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Head-in-pillow (HiP) is a BGA defect which happens when solder balls and paste can’t contact well during reflow soldering. Package warpage was one of the major reasons for HiP formation. In this paper, package warpage was measured and simulated. It was found that the package warpage was sensitive to the thickness of inside chips. A FEM method consi...
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... As the demand and interest in flexible and wearable devices/substrates increases and the miniaturization and integration trend of microelectronics devices increases, interest and research on materials and processes of the low melting temperature bonding are significantly increasing [1][2][3][4][5]. Under this background, the laser soldering processes are attracting attention owing to its advantages of non-contact heating, localized heating, and fast bonding compared to the conventional reflow soldering process [6][7][8][9][10][11]. Especially, the laser soldering technology can significantly reduce the thermal damage of the devices, active/passive J Mater Sci: Mater Electron (2023) 34:1960 1960 Page 2 of 15 OSP joints exhibited superior properties compared to the Sn-58Bi/electroless nickel-electroless palladium-immersion gold (ENEPIG) and Sn-58Bi/electroless palladium-immersion gold (ENIG) joints [21]. ...
... (wt%) have been mainly conducted. Recently, researches on low-melting temperature solders have been increased to reduce thermal budget and device damage due to excessive heat application, warpage, and coefficient of thermal expansion (CTE) mismatch between the solder materials and the substrate [1,2,[15][16][17]. In addition, low-melting temperature solder is essential for flexible and wearable devices/substrates that need to minimize damage. ...
In this study, the bonding reliability and characteristics of laser soldering and reflow soldering using a low-melting temperature Sn–58Bi solder/organic solderability preservative finished Cu joints were compared and analyzed. Because laser soldering uses high density energy, it enables faster and more localized soldering compared to conventional reflow soldering. As a result of laser soldering, thin and small intermetallic compounds (IMCs) were formed under the condition of applying lower energy, but thick and large IMCs were formed under the condition of applying higher energy. As the bonding time increased at the same laser power, a relatively thick and long Cu6Sn5 was formed at the interface. To evaluate long-term reliability, a high temperature storage test (HTST) was performed at 110 °C, and Cu3Sn IMC formation was observed at the interface after HTST for 100 h under all laser soldering conditions. After 2000 h of HTST, the shear strength tended to decrease and the thickness of the interfacial IMC tended to increase. Initially, ductile fracture occurred, and the brittle fracture proportion increased as the HTST time increased. The joints formed under the laser soldering condition showed relatively higher shear strength even after long-term heat treatment compared to the reflow soldering joints. From these results, it was confirmed that the laser soldering process is superior in terms of long-term reliability of Sn–58Bi/Cu joint compared to the reflow soldering process.
... It helps to avoid connection failure following re-design of a product. Moreover, in the case of a relatively larger component with more soldered connections (e.g., ball grid array) that undergoes warpage itself due to the fact of CTE mismatch of the component, mechanically weak solder joints (called head-in-pillow) may occur [15]. Tearing off of the soldering pad from the substrate may appear during soldering while the joint has already solidified and warping of the assembly is still ongoing or at field conditions when CTE differences in the substrate and mounted components raise the stress concentration [16,17]. ...
The purpose of this study was to compare the strength of the bond between resin and glass cloth for various composites (laminates) and its dependence on utilized soldering pad surface finishes. Moreover, the impact of surface finish application on the thermomechanical properties of the composites was evaluated. Three different laminates with various thermal endurances were included in the study. Soldering pads were covered with OSP and HASL surface finishes. The strength of the cohesion of the resin upper layer was examined utilizing a newly established method designed for pulling tests. Experiments studying the bond strength were performed at a selection of laminate temperatures. Changes in thermomechanical behavior were observed by thermomechanical and dynamic mechanical analyses. The results confirmed the influence of the type of laminate and used surface finish on bond strength. In particular, permanent polymer degradation caused by thermal shock during HASL application was observed in the least thermally resistant laminate. A response to thermal shock was detected in thermomechanical properties of other laminates as well, but it does not seem to be permanent.
... Industry practitioners have explored the various potential contributing factors for BGA defects such as package warpage [5,6], PCB and stencil printing parameters [7,8], and solder paste or solder alloy composition [6,9,10]. ...
