Reflow Temperature Research Articles

A Comparison Between Solders & Transient Liquid Phase Sintered Interconnects in High Temperature Multi-Layer Ceramic Capacitors

Abstract There is a long-established market for high temperature multi-layer ceramic capacitors (MLCC) that operate at 150°C and higher in down-hole oil & gas exploration, military and aerospace applications. To maximize the capacitance density and achieve a high degree of mechanical robustness, stacks and leaded form factors have been used with High Melting Point (HMP) Pb-containing solders as the preferred interconnects. However, Pb-containing solders are limited to temperatures below 300°C and are banned from many commercial and automotive applications with further legislation limiting their use planned in the future. Common Pb-free solders such as SAC 305 or SnSb alloys are in widespread use but their performance at prolonged exposures at 200°C is limited. Exposures to high reflow temperatures during assembly, especially successive reflow operations, can also compromise interconnect integrity. Higher temperature gold-containing solders are widely available but these are cost prohibitive and so are not viable for emerging high temperature electronics including higher volume, price sensitive Automotive and Power markets. The development of more energy efficient power converters and inverters based on Wide Band Gap (WBG) semiconductors is driving the adoption of higher temperature electronics in these markets since these operate at higher junction temperatures than traditional silicon. This has led to the development of non-solder interconnects based on sintered silver, nano-metal sintering and transient liquid phase sintering (TLPS) technologies capable of higher temperature performance than common solder based interconnects. The availability of discrete components, such as capacitors, that can operate under these conditions is a key barrier to the development and adoption of high temperature electronics. In this paper the key property differences between solders and TLPS interconnect technologies are compared in detail for MLCC interconnects. The development of a new range of nickel Base Metal Electrode C0G MLCC stacks rated for 200°C is described and performance compared to traditional Precious Metal Electrode (PME) stacks. Thermal cycling performance to 200°C of BME X7R stacks made with 10Sn/88Pb/2Ag solders are compared to similar stacks made with TLPS interconnects of Cu-Sn and In-Ag. The development of leadless stacks, a new bulk capacitance form factor enabled by TLPS technology, is described and their properties compared to traditional stacks.

Real-time profiling of reflow process in VPS chamber

PurposeThis paper aims to present a new method of real-time monitoring of thermal profiles applied in vapour phase soldering (VPS) reflow processes. The thermal profile setting is a significant variable that affects the quality of joints. The method allows rapid achievement of a required thermal profile based on software control that brings new efficiency to the reflow process and enhanced joint quality, especially for power electronics.Design/methodology/approachA real-time monitoring system based on computerized heat control was realized in a newly developed laboratory VPS chamber using a proportional integral derivation controller within the soldering process. The principle lies in the strictly accurate monitoring of the real defined reflow profile as a reference.FindingsVery accurate maintenance of the required reflow profile temperature was achieved with high accuracy (± 2°C). The new method of monitoring and control of the reflow real-time profiling was verified at various maximal reflow temperatures (230°C, 240°C and 260°C). The method is feasible for reflowing three-dimensional (3D) power modules that use various types of solders. The real-time monitoring system based on computerised heat control helped to achieve various heights of vapour zone.Originality/valueThe paper describes construction of a newly developed laboratory-scale VPS chamber, including novel real-time profiling of the reflow process based on intelligent continuously measured temperatures at various horizontal positions. Real-time profiling in the laboratory VPS chamber allowed reflow soldering on 3D power modules (of greater dimensions) by applying various flux-less solder materials.

