Janusz Sitek, Marek Koscielski, Janusz Borecki and Tomasz Serzysko
The purpose of this paper is to evaluate the influence of solder powders sizes applied in soldering materials used for Package-on-Package (PoP) system manufacture as well as other…
Abstract
Purpose
The purpose of this paper is to evaluate the influence of solder powders sizes applied in soldering materials used for Package-on-Package (PoP) system manufacture as well as other factors on reliability and mechanical strength of created solder joints in three-dimensional (3D) PoP structures.
Design/methodology/approach
The design of experiments based on the Genichi Taguchi method were used in the investigation. The main factors covered different printed circuit board (PCB) coatings, soldering materials with solder powders sizes from Types 3 to 7 and soldering profiles. The reliability of 3D PoP structures was determined by measurements of resistance of daisy-chain solder joints systems during thermal shocks (TS) cycles. The mechanical strength of solder joints in 3D PoP structures was determined by measurements of a shear force of “Top” layer of 3D structures at T0 and after 1,500 TS. The ANOVA was used for results assessment.
Findings
The size of solder powders applied in soldering materials had small (10 per cent) influence on mechanical strength of solder joints in 3D PoP structures. Small size of solder powder had positive effect on solder joints reliability in 3D PoP structures. Especially important was the selection of solder paste for “Bottom” layer of 3D PoP system (influence 17 per cent). Incorrect soldering profile (influence 46 per cent) or wrong selected PCB coating (influence 35 per cent) can very easily reduce the positive impact of soldering materials on solder joints reliability. It was stated that as low as possible soldering profile and organic solderability preservative (OSP) coating in the case of single-sided PCB are the best for 3D PoP structures due to their reliability.
Originality/value
This paper explains how different sizes of solder powders used nowadays in solder pastes influence on reliability and mechanical strength of the solder joints in 3D PoP structures. The contribution, in numerical values, of soldering materials, soldering profile and PCB coating on 3D PoP structures solder joints reliability as well as recommendations improving reliability of 3D PoP structures solder joints were presented.
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Yan Zhang, Janusz Sitek, Jing-yu Fan, Shiwei Ma, Marek Koscielski, Lilei Ye and Johan Liu
Multiple fillers are adopted to study the filler influences on electrical and mechanical properties of the conductive adhesives. The performances of the developed nano-enhanced…
Abstract
Purpose
Multiple fillers are adopted to study the filler influences on electrical and mechanical properties of the conductive adhesives. The performances of the developed nano-enhanced interconnect materials in printing process are also evaluated. The paper aims to discuss these issues.
Design/methodology/approach
Micron-sized silver flakes are used as the basic fillers, and submicro- and nano-sized silver spheres and carbon nanotubes (CNTs) are adopted to obtain conductive adhesives with multiple fillers. Differential scanning calorimetry measurement is carried out to characterize the curing behavior of the samples with different fillers, four-probe method is used to obtain the bulk resistivity, shear test is conducted for adhesive strength, and environmental loading test is also involved. Furthermore, printing trials with different patterns have been carried out.
Findings
The electrical resistivity of the adhesives with submicro-sized silver spheres does not monotonically change with the increasing sphere proportion, and there exists an optimized value for the ratio of silver flakes to spheres. Samples with relatively small amount of CNT additives show improved electrical properties, while their mechanical strengths tend to decrease. For the printing application, the adhesives with 18.3 volume% filler content behave much better than those with lower filler content of 6 percent. The presence of the nano-particles makes a slight improvement in the printing results.
Research limitations/implications
More detailed printing performance and reliability test of the samples need to be carried out in the future.
Originality/value
The conductive adhesives as interconnect materials exhibit some improved properties with optimized bimodal or trimodal fillers. The additive of the nano-fillers affects slightly on the printing quality of the bimodal conductive adhesives.
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Janusz Sitek and Marek Koscielski
The purpose of this paper is to investigate the influence of different micro additives to new compositions of electrically conductive adhesives (ECA) on their printing properties…
Abstract
Purpose
The purpose of this paper is to investigate the influence of different micro additives to new compositions of electrically conductive adhesives (ECA) on their printing properties as well as electric parameters expressed in resistivity of joints cured in low temperatures and obtain recommendations for elaboration of ECA appropriate for printing electronic applications.
