Recent Progress in Transient Liquid Phase and Wire Bonding Technologies for Power Electronics

metals Review Recent Progress in Transient Liquid Phase and Wire Bonding Technologies for Power Electronics Hyejun Kang 1, Ashutosh Sharma 2 and Jae Pil Jung 1,* 1 Department of Materials Science and Engineering, University of Seoul, 163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 02504, Korea; [email protected] 2 Department of Energy Systems Research and Department of Materials Science and Engineering, Ajou University, Suwon 16499, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-2-6490-2408 Received: 8 June 2020; Accepted: 7 July 2020; Published: 11 July 2020 Abstract: Transient liquid phase (TLP) bonding is a novel bonding process for the joining of metallic and ceramic materials using an interlayer. TLP bonding is particularly crucial for the joining of the semiconductor chips with expensive die-attached materials during low-temperature sintering. Moreover, the transient TLP bonding occurs at a lower temperature, is cost-effective, and causes less joint porosity. Wire bonding is also a common process to interconnect between the power module package to direct bonded copper (DBC). In this context, we propose to review the challenges and advances in TLP and ultrasonic wire bonding technology using Sn-based solders for power electronics packaging. Keywords: power module; TLP bonding; wire bonding; brazing; die-attached materials 1. Introduction Due to rapid progress in power electronics and packaging devices, there is a strong demand for better joining materials and processes. However, conventional silicon power module devices are now being replaced with high power ceramic modules made of SiC or AlN packages, which have better thermal stability at higher temperatures [1]. Thinner die packages combined with high speed and density require new packaging materials to support the device applications [2]. The power module is an essential component of power electronics for performing power conversion and supply or switching supply while maintaining stability and efficiency [3]. All power modules are used in inverter or converter circuits of on-board devices, but their types vary depending on the circuit configuration and the specifications of the modules [4]. The popular insulated gate bipolar transistor (IGBT) power module package used for power conversion is shown in Figure1. It consists of several components, e.g., heat sink, base plate, and direct bonded copper (DBC) substrate with attachment material [3–5]. The top side of the module has wire-bonded elements connected to an IGBT diode and the external lead frames. The IGBT is bonded to the DBC with die attachments, as shown in Figure1. The IGBT module is generally encapsulated with multiple diodes, metal-oxide field-effect transistors (MOSFETs), and intelligent power modules (IPMs) for the surface protection of wire bonds from the external atmosphere. These power semiconductors are generally bonded with a die attach material or soldered to the DBC substrate for electrical and thermal contact and insulation when necessary. In modern versions of power modules, the IPM mounts a dedicated circuit for drawing maximum power from the IGBT and minimizing electromagnetic shielding effect for the protection of the entire device. Metals 2020, 10, 934; doi:10.3390/met10070934 www.mdpi.com/journal/metals Metals 2020, 10, 934 2 of 21 Metals 2020, 10, x FOR PEER REVIEW 2 of 23 FigureFigure 1. 1.Schematic Schematic diagram diagram of of a powera power module. module. Recently,theRecently, the development development of high-reliability,high-e of high-reliability,ffi ciencyhigh-efficiency power devices power suitable devices for eco-friendlysuitable for applicationseco-friendly such applications as electric vehiclessuch as electric or hybrid vehicles vehicles or has hybrid attracted vehicles much has attention. attracted Likewise, much attention. interest inLikewise, high-reliability interest power in moduleshigh-reliability is also growing power among modules electronic is also manufacturers. growing Theamong enhancement electronic inmanufacturers. the reliability of The the powerenhance modulesment in is the directly reliability related of to the the power highly modules reliable wire is directly bonding related technology to the andhighly joining reliable process wire for bonding the die attachment technology over and the joining semiconductor process for insulated-gate the die attach bipolarment transistor over the (IGBT)semiconductor [5,6]. The insulated primary-gate bonding bipolar methods transistor for power(IGBT) modules[5,6]. The include primary Ag bonding and/or Cumethods powder for sinteringpower modules [7], Sn-based include transient Ag and/or liquid Cu phase powder (TLP) sintering bonding [7], [8 ,9Sn],- etc.,based while transient Al wire, liquid Al-0.5Cu phase wire,(TLP) andbonding Al-0.005Ni [8,9], wireetc., arewhile used Al forwire, wire Al bonding.