Moisture Ingress, Behavior, and Prediction Inside Semiconductor Packaging: A Review

Reliability issues associated with moisture have become increasingly important as advanced electronic devices are nowhere more evident than in portable electronic products. The transition to the Pb-free solders, which require higher reflow temperature, makes the problem further exacerbated. Moisture absorbed into semiconductor packages can initiate many failure mechanisms, in particular interfacial delamination, degradation of adhesion strength, etc. The absorbed moisture can also result in catastrophic crack propagation during reflow process, the well-known phenomenon called popcorning. High vapor pressure inside pre-existing voids at material interfaces is known to be a dominant driving force of this phenomenon. This paper reviews various existing mechanisms of water accumulation inside voids. The procedures to obtain the critical hygroscopic properties are described. Advanced numerical modeling schemes to analyze the moisture diffusion phenomenon are followed with selected examples.

Effects of Complexing Reagent on Electroless Nickel Iron Alloy Plating for the Diffusion Barrier of UBM

Electro and electroless nickel platings have been extensively used as a diffusion barrier in under bump metallization (UBM) or as a surface finish on printed circuit boards (PCB). Even though a thin Ni layer on top of Cu can reduce the interfacial reactions with Sn-rich solders at a low reflow temperature, it may not be so effective when a reflow process is performed at a higher temperature and for a longer period. To provide a more robust diffusion barrier layer than electrodes Ni, electroless NiFe alloy system has been proposed. Since the electroless Ni-Fe plating bath has been rarely studied, the proper baths were not available commercially. In this research, the electroless plating of Ni-Fe alloys was investigated on the basis of complexing reagent. The stability of complexing reagent was studied. The compositions of electroplating layers were analyzed with EDS. The desired Ni-Fe alloy were obtained by controlling the chemical composition of the bath and its operating parameters.

Thin hybrid pixel assembly with backside compensation layer on ROIC

The entire ATLAS inner tracking system will be replaced for operation at the HL-LHC . This will include a significantly larger pixel detector of approximately 15 m2. For this project, it is critical to reduce the mass of the hybrid pixel modules and this requires thinning both the sensor and readout chips to about 150 micrometres each. The thinning of the silicon chips leads to low bump yield for SnAg bumps due to bad co-planarity of the two chips at the solder reflow stage creating dead zones within the pixel array. In the case of the ATLAS FEI4 pixel readout chip thinned to 100 micrometres, the chip is concave, with the front side in compression, with a bow of +100 micrometres at room temperature which varies to a bow of −175 micrometres at the SnAg solder reflow temperature, caused by the CTE mismatch between the materials in the CMOS stack and the silicon substrate. A new wafer level process to address the issue of low bump yield be controlling the chip bow has been developed. A back-side dielectric and metal stack of SiN and Al:Si has been deposited on the readout chip wafer to dynamically compensate the stress of the front side stack. In keeping with a 3D process the materials used are compatible with Through Silicon Via (TSV) technology with a TSV last approach which is under development for this chip. It is demonstrated that the amplitude of the correction can be manipulated by the deposition conditions and thickness of the SiN/Al:Si stack. The bow magnitude over the temperature range for the best sample to date is reduced by almost a factor of 4 and the sign of the bow (shape of the die) remains constant. Further development of the backside deposition conditions is on-going with the target of close to zero bow at the solder reflow temperature and a minimal bow magnitude throughout the temperature range. Assemblies produced from FEI4 readout wafers thinned to 100 micrometres with the backside compensation layer have been made for the first time and demonstrate bond yields close to 100%.

The Melting Characteristics and Interfacial Reactions of Sn-ball/Sn-3.0Ag-0.5Cu-paste/Cu Joints During Reflow Soldering