... The second type of articles considered was those discussing BGA defects in any manner whatsoever. Of the 20 articles in this group, eight focused on x-ray or other optical technology to detect existing defects [12][13][14][15][16][17][18][19], four explored the metallurgical properties of the solder [6,10,20,21], three involved somewhat specific subsets of the BGA package type [22][23][24], three involved rework of BGA defects [4,5,25], and two focused on the stencil-printing process [8,26]. ...
... Lee et al. (2017) Temporal and frequency characteristic analysis of margin-related failures caused by intermittent nanoscale fracture of the solder ball in a BGA package device[23] Specific subset of BGA package typeLee and Park (2015) Prediction enhancement of the J-lead interconnection reliability of land grid array sockets[24] Specific subset of BGA package type Wetterman (2017) Top 5 BGA challenges to overcome[4] BGA defect reworkZhao et al. (2015) Effects of package warpage on head-in-pillow defect[5] BGA defect reworkChen et al. (2014) ...
This research presents an exploratory data analytics case study in defect prediction on printed circuit boards (PCB) employing ball grid array (BGA) package types during assembly. BGA package types are of interest because defects are difficult to identify and costly to rework. While much of the existing research is dedicated to techniques to identify and diagnose BGA defects, this research attempts to preempt them by using parametric data measured by solder paste inspection (SPI) machines as input data to applied machine learning models. Two modeling approaches are explored: one approach to analyze individual solder paste deposits and the other approach to holistically analyze all solder paste deposits on a single PCB location. The latter approach employs feature generation to extract a broad set of features from the arrays of SPI data and feature selection techniques for dimensionality reduction. Models trained on the reduced feature sets provide encouraging initial results, with precision, recall, and f1 score metrics exceeding 0.82, 0.50, and 0.62 respectively for each of two datasets analyzed.
... The case study that undergirds this research utilizes an applied machine learning model to link SPI parametric data with downline ICT defects. This case study is innovative in the landscape of surface mount technology literature, as the bulk of current research into BGA defects focuses on optical means to locate them ( [5]- [12]), metallurgical properties of the solder ( [13]- [16]), or rework ( [17]- [19]). Employing parametric data measured on the individual solder paste deposits is an approach that is only possible in the Connected Enterprise Environment and is enabled by a circa-2017 Industrial Internet of Things (IIOT) capability enhancement project at the manufacturing facility from which the data is obtained. ...
Industry 4.0 capabilities have enabled manufacturers to collect and analyze smart manufacturing data across a broad array of diverse domains including but not limited to scheduling, production, maintenance, process, and quality. This development necessarily proceeds in a logical sequence by which first the organization develops the capability to capture and store this data and, at best concurrently but frequently lagging, develops and refines the competencies to analyze and effectively utilize it. This research presents an applied case study in surface mount technology (SMT) manufacture of printed circuit board (PCB) assemblies. Parametric data captured at the solder paste inspection (SPI) station is analyzed with machine learning models to identify patterns and relationships that can be harnessed to preempt electrical defects at downline inspection stations. This project is enabled by the recent conclusion of an Industrial Internet of Things (IIoT) capability enhancement at the manufacturing facility from which the data is drawn and is the logical next step in achieving value from the newly-available smart manufacturing data. The operationalization of this analysis is contextualized within the product-resource-order-staff architecture (PROSA) of a Holonic Manufacturing Systems (HMS). A Trigger Holon is nested between the Resource Holarchy and Product Holarchy that, at scheduling, distributes implementation instructions for the defect-prediction model. The Defect Prediction Holon is containerized within the Product Holarchy and provides instructions for corrective action when the model flags a record as exhibiting increased probability of a downline electrical defect.
... It can be expected that the growth of the interfacial IMC formed between the undercooled liquid solder and the metallization pad should be slow due to the lower soldering temperature than the normally used soldering temperature, which is generally several tens degrees Celsius higher than the melting point of the solder. Some studies have shown that with decreasing the dimensions of solder joints, the degree of undercooling of the solder increases significantly during solidification [23][24][25], the solder joint can maintain liquid state stably at low temperature during the undercooling soldering process, which can also significantly reduce the thermal stress of the electronic components during the soldering process for obtaining good metallurgical bonding [26][27][28]. Therefore, it is highly interesting and meaningful to perform a systematic study of the interfacial reaction between the undercooled liquid lead-free solder and the Cu metallization (pad), and the growth behavior of interfacial IMC, as well as the mechanical performance and fracture behavior of the solder joints formed during the low temperature soldering process. ...
