility. To enhance the mechanical property of Sn-58Bi solder, epoxy-enhanced Sn-58Bi solders have been studied. This study compared the microstructures and the mechanical properties of Sn-58Bi solder and Sn-58Bi epoxy solder with aging treatment. The solders ball were formed on the printed circuit board (PCB) with organic solderability preservative (OSP) surface finish, and then the joints were aged at 85, 95, 105 and <TEX>$115^{\circ}C$</TEX> for up to 100, 300, 500 and 1000 hours. The shear test was conducted to evaluate the mechanical property of the solder joints. <TEX>$Cu_6Sn_5$</TEX> intermetallic compound (IMC) layer grew with increasing aging time and temperature. The IMC layer for the Sn-58Bi epoxy solder was thicker than that for the Sn-58Bi solder. According to result of shear test, the shear strength of Sn-58Bi epoxy solder was higher than that of Sn-58Bi solder and the shear strength decreased with increasing aging time.

Interfacial reaction and mechanical properties between low melting temperature Sn–58Bi solder and various surface finishes during reflow reactions

Interfacial reactions and joint mechanical reliability of a representative low melting temperature Sn–58 wt%Bi solder with three different surface finishes were evaluated during a reflow process. The surface materials consisted of organic solderability preservative (OSP), electroless nickel–immersion gold (ENIG), and electroless nickel–electroless palladium–immersion gold (ENEPIG). The relationships between the interfacial reaction, surface finish, shear speed, and shear force were elucidated in this study. The interfacial intermetallic compounds (IMCs) on the ENEPIG substrate were sequentially changed during reflowing at 180 °C in the following order: (Pd,Ni)Sn4, (Pd,Ni)Sn4 + Ni3Sn4, and Ni3Sn4. Compared to the Cu6Sn5 IMC on the OSP-finished Cu substrate, the Ni3Sn4 IMCs on the ENIG and ENEPIG substrates were much thinner. The IMCs of each of the different surface finishes grew as the reflow time increased; however, the morphologies of the IMCs were different each other. Layer-type interfacial IMCs created a stable metallurgical interfacial structure during the reflow reaction, resulting in reduced rates of IMC growth and Ni–P consumption. High-speed shear tests were conducted to evaluate the effects of interfacial reactions on the mechanical properties of three Sn–58Bi solder joints. In spite of the different interfacial reactions and IMC formations, there were no large differences among shear forces in the three Sn–58Bi solder joints. Further, the type of surface finish material did not significantly affect the shear force of the Sn–58Bi solder joints under high-speed shear loading.

Study of solder jet bumping process using high-speed digital camera

With the development of solder jet technology in the electronic packaging industry, the bumping process of a molten metal droplet, which determines the shape of the solder bump and is crucial for the performance of the device, has attracted great interests. The solder bumping process of a single molten micro-droplet by a solder jet was recorded using a high-speed digital camera with a frame rate of 100,000 frames per second. It was found that the surface ripples on the solder bump was caused by the interaction of the fluid flow and the heat transfer/solidification processes in the bumping process of a micro-droplet. A droplet was observed to rebound on a copper pad coated with a layer of organic solderability preservatives, which was suspected to decrease the interfacial heat transfer coefficient between the droplet and the pad lower than a minimal value, 4.07×104W/m2K, making the recoiling droplet rebound away.

Microstructure, thermal analysis and damping properties of Ag and Ni nano-particles doped Sn–8Zn–3Bi solder on OSP–Cu substrate

