Solder Resist Research Articles

Synergistic effect of thermomigration and electric current stressing on damping capacity of Sn58Bi solder

In order to evaluate the vibration resistance of Sn58Bi solder in serving electronic devices, the damping capacities of Sn58Bi solders after thermomigration (TM) test at a temperature gradient of 2000 °C/cm for different time (0, 120, 360, 720, and 1440 h) were characterized under electric current stressing (0, 4.0, and 8.0 A). The results indicate that the phase segregation of TM-tested Sn58Bi solders determines the damping performance of solders. The Bi-rich layer thickens with prolonged TM time and migrates in the direction from high temperature to low temperature. Both the critical strains (the values of dislocation getting rid of pining points) of strain-amplitude-related damping capacity curves increases with prolonged TM time, while decreases with increasing electric current. Moreover, both strain-amplitude-related and temperature-related damping capacity shows a general decreasing trend with prolonged TM time, while increases exponentially with increasing electric current. In addition, the damping mechanism changes from dislocation motion to phase boundary sliding with increasing temperature, and the transition temperature decreases with increasing current but generally increases with TM time.

A strategy to prepare high Tg and low CTE solder resist using alkali-soluble photosensitive polyimide

Photosensitive Solder resist (SR) materials require a high glass transition temperature (Tg > 170 °C) and a coefficient of thermal expansion matching that of copper (CTE≈17 ppm/°C) to meet the demands of manufacturing processes and application reliability. However, the commonly used epoxy resin in SR materials exhibits insufficient mechanical and thermal properties, failing to meet these requirements adequately. To address this issue, alkali-soluble photosensitive poly (amic ester) (PAE) materials were synthesized. By grafting a low-temperature curing accelerator, 6-([1,1′-biphenyl]–4-yl)–4-chloroquinoline (NQL), onto the hydroxyl groups of the PAE, the resultant grafted PAE resin was blended with an alkali-soluble photosensitive modified epoxy resin (APE) to enhance the mechanical and thermal properties of the SR composite. Research indicates that due to the low-temperature curing effect and electrostatic interactions of NQL, SR-2 (with a 10 % PAE addition) exhibits a Tg of 183 °C and a CTE of 16 ppm/°C, while SR-3 (with a 30 % PAE addition) achieves a Tg of 204 °C and a CTE of 20 ppm/°C. Furthermore, with the PAE addition of 5 %, the lithography quality of SR is enhanced, enabling SR-1 to achieve a pattern resolution of up to 40 μm. The modification method involving PSPI blending has been shown to enhance the thermal stability, dimensional stability, and lithographic performance of SR, indicating significant potential applications in solder resist materials.

High-Adhesion Epoxy-Based Solder Resist Dry Film for Integrated Circuits Enhanced by 2,2-Bis(hydroxymethyl)propionic Acid

High-Adhesion Epoxy-Based Solder Resist Dry Film for Integrated Circuits Enhanced by 2,2-Bis(hydroxymethyl)propionic Acid

Design of Ni-rGO reinforced Sn2.5Ag0.7Cu0.1Ce composite solder based on micro-alloying and composite principles: Microstructure and properties

Based on the principles of micro-alloying and composite, the graphene reinforced Sn2.5Ag0.7Cu0.1Ce composite solder was designed. Ni nanoparticle-modified reduced graphene oxide (Ni-rGO) was prepared by thermal decomposition method, and the powder-melting method was proposed for the first time to prepare Ni-rGO reinforced Sn2.5Ag0.7Cu0.1Ce composite solder. The microstructure, wettability, electrical resistivity, and mechanical properties of the composite solder were systematically studied. Results indicated that the Ni nanoparticles uniformly adhered to the rGO with a size of 26.3 nm. The effective incorporation of Ni-rGO into the solder matrix was achieved. The result broke the technical difficulty that graphene cannot be effectively added to low melting point metals. With the addition of Ni-rGO, the grain size gradually decreased, and the eutectic structures increased. Deep etching results revealed that columnar β-Sn was stacked from layered β-Sn, the addition of 0.05 wt% Ni-rGO led to an increase in sheet-like Ag3Sn within the eutectics. Additionally, Ni-rGO was found at the grain boundaries of composite solder, serving as nucleation sites for Ag3Sn and Cu6Sn5. At an addition of 0.05 wt%, the tensile strength reaches a maximum of 58.1 MPa, with elongation of 33.8%, surpassing the strength of commercial Sn3.0Ag0.5Cu solder. Therefore, the high-strength and tough composite solder was obtained. This study offered a new approach for the development of low-melting-point composite materials.