In this work, the melting characteristics and interfacial reactions of Sn-ball/Sn-3.0Ag-0.5Cu-paste/Cu (Sn/SAC305-paste/Cu) structure joints were studied using differential scanning calorimetry, in order to gain a deeper and broader understanding of the interfacial behavior and metallurgical combination among the substrate (under-bump metallization), solder ball and solder paste in a board-level ball grid array (BGA) assembly process, which is often seen as a mixed assembly using solder balls and solder pastes. Results show that at the SAC305 melting temperature of 217°C, neither the SAC305-paste nor the Sn-ball coalesce, while an interfacial reaction occurs between the SAC305-paste and Cu. A slight increase in reflow temperature (from 217°C to 218°C) results in the coalescence of the SAC305-paste with the Sn-ball. The Sn-ball exhibits premelting behavior at reflow temperatures below its melting temperature, and the premelting direction is from the bottom to the top of the Sn-ball. Remarkably, at 227°C, which is nearly 5°C lower than the melting point of pure Sn, the Sn-ball melts completely, resulting from two eutectic reactions, i.e., the reaction between Sn and Cu and that between Sn and Ag. Furthermore, a large amount of bulk Cu6Sn5 phase forms in the solder due to the quick dissolution of Cu substrate when the reflow temperature is increased to 245°C. In addition, the growth of the interfacial Cu6Sn5 layer at the SAC305-paste/Cu interface is controlled mainly by grain boundary diffusion, while the growth of the interfacial Cu3Sn layer is controlled mainly by bulk diffusion.

Fabrication of Cu@Sn Core-Shell Structured Particles and the Application in High Remelting Temperature Bonding

A novel solder bonding material for high-temperature applications based on Cu@Sn core-shell structured particles was developed, and the fabricated Cu@Sn particles were compressed into preforms for die attachment. The reflow temperature for this bonding material could reached as low as 260°C due to the low melting temperature of the outer Sn layer. However, after reflow soldering, the resulting interconnections can withstand a high temperature of at least 415°C, outer Sn layer completely transformed into Cu-Sn intermetallic compounds (IMCs) with high remelting temperatures. The formed bondlines exhibit good electrical conductivity due to the low porosity and the embedded Cu particles in the interconnections. Furthermore, the interconnections also exhibit excellent reliability under thermal shock cycling from-55°C to 200°C. This die attach material is suitable for power devices operating under high temperatures or other harsh environments.

Alternative Metallurgies for MEMS Lid Seal

Abstract MEMS devices are a segment of the electronics industry enjoying explosive growth. With the advent of the internet of things (IoT), the trajectory for growth will continue to be steep and price pressures on both the devices and packaging will be intense. Current MEMS packaging schemes rely heavily on an architecture that employs a metal-can or laminate “lid” attached to the device package with a solder ring. This ring serves to connect the package elements together mechanically and to protect the device from noise (electronic or acoustic) and environmental damage. Like most modern electronic devices, MEMS devices are subject to the challenges imposed by the requirement for lead-free packaging. As with many devices, solder connections formed within the package have a similar composition, and therefore a similar reflow profile, to the solder used to attach the packaged components to a substrate. Devices that yield well at the manufacturer are thus susceptible to field failure at the assembly site induced by remelting of the solder within the package during assembly reflow. Unlike in SIP packages where the solder joints in the module are often encased in mold compound, the ring seal in MEMS devices is exposed and unreinforced resulting in failures such as lid shift, solder flow or flux contamination in the device cavity, and package deconstruction - particularly during rework. These type of post-fabrication yield losses can be very costly. Transient liquid phase (TLPS) sintering paste compositions are a new class of solder replacement materials that can be processed at typical reflow temperatures, but which do not remelt when subjected to subsequent thermal excursions. TLPS pastes combine solder alloy particles and reactive metal particles in proportions such that the solder ‘thermosets’ during a typical solder reflow cycle. This ‘thermosetting’ behavior results in a joint that does not remelt at the original reflow temperature, and thus enables the highly reliable electrical interconnect essential for assemblies that will undergo subsequent reflow excursions. TLPS pastes are similar to solders in many respects. The electrical, thermal and mechanical performance is similar to conventionally used tin-based solders. The TLPS pastes are stored and applied like solder pastes. The reflow cycles used to form the TLPS paste joints are also similar to those for forming solder joints. However, unlike solder, TLPS materials do not change shape during reflow or wet substrates beyond the deposition footprint. Also unlike solder, the metals within the bulk of the TLPS interconnect react with one another resulting in a stable interconnect with a thermally robust bonding structure to joining surfaces, even after subsequent thermal cycles. These attributes present both unique opportunities and unique challenges for addressing MEMS lid seal applications. This paper will explore the key material and engineering challenges for implementation of TLPS paste in MEMS lid seal applications.

