Method of soldering an electronic component with a high lateral accuracy
View Patent ↗The present invention relates to a method of soldering an electronic component ( 3 ) to a substrate ( 1 ) with high accuracy using transient liquid phase soldering. The component ( 3 ) is exactly positioned above the substrate ( 1 ) with a handling tool, placed in the melted solder ( 2 ) and pressed against the substrate ( 1 ). The component ( 3 ) is then released and the solder ( 2 ) allowed solidifying. Due to the use of a solder ( 2 ) having a sufficiently high amount of a second metal or metal alloy of a higher melting point which only partly dissolves in the melted first metal or metal alloy of a lower melting point, a solid framework forms during the liquid phase soldering which inhibits a lateral movement of the placed component ( 3 ) during soldering. Since the positioning of the component ( 3 ) is made using exact reference features on the substrate ( 1 ), the whole soldering process results in a highly accurate lateral position of the soldered component.
1. A method of soldering an electronic component to a substrate by transient liquid phase soldering, the method comprising
depositing a solder paste allowing transient liquid phase soldering on contact pads of the substrate,
melting the solder paste at a temperature of the transient liquid phase soldering,
positioning the component above the substrate with a handling tool ( 4 ) using alignment features on the substrate,
pressing the component with the handling tool ( 4 ) in the melted solder paste,
releasing the component, and
allowing the melted solder paste to solidify,
wherein a solder paste is used which contains a mixture of particles of different metals and/or of metal alloy(s), at least a first metal or metal alloy of said mixture melting at the temperature of the transient liquid phase soldering and at least a second metal or metal alloy of said mixture melting at a higher temperature, metal particles of the second metal or metal alloy being included in such a high amount in the solder paste that during the transient liquid phase soldering only a portion of these metal particles of the second metal or metal alloy dissolve in the melted solder paste and an intermetallic phase forms with the melted first metal or metal alloy at the particle surface between the remaining particles, resulting in the formation of a solid framework within the melted solder paste,
wherein a portion of the metallic particles of the second metal or metal alloy is selected to comprise metallic spheres having a diameter of between 40 and 60 μm, said portion being larger than 50 wt% of the metallic particles of the second metal or metal alloy.
2. The method according to claim 1 , wherein the solder paste ( 2 ) comprises a SnAgCu alloy as the first metal alloy and Cu as the second metal.
3. The method according to claim 1 wherein a fraction of the metallic particles of the second metal or metal alloy is selected to be between 20 and 40 wt. % in relation to all metallic particles in the solder paste.
4. The method according to claim 1 , wherein said component is a light emitting diode package.