Design/methodology/approach
The three different types of silver flakes and two types of micro powders were added to basic matrix of ECA to create ECA composition for investigation. The ECA were printed via stencil on elastic substrate creating the special designed samples which next were cured in 25°C, 50°C or 80°C. The SEM with EDS analysis was utilized for assessment of shapes and sizes of the input materials for ECA. The microscopic observation and resistivity measurements of samples by four-probe method were used for assessment of the influence of ECA compositions on prints quality as well as on electric parameters of adhesives joints.
Findings
The results show that the quality of the prints made with the use of elaborated adhesive compositions is related mainly with the amount and type of filler used in ECA. The electrical properties of joints were dependent from type of silver flakes and amount of micro-additives as well as curing temperature.
Research limitations/implications
It is suggested that further studies are necessary for the confirmation of the practical application, especially of the mechanical and reliability properties of the joints obtained with the use of final composition of the elaborated ECA.
Originality/value
The presented results of analyses provide information regarding the correlation between the composition of ECA, properties of elements creating them and the results of printing and electric parameters of joints produced of them. It showed positive impact of small carbon micro powder addition both on printing results and resistivity of joints. It pointed out also that the purity of silver components of ECA influences significantly on resistivity of ECA's joints. It is valuable information for ECA's designers as well as end-users, from the practical point of view.
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Krystyna Bukat, Janusz Sitek, Marek Koscielski, Zbigniew Moser, Wladyslaw Gasior and Janusz Pstrus
The purpose of this article is to establish why the wetting on PCBs with SnCu (HASL) and Snimm finishes in the presence of a flux is better than the wetting of those on a copper…
Abstract
Purpose
The purpose of this article is to establish why the wetting on PCBs with SnCu (HASL) and Snimm finishes in the presence of a flux is better than the wetting of those on a copper substrate. The practical aspect of the obtained results is the main goal of these investigations.
Design/methodology/approach
The authors applied the wetting balance method for the wetting measurements at 230 and 250°C, in nitrogen atmosphere, in the presence of the ORM0 type flux. The PCBs with the SnCu (HASL) and Snimm finishes were investigated in the state “as received”. To establish the wetting properties of the SnCu (HASL) and Snimm finishes on the PCBs, wetted by the investigated SnZnBiIn alloys, the SEM and EDX analyses were performed.
Findings
The authors obtained very good wetting results of the PCBs with the SnCu and Snimm finishes, wetted by the SnZn7Bi3In4 alloys. By applying the SEM and EDX methods, it was possible to establish that the barrier layer which was created during the HASL process between the copper and the SnCu solder is efficient enough to protect the copper against the influence of the Zn atoms from the SnZn7Bi3In4 solder. This is the reason for an improvement of the wetting properties. An immersion tin finish does not create such barrier layer with the copper. It results in a worse wetting than for the SnCu finishes but a better one than that for the copper. Immersion tin dissolves in the alloys during the soldering and this process delays the reaction between the copper and the Zn atoms from the SnZn7Bi3In4 solder.
Research limitations/implications
It is suggested that further studies are necessary for the confirmation of the practical application, but they should be limited to the reliability of the solder joint performance.
Practical implications
The best wetting results of the PCBs with “tin finishes”, especially with SnCu, wetted by the SnZn7Bi3In4 alloy, at 230 and 250°C and in nitrogen atmosphere, suggest a possibility of a practical usage of the tin‐zinc‐bismuth‐indium alloys for soldering in electronics.
Originality/value
The wetting balance method combined with the SEM and EDX analyses were used as the quickest way to determine the mechanism of the better wettability properties in the case of the PCBs with the SnCu and Snimm finishes, wetted by the SnZn7Bi3In4 alloy, compared to those of the PCBs on the Cu substrate.
Przemyslaw Fima, Tomasz Gancarz, Janusz Pstrus, Krystyna Bukat and Janusz Sitek
The purpose of this paper is to study the effect of copper concentration in near‐eutectic liquid SAC solders on their thermophysical properties: viscosity, surface tension…
Abstract
Purpose
The purpose of this paper is to study the effect of copper concentration in near‐eutectic liquid SAC solders on their thermophysical properties: viscosity, surface tension, density; as well as wetting behavior on copper substrates at 523 K.