Voiding Control at Preform Soldering

Abstract Assembly of components with large pads such as high brightness LEDs or high power dies often is soldered with preform, mainly due to a lower voiding and lower flux fume generated when compared with solder paste, and also because of its better thermal and electrical conductivity compared with Ag epoxy. This is particularly true when the joints are to be formed within a cavity. Although lower than solder paste, the voiding in the solder joint is still a concern for high reliability and high performance devices. In this study, voiding at high power die attach reflow soldering using preform was simulated with the use of Cu coupons to mimic both die and substrate. The voiding behavior was studied by varying solder alloy type, flux quantity coated on preform, oxidation extent of Cu coupon, reflow peak temperature, and weight applied on the top of simulated die. For SAC305, with increasing weight, the bondline thickness (BLT) maintained constant initially due to solder surface tension, then reduced rapidly at weight higher than 50 g. The voiding area % increased with decreasing BLT first, then levelled off at lower BLT, although the voiding volume decreased with decreasing BLT due to constrained lamellar solder flow. Voiding was the highest for SAC305, followed by 57Bi42Sn1Ag, with 63Sn37Pb being the lowest, and increased with increasing oxidation of Cu coupon. With increasing flux quantity, voiding increased for SAC305 and 63Sn37Pb, but decreased for 57Bi42Sn1Ag, mainly due to the different temperature range at reflow. Voiding increased with increasing reflow temperature up to 170°C due to increasing vaporization, decreased with further increase in reflow temperature up to 210°C due to increasing flux activity, and increased again at temperature beyond 210°C due to rapid flux outgassing.

Effect of Chain Flexibility of Epoxy Encapsulants on the Performance and Reliability of Light-Emitting Diodes

Cycloaliphatic epoxy resin (3–4-epoxycyclohexane) methyl 3–4-epoxycyclohexyl-carboxylate (ECC) was formulated with flexible hydrogenated bisphenol A diglycidyl ether (HBADGE) to inspect the influence of chain flexibility on the performance and reliability of epoxy packaged Light-emitting Diode (LED). The properties of epoxy encapsulants were characterized by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), ultraviolet visible (UV–vis) spectrophotometer, thermomechanical analyzer (TMA), scanning acoustic microscopy (SAM), and scanning electron microscopy (SEM). With the incorporation of flexible HBADGE, favorable properties were obtained, such as decreased thermal expansion coefficient (CTE), lowered storage modulus at reflow temperature, and depressed equilibrium water uptake for the epoxy packaging materials. The light transmittance of encapsulants differed after thermal and UV aging. Compared with Neat ECC and Neat HBADGE, the HBADGE-mod...

Die attach materials with high remelting temperatures created by bonding Cu@Sn microparticles at lower temperatures

This paper presents a novel die attach material that withstands high working temperatures of up to 676°C after <40min of reflow at 250°C. The die attach material was preform compressed with Cu@Sn core-shell structured microparticles. When the reflow temperature reached 232°C, the outer Sn layer melted and connected the inner Cu cores. After reflow soldering at 250°C for 8min, the outer Sn completely transformed into network-like Cu-Sn intermetallic compounds (IMCs), which have a higher remelting temperature than Sn (415°C for Cu6Sn5 and 676°C for Cu3Sn). Consequently, the inner Cu cores were interconnected by the formed network-like Cu-Sn IMCs with a high remelting temperature of at least 415°C. If the sample was reflowed at 250°C for 40min, the outer Cu6Sn5 layer completely transformed into Cu3Sn, and the resulting bondline could sustain a higher temperature. The shear strengths of the resulting bondlines after reflow soldering at 250°C for 8 and 40min were 29.35 and 18.78MPa at 400 and 500°C, respectively.