High-performing naphthalene-type photocurable resin: Tailored properties by the selection of di-functional acid chain extenders

Despite the significant progress in high thermal-resisting photocurable resin, the simultaneous achievement of robustness, stretchability, and dielectric properties in modified naphthalene-type photocurable resin remains a great challenge owing to intrinsic restrictions mediated by strong π-π stacking effect. Herein, a simple and feasible method is demonstrated to respectively introduce three selected di-functional acid chain extenders into 1,6-naphthalene diglycidyl ether (NDE), and prepare a series of naphthalene-type photocurable enhancement resin with excellent thermal/mechanical properties and low dielectric traits. Most importantly, the effect of the increase of succinic acid (SA) chain-extending segments on the thermal and mechanical properties of SA chain-extending NDE (S-NDE) resin is systematically investigated. An optimized synthesized route is presented by chain extension chemical strategy, which enables the improvement of the “seesaw” issue between high heat resistance and mechanical robustness. As a consequence, the optimized UV-curing S-NDE thin film exhibits robust tensile strength (75.45 ± 4.46 MPa), excellent heat resistance (Tg: 145.4 °C), high stretchability (7.22 ± 0.85 %), and desired dielectric constant (2.2). Meanwhile, the uncured S-NDE resin exhibited an excellent alkali elution property within 5 min. An actually printed circuit board (PCB) solder resistance coating/patterning application is further demonstrated based on the selective elution property of high-performance formulated S-NDE green ink, providing an efficient strategy for the design and fabrication of high-performance naphthalene-type photocurable materials.

Rational design and coloration mechanism of soluble intrinsic black polyimide with high comprehensive performance for black flexible copper clad laminates

With the development of flexible printed circuit boards (FPCBs) and photoelectric devices, the demand for black polyimide (BPI) is increasing, but the existing BPIs have some problems, such as poor electrical properties, mechanical performance, masking ability and solubility. To solve these problems, a novel diamine monomer (TPCPOHPDA) containing tetraphenylcyclopentadienone (TPCP) grafted with hydroxyl groups and benzene rings was customized, and then TPCPOHPDA was polymerized with 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to obtain polyimide (TPCPOHPPI). TPCP had a broad UV–visible light absorption range (250–600 nm). Appending benzene rings and auxochrome (hydroxyl groups) on the TPCP skeleton extended the conjugated π-electron system and enhanced the mobility of electrons in the large π bonds, respectively. These structural modifications further extended its light absorption range, and the resulting TPCPOHPPI was dark black with a cutoff wavelength (λcut) of 680 nm and Commission International Eclairage (CIE) lab color parameter L* of 0.7. Simulation calculations indicated that the visible-light absorption that caused the black appearance of TPCPOHPPI was mainly due to the electron transition from HOMO to LUMO occurring within the TPCP-containing diamine moieties, in which the charge mainly transferred from the aryl moieties in positions 2 and 5 to the central cyclopentadienone core. Further investigation showed that TPCPOHPPI had excellent thermal, electrical and mechanical performances and high solubility. The TPCPOHPPI-based two-layer black flexible copper clad laminate (2L-FCCL) possessed good dip soldering resistance and peeling strength. This work provides a new idea for the design and synthesis of soluble intrinsic black polyimide with excellent comprehensive performance.

