A lead free joining technology for high temperature interconnects using Transient Liquid Phase Soldering (TLPS)

Abstract

This Paper reports an emerging lead-free joining technology for high temperature application, which can be used for operating temperatures above 200 °C. It is called: “Transient Liquid Phase Soldering (TLPS)”. The TLPS paste used contains a tin-copper powder mixture and is almost completely transformed into Cu6Sn5 and Cu3Sn intermetallic phases after soldering. Due to the reaction between the liquid tin and the copper powder a skeleton of intermetallic phases are formed immediately during soldering and prevents the paste from collapsing so that a lot of voids remain in the solder line. The challenge for this investigation was to understand the mechanism of the skeleton formation, describe them in detail and find possibilities to avoid the skeleton formation. In this paper a new TLPS paste and two processes are described as a means to manufacture an almost void-less joint. Furthermore, a model was developed that describes the TLPS process in detail. The activation of the TLPS joint is crucial and will be described. Temperature cycling results, failure mechanisms and conclusions to increase the lifetime as well as reliability of such TLPS interconnects will be presented in this paper

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

“…Plating assisted TLP Plated balls Cu-Sn Sn plated Cu, pressure less [57] Thermal gradient TLP IMC layer Cu-Sn IMC layer [58] Solder paste TLP Paste Cu-Sn Solder paste [59] Sintering assisted TLP Residue Cu-Sn Sn-residue [60] Sintering assisted TLP Activated paste Cu-Sn Formic acid-solder paste [61] The melting point inhibitors such as Ag, Cu, or Ni in Sn do not have high diffusivity in solid base Cu, and it takes a longer time for isothermal solidification. The major Sn-based solder systems include Sn-3.5Ag, Sn-0.7Cu, and Sn-3.0Ag-0.5Cu.…”

“…Most widely used meting point depressants are pure C, B, or phosphorus as an interstitial element to reduce the isothermal solidification time [35,64,68]. Notable reduction in TLP bonding time has been obtained, to yield a very short 10 to 15 min, which covers the entire isothermal solidification and composition homogenization duration [35,[52][53][54][55][56][57][58][59][60][61][62][63][64]. More recently, the use of Sn coated Cu powders or Sn-Cu coated carbon nanotubes has been documented in past research.…”

Investigations of selected influencing process factors for transient liquid phase soldering (TLPS) as a die-attach method for automotive power modules

“…The tin layer is realized with a standard SnAgCu solder paste [6]. Alternative ways are solder pastes with copper balls inside or a copper paste with a solder deposit next to the chip [7]. Furthermore, very thin Sn-Cu preforms can be used [8].…”

“…The layered preform including a copper core with thin tin layers (Sn-Cu-Sn) has a lot of potential to achieve thin intermetallic phases with a good heat transfer at once. Previous investigations had a look on the assembly technique in general, because the application of solder paste with copper balls in it needs a special treatment and is complex to realize [7]. Other publications investigated the soldering parameters with particular attention on vacuum process steps and the pressure inside the soldering chamber with air pressure up to 240 kPa [8].…”

Advanced packaging methods for high-power LED modules

“…Transient liquid phase soldering is an approach with the goal to do assembly with standard pick and place equipment in a quick reflow process [12][13][14][15][16]. For this purpose standard Sn-based solder paste will be supplemented with copper powder (Fig.…”