Effect of fused silica surface wettability on thermal reflow of polymer microlens arrays

The objective of this study is to analyze the influence of substrate wettability and reflow conditions on the shape, lateral dimensions and optical properties of plano-convex lenses with nominal diameter of 16---28 µm fabricated by photolithographically patterning 7.5 µm thick layer of positive ma-P 1275 resist and subsequent thermal reflow. Five types of fused silica substrates modified by different plasma treatments and ion beam deposition of diamond like carbon (DLC) films were selected for the fabrication of microlens arrays in such a way that complete set of them could cover a wide range of wettability. At the same conditions of thermal reflow, defectivity of fabricated microlens arrays and resulting shape of the microlenses depended on the substrate treatment. Differences were especially marked for the lenses with smaller diameter. The best results were obtained for microlens arrays on DLC and SiOx doped DLC coated substrates. Minimal temperature required for complete reflow of the lenses with nominal diameter of 16---28 µm on SiOx doped DLC coated fused silica substrates depended on the lateral dimensions of the lenses and varied from 130 to 140 °C. Radius of curvature for the fabricated lenses could be somewhat tailored by the further increase of reflow temperature.

Control of edge bulge evolution during photoresist reflow and its application to diamond microlens fabrication

The authors present an empirical study of profile evolution of lithographically defined photoresist (PR) patterns during thermal reflow and apply the findings to diamond microlens fabrication. During PR reflow, a bulge forms at the edge of the PR pattern and propagates inwards as the temperature and PR thickness are increased. An empirical relationship for this propagation is derived. Furthermore, it was found that at a certain reflow temperature and a limited pattern size, there is a minimum initial thickness of the PR pattern for forming spherical lens profiles. Based on these findings, diamond microlenses with a diameter of 400 μm and a previously unachieved radius of curvature of over 13 mm were fabricated. This is underpinned by forming PR microlens patterns with a large radius of curvature and transferring the PR patterns through low-selectivity Ar/Cl2 inductively coupled plasma etching.

Improvements in Decision Making Criteria for Thermal Warpage

Surface mount components are commonly evaluated for out-of-plane warpage levels across reflow temperatures. Decision making for acceptable warpage levels is primarily made based on signed warpage levels of a single component surface, per industry standards. This paper discusses how a single signed warpage value is an oversimplified and incomplete way to describe a surface mount attachment between two mating surfaces that change in shape over temperature. Specific examples are shown where current industry standard gauges for thermal warpage are misleading. Issues include current industry standard equations for calculation of signed warpage. Optimal understanding of effects of warpage on surface mount attachment includes analysis of both mating surfaces under the same thermal and test conditions. Examples are shown of dual surface analysis, where gap between mating surfaces becomes the critical value in place of signed warpage. Evaluating both sides of two attaching surfaces is the optimal way to understand surface mount defects related to thermal warpage. However, many companies dealing with SMT will not have reasonable access to the surfaces to which their products will be attached. The paper goes on to discuss different approaches to more effectively quantify a single surface over temperature. This includes, but is not limited to, adding equations for signal strength values to currently established signed warpage standards.