Design/methodology/approach
Viscosity, surface tension, and density were studied over a broad range of temperatures with the recently developed Roach‐Henein method. The obtained results were compared with the data from modified capillary, maximum bubble pressure, wetting balance and dilatometric measurements. Wetting angles measured with wetting balance method were compared with the results of sessile drop measurements.
Findings
The results obtained indicate that increasing concentration of copper in the alloy results in higher density, surface tension and viscosity, but differences resulting from copper concentration on wettability are relatively small. At 523 K, the density is: 7.097, 7.186, 7.232 g cm−3, the surface tension is: 538.1, 553.5, 556.7 m Nm−1, the viscosity is: 2.173, 2.227, 2.467 mPas, respectively, for alloys containing 0.41, 1.01 and 1.61 wt% of Cu. Wetting angles on copper substrates are similar within a margin of error for all compositions. The results of present study are compared with the available literature data and a relatively good agreement is observed.
Originality/value
This paper provides the data of thermophysical properties of widely‐used SAC solders including viscosity, of which there is little data in the literature. It is confirmed that the increased copper concentration increases viscosity, yet this effect is small and does not correlate with the wetting behavior.
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Marek Koscielski and Janusz Sitek
The purpose of this paper is to investigate the influence of the properties of new compositions of fluxes for selective soldering on lead-free solder joints quality and…
Abstract
Purpose
The purpose of this paper is to investigate the influence of the properties of new compositions of fluxes for selective soldering on lead-free solder joints quality and microstructures as well as showing which flux properties are the most important.
Design/methodology/approach
The three different types of fluxes were tested, which differed in composition, solids content, amount and type of activators added. The selective soldering process was done with the use of lead-free solder SAC 305. The test boards had two coatings SnCu (HASL) or Au/Ni. Basic chemical and physical properties of fluxes were examined according to the relevant standards. Different types of components from the bulky ones, demanding more heat, to the smaller ones were used during the assembly process. AOI and X-ray analyses as well as cross-sections and SEM analyses were utilized to deeply assess the quality and microstructure of the investigated solder joints.
Findings
The results showed that information about density or static activity of flux is not enough for correct flux assessment. The dynamic activity of flux measured by wetting balance method is the best for this, especially in the case when there is short soldering time and heat transfer is hindered. The quality and the microstructure of lead-free solder joints are related not only with wetting properties of the flux used for soldering but also with other properties like solids content in a flux.
Research limitations/implications
It is suggested that further studies are necessary for the confirmation of the practical application, especially of the reliability properties of the joints obtained with the use of the elaborated fluxes.
Originality/value
The results showed that type of flux (ORL or ROL) as well as minor changes in their dynamic activity and solids content might have significant influence on quality of solder joints and their microstructure. It was noted that selective soldering is demanding technique and optimization of soldering process for different type of components and fluxes is important.
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Janusz Sitek, Dubravka Ročak, Krystyna Bukat, Janeta Fajfar‐Plut and Darko Belavič
The European Commission has decided that from the second half of 2006 only lead‐free solder pastes will be permitted for use in the electronics industry. Earlier results of…
Abstract
The European Commission has decided that from the second half of 2006 only lead‐free solder pastes will be permitted for use in the electronics industry. Earlier results of testing showed that lead‐free solder pastes may not be appropriate for both printed‐circuit‐board (PCB) and hybrid‐circuit applications, because of the materials' compatibility with the soldering process and with the solder pads. The basic properties of the investigated pastes show which of the tested solder pastes can be used for both applications. After selection of the appropriate solder pastes, reliability tests were conducted. The surface insulation resistance was tested for both the hybrid circuits and PCBs, whereas the mechanical strength of the soldered joints of components was only tested for the PCBs.
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Marek Kościelski, Janusz Sitek, Wojciech Stęplewski, Grazyna Kozioł, Piotr Ciszewski and Tomasz Krzaczek
– The purpose of this paper is to present challenges met during package-on-package (PoP) technology implementation in real surface-mount technology assembly processes.
Abstract
Purpose
The purpose of this paper is to present challenges met during package-on-package (PoP) technology implementation in real surface-mount technology assembly processes.