Numerical modelling of soldered superconducting REBCO stacks of tapes suggests strong reduction in cross-field demagnetization

Stacks of superconducting REBCO tapes (or “stacks”) can trap high magnetic fields, above 17 T. However, relatively low oscillating transverse magnetic fields can fully demagnetize the stacks. This is an issue if the stacks act as poles in the rotor of a superconducting motor, for instance. Here, we study the drastic suppression of cross-field demagnetization in stacks by soldering the tapes at the ends using a normal conductor. In particular, we analyzed by numerical modeling a stack of five REBCO thin films connected at the ends by resistances. The computed trapped field of a stack with zero solder resistance decays very fast at the beginning but then tends to stabilize to relatively high values, while the trapped field of an isolated stack (infinite resistance at the ends) decays further (it decays to zero if the transverse field is above the parallel penetration field). For intermediate solder resistances, the stable value of the trapped magnetic field is in between those of the isolated and zero-resistance configurations. Since the stable trapped field in soldered stacks increases with the number of tapes, stacks of sufficiently high number of soldered tapes could be immune to cross-field demagnetization. This opens the gate for a new kind of superconductors that mostly behave as bulks, especially if the stacks are made of delaminated tapes or it is possible to solder the tapes by very low resistance.

Effect of Ni-MOF Derivatives on the Electrochemical Corrosion Behavior of Sn-0.7Cu Solders

The corrosion resistance of solder joints is a critical factor affecting the service life of electronic products during long-term operation. In this study, the corrosion behavior of Sn-0.7Cu-xNi@C (x = 0, 0.04, 0.08, and 0.12 wt.%) composite solders was investigated using a Tafel polarization curve in 3.5 wt.% NaCl solution, and the result demonstrated that it was the Ni@C that enhanced the corrosion resistance of the composite solder. The corrosion rate of the composite solders decreased with increasing Ni@C content and reached the lowest value of 0.205 mm/y when the content of Ni@C reached 0.08 wt.%. Ni@C changed the morphologies of corrosion products Sn3O(OH)2Cl2 from thick flakes to dense fine needles and flakes, which made it more difficult for Cl– to break down corrosion products. Thus, the corrosion resistance of composite solder was improved. The carbon skeleton in Ni@C served as an inert physical barrier to inhibit further corrosion. Furthermore, the potential difference between IMC and β-Sn decreased with the addition of Ni@C, which reduced the corrosion rate of the electric couple and enhanced the corrosion resistance of the composite solder.

Enhancement mechanism of Te doping on microstructure, wettability and mechanical properties of Sn–Bi-based solder

Sn–Bi-based solder alloys have sparked tremendous research interest towards the development of low-temperature interconnecting materials in multi-level packaging interconnections electronic devices. Nevertheless, the research speed of solder is elusive to match well with the rapid development of integrated circuit design and manufacturing, which leads to the slow renewal course of electronic products. In the pursue for more effective modification strategies, Te was selected to be doped into Sn58Bi–1Sb (SBS) solder. As expected by the design, Te existed in the solder matrix in the form of solid solution and intermetallic compound simultaneously. To our satisfaction, Te enormously improved both the tensile strength and plasticity of the SBS solder. This largely circumvents the negative correlation between strength and plasticity during the modification process. Additionally, Te element significantly optimized the thermal properties, wettability, and creep resistance of SBS solder. Many tiny Bi particles embedded in Sn phase and strengthened the SBST solder matrix as the second phase. More strikingly, numerous Bi twin crystal structures were observed in the Sn58Bi–1Sb1Te (SBST) solder matrix, which occurred in Sn–Bi-based solder matrixes first time. The Bi phase twin represents preferable deformation ability of Bi phase and the plasticity of the solder matrix. It indicated that the doping of Te comprehensively enhanced the performance of SBS solder and may opened new horizons to the design route of alloying modification for Sn–Bi-based solder.