Isothermal Aging of Low-Ag SAC with Al Addition

Zinc sulfide (ZnS) thin films have been successfully deposited via spray pyrolysis using an aqueous solution of thiourea and zinc Amongst the candidates of lead-free solders, eutectic or near eutectic Sn-Ag-Cu or SAC has been found to be the most suitable candidate to replace the traditional tin-lead (Sn-Pb) solder. However, due to the higher cost of SAC (expensive Ag), research have now been directed to find a lower cost lead-free solder with comparable or better performance to the Sn-Pb or SAC, i.e low Ag SAC or Sn-Cu solders. The solder alloys developed in this work were SAC 0305 (0.3 wt% Ag, 0.5 wt% Cu and bal. Sn) and SAC0305 with 1 wt% Al and 2 wt% Al. The addition of Al is expected to refine the β-Sn grains and contribute to higher solder strength. Characterization of the solder alloys focused on the bulk solder microstructure, intermetallic compound (IMC) evaluation and wettability of solder alloys in reflowed and aged conditions. Reflow temperature was 270°C while aging was done isothermally in normal atmosphere for 100, 200 and 500hours at 100°C and 150°C. Microstructure of bulk solder and the IMC formed at interface between solder and Cu substrate were observed using SEM equipped with EDX. Wettability of solder was evaluated via wetting force and time, and the wetting angle between solder and the Cu substrate. A low Ag content resulted in fine Ag3Sn IMC as compared to much larger needle Ag3Sn observed in the commercial SAC 305 (Ag 3.0 wt%). With Al addition, SEM result showed finer β-Sn dendrites with fine Ag3Sn and Cu6Sn5 distributed within the eutectic colony of the bulk solder, and also thinner IMC layer in reflowed samples. Isothermally aged samples on the other hand, showed thicker IMC layer for Al added solder samples. This could be attributed to the finer β-Sn dendrites in the bulk solder providing more diffusion path and increased the thickness of IMC layer. The IMC formed at the interface between solder and the copper substrate was identified as Cu6Sn5 in reflowed samples, and both Cu6Sn5 and Cu3Sn when aged. Wettability of the solder alloys decreased with the addition of Al.

Backward Compatibility Solder Joint Formation at High Peak Reflow Temperature for Aerospace Applications

This study investigates the backward compatibility solder joint formed at high peak reflow temperature in aerospace industries. The backward compatibility solder joint is made up of lead-free ball grid array mounted on printed circuit board using tin–lead solders at a maximum reflow temperature ranging from 241.9 to 242.45 °C. The reflow process was conducted under a nitrogen atmosphere in a full convection reflow oven for 80.12–81.27 s. The scanning electron microscopy cross section of the solder ball depicts fairly uniform composition and phase distribution of the Pb-free plastic ball grid array and the tin–lead solder paste across all joints. Nanoindentation tests showed better mechanical properties with higher elastic modulus at 68.64 GPa and acceptable hardness value at 0.26 GPa as compared to those of Sn–Pb and Pb-free solder balls. Intermetallic compound formation at both joints seen in the scanning electron microscopy shows a scallop shape and randomly directed growth because of the uniformly distributed Pb-rich phase on the solder ball. The average intermetallic compound thickness measured by scanning electron microscopy equipped with energy-dispersive X-ray analysis was 3.633 μm, which was less than the specified thickness of 12 μm from the laboratory request.

Low temperature In–Bi–Zn solder alloy on copper substrate

In this paper, characteristic of In–32.7Bi–0.5Zn lead-free solder system have been studied. DSC shows that, In–32.7Bi–0.5Zn system alloy give low melting temperature at 72.30 °C. Lowest melting temperature ensures that the solder melts, forms a joint with the substrates, and re-solidifies within the shortest possible process time. Further, the wettability between molten solder and copper substrate was measured at different reflow temperature. The contact angle for In–32.7Bi–0.5Zn solder alloys were decreasing 30.76° to 24.5° as the temperature increased from 100 to 140 °C. A significant increment of contact angle for In–32.7Bi–0.5Zn at 140 °C. The result of spreading area is inversed with the contact angle. Energy-dispersive X-ray analysis indicated two layer of intermetallic compound between the solder and the substrate; Cu5Zn8 and Cu11In9 compound.