Design/methodology/approach
The properties and behavior of different combinations of soldering materials, PoP components and soldering profiles were investigated, both in the laboratory and during production trials. The purpose of such an approach was identification of existing problems and challenges in lead-free PoP systems assembly as well as checking which soldering material designed to PoP is more suitable for this technology.
Findings
Technological trials are needed to select adequate soldering materials for PoP systems assembly, as laboratory tests of materials alone were not sufficient. The challenges of PoP technology were associated with the equipment utilized, the soldering materials, operational parameters and the soldering profile used for assembly. The localization of defects in PoP systems is very difficult and, in many cases, destructive methods have to be used on solder joints for the assessment and confirmation of failures.
Originality/value
This paper shows main materials and soldering challenges in lead-free PoP technology. In particular, the problem related with selection of soldering materials and soldering profiles for PoP was presented. Moreover, the issues that have to be taken into consideration during the planning of a PoP system assembly procedure are presented.
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Janusz Sitek, Wojciech Stęplewski, Kamil Janeczek, Marek Kościelski, Krzysztof Lipiec, Piotr Ciszewski and Tomasz Krzaczek
The purpose of this paper is to evaluate the influence of assembly parameters on lead-free solder joints reliability in Package-on-Package (PoP) Technology and demonstrate factors…
Abstract
Purpose
The purpose of this paper is to evaluate the influence of assembly parameters on lead-free solder joints reliability in Package-on-Package (PoP) Technology and demonstrate factors important for this issue.
Design/methodology/approach
Two types of soldering materials and three different assembly procedures were used for assembly of PoP system. The reliability properties of assembled PoP systems were investigated using accelerated aging and periodic resistance measurements of daisy-chain solder joints systems. The purpose of such approach was to determine which soldering material (flux or solder paste) as well as which assembly process parameter (dipping depth of upper component in soldering material), would provide better reliability properties of the solder joints in the PoP system.
Findings
It was stated that both selected flux and solder paste dedicated to assembly of PoP systems can be utilized in soldering of PoP applications. More reliable PoP systems applications require larger attention regarding materials selection and assembly parameters. It is recommended 50 per cent dipping depth of ball’s height into soldering material during upper PoP component assembly for more reliable applications. For less demanding PoP systems, the process window from 30 up to 70 per cent is acceptable. All observed failures after thermal shocks occurred in upper PoP components.
Originality/value
This paper explains how materials and assembly parameters have influence on lead-free solder joints reliability in PoP systems. Especially, influence of process window for dipping procedure of upper components balls into soldering material was presented.
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Janusz Sitek, Aneta Araźna, Kamil Janeczek, Wojciech Stęplewski, Krzysztof Lipiec, Konrad Futera and Piotr Ciszewski
– The purpose of this paper is to evaluate the reliability of solder joints made on long FR-4 and metal core printed circuit boards using the accelerated thermal cycling.
Abstract
Purpose
The purpose of this paper is to evaluate the reliability of solder joints made on long FR-4 and metal core printed circuit boards using the accelerated thermal cycling.
Design/methodology/approach
Solder joints of diodes and resistors samples made on long FR-4 and aluminum (Al) core printed circuit boards were examined. Two kinds of solder pastes were used for the samples preparation. All samples were subjected to temperature aging cycles (−40°C – 3 hours/+85°C – 3 hours). Solder joints resistance, X-Ray inspection and metallographic cross-sections for samples as received and after 100, 500 and 1,000 hours of thermal cycles were utilized for solder joints assessment.
Findings
It was stated that 1,000 hours of thermal cycles were enough to show reliability problems in solder joints on long and/or AL core printed circuit board assembly (PCBA). The solder joints of R1206 components were the most sensitive reliability elements. The solder joints of LED diodes are more reliable than solder joints of R1206 resistors. Solder joints made on FR-4 substrate were about two times more reliable than ones on AL core substrate. Cracks in solder joints were the visible reason of solder joints failures.
Originality/value
The influence of thermal cycles on the reliability of solder joints on long, FR-4 and metal core printed circuit boards were presented. Findings from this paper can be used for planning of reliability trials during validation of reflow processes of products containing long or long metal core printed circuit boards (PCBs).