A closed-loop high temperature superconducting magnet energized by flux pump and its piecewise semi-analytical solution

High temperature superconducting (HTS) magnets energized by flux pumps can carry heavy current without heat leakage from current leads and are therefore appropriate for a wide range of applications. However, the soldering resistance remains an obstacle to the persistent operations of the HTS magnets. Here, we propose a closed-loop HTS magnet magnetized by flux pump with thermal switches. The magnet consists of a closed-loop single pancakes (SPs) coil wound by a rare-earth barium copper oxide (REBCO) tape on which a slit is cut to form a closed-loop ring within which current can flow without encountering the soldering resistance. Another REBCO tape is soldered on the closed-loop ring to form a pump bridge and a flux pump consists of a copper coil with iron core is installed around the pump bridge. There exists a group of manganese copper wires wound on the closed-loop ring and the pump bridge respectively as thermal switches. A piecewise semi-analytical solution is suggested to investigate the charging process by which the transport current in the magnet is calculated. Experiments are carried out to verify the feasibility of the magnet and the solution. The results show that the magnet can be operated in a persistent current mode, and thus, this study represents a practical solution for persistent operation of the HTS magnets. Besides, the proposed solution can effectively explain and predict the saturation current of the suggested magnet, which can, therefore, guide the design of other forms of HTS magnets and flux pumps.

Studies on Epoxy Resin Modified with Organic Agents

Epoxy composites are one of the most versatile thermosetting polymers widely used due to their strong soldering resistance, high insulation, and thermal resistance. A wide range of raw materials can be used for the preparation of epoxy resins, thus offering a variety of resins with highly controllable performance characteristics. Essentially, epoxy resins are low molecular weight liquids with two or more epoxide functional groups. To get superior properties of the composite material, a broad variety of inorganic and organic modification agents are used. For this study, two protein substances, gelatin, and wheat gluten were used to change the basic properties of three types of epoxy resins. The specific heat of modified epoxy resin materials was performed by using Differential Scanning Calorimetry (DSC) instrument. The thermal analysis was developed on two heatingcooling cycles and the specific heat was evaluated for each segment of the cycle analysis. Also, the mechanical behavior of organic modified polymers subjected to compression was studied using INSTRON compressive testing machine.

Study on Effects of Nonlinear Behavior Characteristics of Prepreg Dielectric on Warpage of Substrate under Laminating Process.

To analyze the effects of nonlinear behavior characteristics of prepreg (PPG) among the insulating materials of substrate and the residual stress of laminating process on the warpage of substrate, this study investigated the continuous laminating process using the numerical analysis by finite element method. The analysis results showed that the warpage of the substrate in the laminating process of PPG was very low, but it increased rapidly in the solder resist (SR) laminating process. As the laminating process of PPG continued, the stress inside the substrate increased continuously and it was predicted to decrease in the SR laminating process. These results confirmed that the warpage of the substrate is influenced the most by the SR laminating process, and that the warpage and stress of substrate accumulated in the laminating process of PPG have significant effects on the final warpage.

Thermomechanical fatigue resistance of low temperature solder for multiwire interconnects in photovoltaic modules

Novel interconnect technologies leveraging low melting temperature solders, such as multiwire interconnects, are being deployed in photovoltaic (PV) modules for improved reliability through interconnect redundancy and lower thermal loads during interconnection and lamination. However, the equivalency of standardized accelerated testing to field conditions has not yet been established for these emerging technologies. In this study, the thermomechanical fatigue resistance of low temperature solder alloys is investigated and compared to that of conventional SnPb to assess the acceleration behavior of these alloys. While InSn is shown to have sufficient thermomechanical fatigue resistance on the order of that of SnPb, these results indicate Sn–Bi alloys may have poor thermomechanical fatigue resistance at field conditions. The results also show that Sn–Bi alloys have thermal cycling acceleration factors of less than one. This indicates that the standardized accelerated thermal cycling test, such as that in IEC 61215, will produce misleading results for Sn–Bi alloys and that unique testing is required for this PV module architecture. Though accelerated thermal cycling may be a meaningful qualification test for SnPb solder joints, these results suggest that mechanical loading may be a more appropriate test for Sn–Bi multiwire interconnects. This is due to the distinct processing and geometry of multiwire interconnects which may allow for mechanical, rather than strictly metallurgical interconnections.