A novel technique is proposed to prepare Sn–3.0Ag–0.5Cu/Cu joints at three different processing temperatures, which are called undercooled liquid (UL, 213.0 °C), eutectic liquid (EL, 217.0 °C) and normal liquid (NL, 231.0 °C) soldering temperatures correspondingly, and each of them is lower than, equal to and higher than Sn–3.0Ag–0.5Cu solder’s melting point (217.0 °C), respectively. The interfacial reaction, intermetallic compound growth and mechanical performance of Sn–3.0Ag–0.5Cu/Cu joints formed during UL, EL and NL soldering processes were investigated systematically. Results show that for Sn–3.0Ag–0.5Cu solder as the undercooled liquid melt or eutectic liquid melt or normal liquid melt in the formation of joints, the thickness of interfacial intermetallic compound (IMC) layer in the joints increases with prolonging dwelling time. For three different liquid soldering processes, the change tendency of the interfacial IMC layer thickness is distinct. For joints formed at UL and EL temperatures, the excessive growth of primary Cu6Sn5 and interfacial IMC (mainly Cu6Sn5) can be suppressed during isothermally dwelling in the liquid state for more than 5 min. Ball shear test results show that solder joints formed at UL and EL temperatures have lower value of the maximum shear force (MSF) than those formed during the NL soldering process. For UL and EL types of joints, the fracture occurs either by shear slide fracture totally along the shear tool tip movement plane (i.e., in-plane shear slide fracture) or by shear slide fracture initially along the shear tool tip movement plane and afterwards shear deformation fracture in the solder matrix under the plane (i.e., out-of-plane shear slide and deformation mixed-mode fracture), while the fracture takes place in NL joints only by in-plane shear slide fracture mode.
... The higher reflow soldering temperature required for Sn-Ag-Cu solder would result in thermal warpage on these components and the board. • Reliability issue under the higher soldering temperature, the solder joint quality was easily deteriorated with the formation of Head-on-Pillow (HoP) due to the warpage of components [7]. • Economic issue it is related with energy costs from running the reflow soldering system and material costs from the Ag-contained solders. ...
With the implementation of legislations on inhibiting the usage of Sn–Pb solder in consumer electronic products, Sn–Ag–Cu series solder has been gotten the most application. However, there are some stimulations from electronic manufacturers to adopt low temperature soldering such as the economic driver from the reduction in manufacturing assembly cost and the reliability driver to avoid the dynamic warpage of area array components caused from Sn–Ag–Cu solder. Sn–Bi series solder is one of the promising candidates, which met the requirements for low melting point, low cost and environment friendly. However, the disadvantage of brittleness characteristic prevented its wide practical application. In order to promote the better application of Sn–Bi based solders, many efforts have been made to improve the wettability, mechanical properties and reliability of Sn–Bi based solders. This paper will summarize the related results about Sn–Bi solder alloys from wettability, interfacial reaction, mechanical properties of Sn–Bi solder and reliabilities of Sn–Bi solder joints. Moreover, in order to improve the properties of Sn–Bi solders, researchers have done lots of works on effect of addition of element dopants. The corresponding works of effect of alloying elements on the properties of Sn–Bi solder were also focused. According to the existing research results, it provides an important basis of understanding the current development of Sn–Bi solders.
... As the interconnected material, Sn-Ag-Cu series Pb-free solder alloy attracts the most application in the assembly process to replace traditional Sn-Pb solder due to the increasing awareness on environmental protection in the past decade [1,2]. However, Sn-Ag-Cu solder has a higher melting temperature than Sn-Pb solder, and inevitably exerts a higher thermal load on the packaging components, which possibly induces the thermal warpage on them with the continual miniaturization and densification of electronic devices [3,4]. Therefore, as another promising Pb-free solder, Sn-58Bi recently gets much attention because it provides a low temperature soldering process due to its lower melting temperature at 138 °C, acceptable wettability, good tensile strength and creep resistance [5][6][7][8]. ...