-0.5Cu wire Various, and Al - wires0.005Ni are wire used are in used the form for wire of Al bonding. ribbon, Cu-AlVarious clad Al ribbon, wires are and used Cu wires in the [ 10form,11]. of Al ribbon, Cu-Al clad ribbon, and Cu wires [10,11]. ItIt is is also also to to be be noted noted that that in in modern modern power power module module circuits circuits and and assemblies, assemblies, various various metallic metallic conductorsconductors are are also also needed needed to beto joinedbe joined to the to ceramicthe ceramic dies anddies circuitsand circuits [12–14 [12]. Various–14]. Various authors authors have suggestedhave suggested the use of the active use metal of active soldering metal and soldering/or brazing and/or or low-temperature brazing or Zn-basedlow-temperature soldering Zn [15-–based18]. solderingVarious [15 Zn-based–18]. solders, such as Zn6Al, Zn6Al1Ga, Zn3Al3Mg, and Zn4Al3Ga3Mg, have been used asVarious lead-free Zn alternatives-based solders, by Rettenmayr such as Zn et6Al, al. Zn [196].A However,l1Ga, Zn3Al such3Mg types, and ofZn solders4Al3Ga3 areMg, associated have been withused high as brittlenesslead-free duealternative to the temperatures by Rettenmayr dependence et al. of [ Ga19]. solubility However, in Znsuch as welltype ass theof solders formation are ofassociated Ga compounds with hi richgh brittleness in Al and due Zn. to This the t brittlenessemperature of dependence solder can beof Ga avoided solubility by decreasing in Zn as well the as solubilitythe formation at higher of temperatures.Ga compounds rich in Al and Zn. This brittleness of solder can be avoided by decreasingShimizu the et al. solubility [20] used at various higher additivetemperatures. elements (Sn, In, and Ge) to the Zn4Al3Mg and Zn6Al5Ge alloys toShimizu replace Pb-5Snet al. [2 solder0] used for die-attachedvarious additive applications elements [20 ].(Sn, Although In, and a good Ge) die-attachingto the Zn4Al property3Mg and wasZn6 observedAl5Ge alloys at higher to replace temperatures, Pb-5Sn thesolder addition for ofdie Sn,-attach In, anded Gaapplications deteriorated [20 the]. Although workability a andgood stressdie-attaching relaxation property ability of was this alloy.observed In another at higher study, temperature Cheng et al.s, [the21] showedaddition that of theSn, additionIn, and ofGa Sndeteriorated to Zn4Mg3 Althe alloys workability caused and a reduction stress relaxation of uniaxial ability tensile of this strength alloy. withIn another increasing study, temperature. Cheng et al. The[21 elongation] showed ratiothat wasthe pooraddition at 200 of◦ CSn but to improveZn4Mg3Al at 100alloys◦C comparedcaused a toreduction room temperature. of uniaxial tensile strengthCeramics with such increasing as sapphire temperature. were bonded The elonga directlytion by ratio ultrasound-assisted was poor at 200 soldering°C but improve by Sn10 atZn 1002Al °C soldercompared by Cui to et room al. [22 temperature.]. The bond formation was noticed by the presence of a nanocrystalline alumina layer onCeramics the Sn-Zn-Al such as/sapphire sapphire interface were bonded while reflowingdirectly by at ultrasound 230 ◦C. -assisted soldering by Sn10Zn2Al solderActive by metalCui et brazing al. [22 has]. The been bond used formation regularly towas braze noticed ceramics by the to metalspresence in various of a na applications.nocrystalline Pioneeringalumina layer work on on the ceramic Sn-Zn- metalAl/sapphire bonding interface was done while by reflowing Jung et al. at[ 23023]. °C Active. brazing generally includesActive Ag-Cu metal eutectic brazing with thehas addition been used of Ti orregularly Nb, which to promotesbraze ceramics wetting to [23 ,metals24]. Additionally, in various recentapplications. high entropy Pioneering alloys work have on also ceramic been tested metal forbonding their joiningwas done applications, by Jung et al and. [2 experiments3]. Active braz areing underwaygenerally byincludes several Ag researchers-Cu eutectic [25 ].with High the entropy addition alloys of Ti have or Nb shown, which impressive promotes properties wetting due[23, to24]. theirAdditiona high mixinglly, recent entropy, high which entropy favors alloys the formation have also of solidbeen solutiontested for phases their compared joining applications to intermetallic, and compounds.experiments However, are underway these alloysby several are still resea atrchers the beginning [25]. High stage entropy in the alloys field ofhave microjoining shown impressive [26]. propertiesAlthough due there to their are various high mixing active entropy reports, on which power favors modules, the formation there is not of yet solid enough solution literature

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