Patent EP-3951842-A2 (EP)
Inventor: HEINRICH ALEXANDER
IPC: H01L21/60
Filed: 2021-07-26
Abstract: A pre-soldered circuit carrier (100) includes a carrier having a metal die attach surface (108, 132, 140), a plated solder region (114) on the metal die attach surface (108, 132, 140), wherein a maximum thickness of the plated solder region (114) is at most 50 µm, the plated solder region (114) has a lower melting point than the die attach surface (108, 132, 140), and the plated solder region (114) forms one or more intermetallic phases (122) with the die attach surface (108, 132, 140) at a soldering temperature that is above the melting point of the plated solder region (114). 
     A method of forming a pre-soldered element comprises: providing a substrate (100) comprising a first metal joining surface (108, 132, 140); depositing a mask material (110) on the substrate (100) that covers the first metal joining surface (108, 132, 140); patterning the mask material (110) to form an opening (112) that exposes the first metal joining surface (108, 132, 140); and performing a plating process (e.g., an electroplating process or an electroless plating process) that forms a plated solder region (114) on a portion of the first metal joining surface (108, 132, 140) that is exposed by the opening (112); wherein the plated solder region (114) has a lower melting point than the first metal joining surface (108, 132, 140), and wherein the plated solder region (114) forms one or more intermetallic phases (122) with the first metal joining surface (108, 132, 140) at a soldering temperature that is above the melting point of the plated solder region (114), wherein a maximum thickness of the plated solder region (114) may be at most 50 µm. 
     A method of soldering electronic components comprises: providing a substrate (100) comprising a first metal joining surface (132) and a joining partner (116, 124, 126, 128) comprising a second metal joining surface, the substrate (100) or the joining partner (116, 124, 126, 128) being pre-plated with a plated solder region (114); arranging the joining partner (116, 124, 126, 128) and the substrate (100) together such that the plated solder region (114) interfaces with the first metal joining surface (132) and with the second metal joining surface; and performing a pressure-free diffusion soldering step that forms a first soldered joint (120, 136) between the first and second metal joining surfaces and the plated solder region (114), wherein a maximum thickness of the plated solder region is at most 50 µm, and wherein the soldering step is performed at a soldering temperature that causes the plated solder region (114) to melt and react with the first and second metal joining surfaces to form one or more intermetallic phases (122) within the first soldered joint (120, 136), each of the one or more intermetallic phases (122) having a melting point above the plated solder region (114) and the soldering temperature. 
     The pre-soldered circuit carrier or substrate (100) may comprise a dielectric layer (102) and a metal layer (104) attached to the dielectric layer (102), the metal layer (104) comprising one or more bond pads (106), wherein the die attach surface (108) is from one of the one or more bond pads (106). Alternatively, the pre-soldered circuit carrier or substrate (100) may be a leadframe comprising a die pad (130), wherein the die pad (130) comprises the die attach surface (132). Still alternatively, the substrate (100) may be a metal clip (134), wherein the first metal joining surface (140) is a die attach surface of the metal clip (134). The joining partner may be a semiconductor die (116, 124, 126), a passive electrical component or a mechanical connector (128). The plating step and the diffusion soldering step for the mechanical connectors (128) and first and second semiconductor dies (124, 126) may be performed simultaneously such that these soldered connections are formed at the same time. Alternatively, the soldered connections between the mechanical connectors (128) and the substrate (100) may be provided by a separate soldering process, which may involve conventional soldering techniques, e.g. by applying a solder paste and reflowing the solder paste and which can be performed at a temperature that is sufficient to reflow the solder for the mechanical connectors (128) but below the melting point of the intermetallic phases (122) present within the first soldered joints (120).