Sn–58Bi solder recently attracts much attention for low temperature soldering, but is also restricted by the degradation on Sn–Bi solder joint from the interfacial Bi embrittlement. This study introduced a thin solder layer with the composition of Sn–3.0Ag–0.5Cu (SAC) on Cu pad to improve the interfacial structure and shear properties of Sn–58Bi solder joints under soldering and the subsequent aging conditions. SAC solder layer with the thickness about 5 μm was coated on Cu pad using Hot Air Soldering Leveling (HASL). During soldering condition, the thickness of interfacial intermetallic compound (IMC) layer in Sn–58Bi joints increased with the soldering times, and there was no obvious difference on the bare and SAC-coated Cu. However, during aging condition, the growth on interfacial IMC layer was effectively retarded by the SAC coating compared to their bare Cu counterparts. SAC-coated samples that were reflowed with varying soldering times and then aged also showed a thinner IMC layer. The retarding effect on IMC growth from SAC-coated Cu pad was attributed to the reason that SAC solder on Cu produced an initial Cu6Sn5 layer with fewer scallops, fewer grain boundaries between scallops, and therefore fewer diffusion pathways for Cu atoms to diffuse into the solder and react to grow the intermetallic layer. Ball shear tests also showed that aged SAC-coated joints displayed higher shear strength and through-solder ductile failure while Sn–58Bi on bare Cu pad displayed lower shear strength and brittle failure through the interfacial IMC layer. Therefore, SAC Pb-free solder can be recommended as the surface finishing on Cu pad to improve the performance of Sn–58Bi joints because it can be easily realized by HASL method in electronic industry.
Warpage occurring during surface-mount assembly reflow processes may lead to severe solder bump reliability problems. In this research, a finite-element simulation analysis of the effect of warpage on SAC305 solder joint fatigue life in a plastic ball grid array (PBGA) package was carried out. Due to the warpage of the PBGA package, the heights and solidified shapes of solder joints located at different positions are different. First, a finite element model was established to obtain the warpage, and experimental measurements were conducted to verify the accuracy of the model. The shapes of all solder joints affected by warpage were obtained through Surface Evolver software. Finally, a solder joint fatigue life prediction model, combining package warpage and solder joint shape, was established through finite element analysis. A model without considering warpage, which was assembled with uniformly height solder joints, was also established to calculate the fatigue life of solder joints under the same conditions. The effect of warpage on solder joint fatigue life can be revealed by comparing the results of the two models. The results show that taller solder joints have a longer fatigue life. Warpage changes the location of solder joints most susceptible to fatigue failure from the bottom near the corners of the package to the bottom near the corners of the die. Due to the existence of warpage, the fatigue life of critical solder joints is, on average, 20% less than the predicted result of the model without warpage.
The demand for flexible wearable devices/substrates with miniaturization and improved integration in microelectronic devices has intensified the research interest in low-temperature laser soldering processes as an alternative to conventional reflow soldering processes owing to their advantages, such as local heating, non-contact heating, and short bonding time. In this study, we compared and evaluated the reliability of laser soldered and conventional reflow soldered joints using representative low melting temperature eutectic SnBi solder and thin electroless Ni-electroless Pd-immersion Au (ENEPIG)-finished Cu pads. Laser soldering was performed using various laser powers (130, 150, and 170 W) and times (2 and 4 s). Furthermore, an aging test was performed at 110 °C for 2000 h to evaluate the long-term reliability of the soldered joints. The mechanical properties, including the top and cross-sectional views and fracture surfaces, of the soldered joints were analyzed by conducting shear tests after aging. During laser soldering, various intermetallic compounds (IMCs) were formed at the joints depending on the applied energy. The metallization layer and Cu reacted with Sn in the solder after different aging durations, and additional IMCs were formed and grown. After aging for 2000 h, the shear strength decreased, and the interfacial IMC thickness increased. As the aging time increased, the fracture mode changed from an initial ductile fracture to brittle fracture (between the solder and IMCs and/or between IMCs and the Cu pad). The reflow soldered joints exhibited stable shear strength, resulting in ductile fracture until aging for 500 h. However, the shear strength decreased sharply after aging for 1000 and 2000 h, and Bi-segregation was observed after aging for 1000 h, resulting in inferior long-term reliability. After laser soldering at 150 and 170 W for 4 s, the strength of the samples decreased sharply after aging for 1000 and 250 h, respectively, and Bi-segregation was observed after aging for 2000 h. The shear strength of the sample laser soldered at 170 W for 2 s gradually decreased with increasing aging time and maintained a stable shear strength until aging for 2000 h. Therefore, laser soldering at 170 W for 2 s was considered as the optimal condition for long-term reliability.