This paper investigates the effects of reaction time and temperature on the morphology and growth mechanism of intermetallic compound (IMC) layers of plain Sn–8Zn–3Bi solder and solders containing Ag, Ni nano-particles on Organic Solderability Preservative (OSP)–Cu substrate. At the interface of the plain Sn–8Zn–3Bi solder/OSP–Cu system, a scallop-shaped Cu5Zn8 IMC layer was clearly observed. However, after adding Ag nano-particles into the Sn–8Zn–3Bi solder, an additional island-type AgZn3 IMC layer was found at the top surface of the scallop-shaped Cu5Zn8 IMC layer. Moreover, in the Sn–8Zn–3Bi–0.5Ni solder/OSP–Cu system, a ternary (Cu, Ni)–Zn IMC layer was well adhered at their interfaces. Furthermore, in solder ball regions a needle-shaped α-Zn and spherically-shaped Bi phases were clearly observed in the β-Sn matrix of plain Sn–8Zn–3Bi solder. However, in the solder alloys containing Ag and Ni nano-particles an additional very fine AgZn3 IMC particles for Ag doped solder and Zn–Ni IMC particles for Ni doped solder was uniformly distributed as well as the needle-shaped α-Zn and spherically-shaped Bi phases in the β-Sn matrix. These IMC layer thicknesses were increased with the reaction time and temperature. However, after the addition of the Ag and Ni nano-particles, the IMC growth behavior was slower than that of the plain solder system.Damping capacity of plain Sn–8Zn–3Bi solder alloy and solder alloys containing Ag, Ni nano-particles were measured by dynamic mechanical analyzer (DMA). The damping capacity of composite solder alloys exhibited higher values than that of plain Sn–8Zn–3Bi solder alloy which is essential to suppress the mechanical vibration and wave propagation. Furthermore, the composite solder alloys doped with Ag, Ni nano-particles improved the oxidation resistance than that of plain Sn–8Zn–3Bi solder alloy by the formation of fine Zn containing IMC particles which block the penetration of vapor and oxygen into the solder matrix.

Effects of PCB ENIG and OSP Surface Finishes on the Electromigration Reliability and Shear Strength of Sn-3.5Ag PB-Free Solder Bump

The effects of printed circuit board electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP) surface finishes on the electromigration reliability and shear strength of Sn-3.5Ag Pb-free solder bump were systematically investigated. In-situ annealing tests were performed in a scanning electron microscope chamber at 130, 150, and <TEX>$170^{\circ}C$</TEX> in order to investigate the growth kinetics of intermetallic compound (IMC). Electromigration lifetime and failure modes were investigated at <TEX>$150^{\circ}C$</TEX> and <TEX>$1.5{\times}10^5A/cm^2$</TEX>, while ball shear tests and failure mode analysis were conducted under the high-speed conditions from 10 mm/s to 3000 mm/s. The activation energy of ENIG and OSP surface finishes during annealing were evaluated as 0.84 eV and 0.94 eV, respectively. The solder bumps with ENIG surface finish showed longer electromigration lifetime than OSP surface finish. Shear strengths between ENIG and OSP were similar, and the shear energies decreased with increasing shear speed. Failure analysis showed that electrical and mechanical reliabilities were very closely related to the interfacial IMC stabilities.

Study of Compatibility of Silicone-based Electrically Conductive Adhesives and Conductive Backsheets for MWT Modules

We investigate the compatibility of silicone-based electrically conductive adhesives and different surface finishes of the conductive backsheet (CBS) used in MWT module assembly technology. We find that the same ECA can lead to dramatically different properties of the electrical contact depending on the kind of surface finish. On lower cost surface finishes, such as those based on Organic Solderability Preservative, it is more challenging to achieve a low ohmic and stable contact using an ECA. Nevertheless, a silicone-based ECA, called Dow Corning® PV-5802, was developed that leads to excellent performance (low cell-to-module losses) and durability as evidenced by mini-modules passing 2000hours of damp heat and 600 thermal cycles.

Comparison of Ball Pull Strength Among Various Sn-Cu-Ni Solder Joints With Different Pad Surface Finishes

SnCuNi is one of the most common ternary intermetallic compounds formed in the Sn-based solder joint, and its formation and properties can be greatly influenced by the amount of Ni. Ni can participate in the interfacial reaction and diffuse into the intermetallic compound layer from either the solder or from the pad. In this research, comparative studies of different SnCuNi intermetallic compounds were conducted using two kinds of SnCuNi solders with organic solderability preservatives pad finish and a SnCu solder with electroless nickel/immersion gold pad finish. In the former case, Ni can only diffuse into the intermetallic compound from the solder matrix, while in the latter the Ni is only from the metallization layer on the Cu base. Scanning electron microscopy and transmission electron microscopy were employed to inspect the morphologies and interfacial microstructures of the intermetallic compounds. The thermal aging test was conducted to investigate their growth behavior under elevated temperature conditions. Mechanical strength after different aging hours was also evaluated via high speed ball pull test.