Influence of latent heat released from solder joints on the reflow temperature profile

The reflow process of SAC305 solder paste was investigated by differential scanning calorimetry (DSC) and measurement of the temperature profiles in a real continual convection reflow furnace. Melting and solidification processes of two solder joints were investigated by both methods to determine the influence of latent heat on the surrounding temperature. While one peak was present during melting in DSC, two peaks were present during solidification of two joints connected by a resistor. The released latent heat from one joint increased the temperature of the surroundings and delayed the solidification process of the second joint. Analysis of the temperature profiles obtained during the reflow processes in a real furnace shows that latent heat influences the surrounding temperature not only during the phase transformation, but also during the whole following passage of the sample in the furnace. The maximum temperature increase of the joint is substantial: 25 mg of the solder paste increases the joint temperature by about 15 °C. When two joints are placed on the sample the temperature increase is close to 20 °C.

Transient Liquid Phase Sintering Pastes as Solder Alternatives in High Temperature Applications

High operating temperature electronics are a growing market in the electronics industry. Most of the components and substrates necessary to support the production of these harsh environment devices are now available, but the interconnect materials for component, module and board level assembly are lagging in development. Currently the high operating temperature markets are being served by lead-bearing solders and expensive alloys such as gold-tin or gold-germanium. Lead has been banned from the majority of electronics applications in many areas of the world, but so far has been exempted in the high temperature solder applications due to the lack of an adequate replacement. Even without the impending regulatory restrictions, the melting temperature of the lead containing solders is marginal for the next generation of high operating temperature electronics. Transient liquid phase (TLPS) sintering paste compositions are a new class of solder replacement materials that can be processed at typical reflow temperatures, but which do not remelt when subjected to subsequent thermal excursions. TLPS pastes combine solder alloy particles and reactive metal particles in proportions such that the solder ‘thermosets’ during a typical solder reflow cycle. This ‘thermosetting’ behavior results in a joint that does not remelt at the original reflow temperature, and thus enables the highly reliable electrical interconnect essential for high operating temperature applications. TLPS pastes are similar to solders in many respects. The electrical, thermal and mechanical performance is similar to conventionally used tin-based solders. The TLPS pastes are stored and applied like solder pastes. The reflow cycles used to form the TLPS paste joints are also similar to those for forming solder joints. However, unlike solder, TLPS materials do not change shape during reflow or wet substrates beyond the deposition footprint. Also unlike solder, the metals within the bulk of the TLPS interconnect react with one another resulting in a stable interconnect with a thermally robust bonding structure to joining surfaces, even after subsequent thermal cycles. Though not a practical replacement for solder in common assembly operations, TLPS technology is an attractive solder alternative for specialty interconnect applications. In this paper, the nature and characteristics of TLPS pastes will be will be explored in comparison to solder paste materials commonly used in high operating temperature applications.

Spreading Behaviour and Joint Reliability of Sn–0.3Ag–0.7Cu Lead-Free Solder Alloy on Nickel Coated Copper Substrate as a Function of Reflow Time

Solder joint directly interfaces electrically, mechanically and thermally with numerous electronic components in electronic assemblies. Sn–Ag–Cu lead-free solder alloys for electronic assembly are being driven by the environmental issues concerning the toxicity of lead. In the present study, spreading behaviour, evolution of intermetallic compounds during solidification of Sn–0.3Ag–0.7Cu solder alloy on Ni coated Cu substrate and the related joint strength were studied as a function of reflow time. Experiments were carried out for various reflow times of 10, 100, 300 and 500 s at a reflow temperature of 270 °C. The solder alloy exhibited improvement in wettability on the substrate at longer reflow times. An increase in the IMC (CuNi)6Sn5 thickness was observed for samples reflowed up to 300 s and the thickness decreased for samples reflowed for 500 s. IMC layer formed were about 0.3, 1.15, 2.03, 1.94 μm during 10, 100, 300 and 500 s of reflow time respectively. The joint shear test was performed to assess the integrity of the Sn–0.3Ag–0.7Cu solder solidified on Cu substrates. The maximum joint strength was observed for samples reflowed for 100 s.