ИССЛЕДОВАНИЕ ЭРОЗИОННОЙ СТОЙКОСТИ ПАЯНЫХ СОЕДИНЕНИЙ С ЗАЩИТНЫМИ ПОКРЫТИЯМИ

Presents results of studies of the erosion resistance of soldered joints with various types of coatings. It was established that a coating based on tungsten carbide, applied by the electrospark method, has the greatest positive influence on the erosion resistance of VPr4 solder. At the same time, preliminary machining of the solder surface also increases resistance to the effects of erosion flow. The possibility of using an electrospark coating as an erosion-resistant sublayer for composite protective coatings was shown.

Two-Layer Solder Resist Film with Low Young’s Modulus for High Reliability

Abstract In this paper, we reveal the development of a novel two-layer Solder Resist (SR) film with low young’s modulus which consists of low young’s modulus layer that possesses excellent adhesion to substrate and thermal resistance layer which is composed of resins with high thermal resistance and great toughness. This novel two-layer SR film exhibits superior resolution and crack resistance. Furthermore, the amount of warpage is extremely low. In general, the material with low young’s modulus and high elongation is caused from weak cross-link density, resulting in poor thermal resistance and delamination which occurs when mounting at high temperature. Herein, we can inhibit delamination successfully by this new two-layer structure film with superior thermal resistance. The Coefficient of Thermal Expansion (CTE) of conventional SR for FC-BGA is 35 ppm, and modulus is 4.5 GPa, whereas, this advanced two-layer SR film exhibits CTE of 66 ppm, and modulus of 2.3 GPa. In order to compare the crack resistance between conventional SR and newly developed two-layer SR film, the film was laminated on BGA substrate (substrate size is 50 mm × 50 mm), patterned by photolithography and cured, and then, 25 mm × 25 mm chip was mounted on a BGA substrate by flip-chip bonder. Conducting thermal cycle test (TCT) and observing the number of cracks after 1000 cycles of TCT. The crack occurrence frequency of the conventional SR is 65 %, whereas that of the new two-layer SR film is 4 %. We proved clearly that high CTE and low young’s modulus demonstrate overwhelmingly high crack resistance. Besides, high resolution of this newly developed two-layer film enabled the formation of SR opening (SRO) as small as 40 μm. From the above results, the newly developed two-layer SR film with low young’s modulus is beneficial for the next generation high-density package, especially for the outermost layer of FC-BGA packages and interposers that require higher reliability.

Effect of Ni Content on the Microstructure Formation and Properties of Sn-0.7Cu-xNi Solder Alloys

Sn-Cu based solders have been widely investigated due to their good mechanical properties, good fluidity, narrow melting range, environmental friendliness, and low price. In this paper, the effect of Ni content on the microstructure, mechanical properties, melting behavior, spreadability, and conductivity of Sn-0.7 Cu-xNi (0.5-2.0 mass%, mass fraction except when specified) lead-free solders was studied. The Sn-0.7Cu-xNi (x = 0.5, 1.0, 1.5, and 2.0) solder alloys consisted of a β-Sn solid solution, Ni3Sn4 phase, and Cu6Sn5 phase. The volume fraction of Ni3Sn4 increased with increasing Ni content. The addition of Ni increased the solidus and liquidus temperatures of the Sn-0.7Cu-xNi solder alloys. However, the melting range of the Sn-0.7Cu-0.5Ni and Sn-0.7Cu-1.0Ni solder alloys is lower than that of the Sn-0.5Cu solder alloy. The spreading area of the Sn-0.7Cu-xNi solder alloy first increased and then decreased with increasing Ni content. Moreover, the ultimate tensile strength and hardness of the Sn-0.7Cu-xNi solder alloy increased gradually with increasing Ni content. The Sn-0.7Cu-2.0Ni alloy has maximum ultimate tensile strength and hardness values of 52.01 MPa and 16.45 Hv, respectively. However, the electrical conductivity of the Sn-0.7Cu-xNi solder alloy decreased with increasing Ni content. These changes in performance related to the formation of the intermetallic Ni3Sn4 phase. The Sn-0.7Cu-1.0Ni solder alloy had the best comprehensive performance in the present experiment. For the Sn-0.7Cu-1.0Ni solder alloy, the expanded area was 1.28 times that of the Sn-0.7Cu alloy, and the liquidus temperature, melting range, strength, hardness, and resistivity of the alloy solder were at the intermediate level among the Sn-0.7Cu-xNi solder alloys. Therefore, the Sn-0.7Cu-1.0Ni alloy is a relatively ideal solder alloy with a good comprehensive performance among the Sn-0.7Cu-xNi solder alloys.

Design of a Test Rig for the Characterization of Thermal Fatigue and Soldering Resistance of the Surfaces of Tool Steels for High‐Pressure Die‐Casting Dies

The conceptualization and development of a test rig able to reproduce thermal stresses and contact with molten aluminum alloy, typical of high‐pressure die‐casting dies, are described. During the test, a hot‐work tool steel sample is cyclically heated by contact with molten aluminum alloy (AlSi11Cu2(Fe)) and then cooled by the spraying of a water‐diluted silicone‐based lubricant. A finite element method (FEM) simulation is setup to determine the temperature at different depths beneath the sample surface during thermal cycling and is experimentally validated to design the proper sample geometry aimed at reproducing the stress/strain conditions experienced by a die‐casting die insert. A tensile–compressive stress state is achievable on the surface of the sample by machining a notch with a suitable radius, which is able to produce a plastic strain comparable with the insert one. A thermally induced stress–strain fatigue loop is determined for both the sample and the component. Temperatures are monitored discontinuously by infrared (IR) thermography after heating and continuously by thermocouples placed at a reference depth of 5.5 mm. Finally, the optimized testing conditions are validated experimentally: both thermal cracking and soldering phenomena are successfully reproduced on a lab‐scale test rig.

Influence of kaolin geopolymer ceramic additions to the wettability and electrical properties of Sn-3.0Ag-0.5Cu (SAC305) lead free solder

The effect of kaolin geopolymer ceramic addition to the wettability and electrical resistivity of Sn-3.0Ag-0.5Cu (SAC305) lead free solder was successfully explored. Powder metallurgy with microwave sintering method was used to fabricate SAC305 composite solder. Five different weight percentage (wt.%) of kaolin geopolymer ceramic (0, 0.5, 1.0, 1.5 and 2.0 wt.%) were used in this study. The wettability of composite solder revealed the optimum contact angle was achieved at 1.0 wt.% with 20.8 °. Then, the electrical resistivity of composite solder showed significant change in the resistivity value.

Characterization of geopolymer ceramic reinforced Sn-0.7Cu composite solder: Effect of milling time and speed.

The effect on the addition of optimally ball milled kaolin and fly ash geopolymer ceramic as reinforcement on the morphology and electrical properties of Sn-0.7Cu composite solder were explored. Geopolymer ceramics from fly ash class F and kaolin were prepared using geopolymer technology, milled at various speed and time. 1.0 wt. % of each sample were used to form composite solder via microwave sintered through powder metallurgy method. Structural characterization via SEM reveals that kaolin geopolymer ceramics has nano-sized subangular powder particles with larger amount of open porosity compared to fly ash geopolymer ceramics when milled at optimum speed and time. Four Point Probe test results showed a decreasing trend of electrical resistivity for kaolin geopolymer ceramics as the milling speeds and times increased. Overall, the results compared to electrical resistivity of other composite solder with various typical ceramic reinforcement additions, proves that kaolin geopolymer ceramics reinforcement to be the best option so far in term of morphology, electrical properties and its sustainable manufacturability.

Effect of surface finish on the wettability and electrical resistivity of Sn-3.0Ag-0.5Cu solder

The effect of different surface finish with Sn-3.0Ag-0.5Cu (SAC305) solder was successfully investigated. The SAC305 solder was fabricated by using casting method and solder was placed on copper substrate that coated with different surface finish. The soldering process was carried out by using F4N reflow oven followed up with the mounted and metallographic steps. Wettability of SAC305 solder was observed through contact angle formed between solder and four different surface finish located on the copper substrate. Subsequently, the electrical resistivity of solder was studied by conducted the four-point probes. The results of wettability test was found to be in the accepted range which is below 45° for all different surface finish. In terms of electrical resistivity, the results showed that the ImAg surface finish had enhanced the electrical conductivity of SAC305 lead-free solder.