Using underfill or flux to promote placing and parallel bonding of light emitting diodes

Abstract

Embodiments relate to using flux or underfill as a trapping layer for temporarily attaching light emitting diodes (LEDs) to a substrate and heating to simultaneously bond multiple LEDs onto the substrate. The flux or underfill may be selectively coated at the ends of electrodes of the LEDs prior to placing the LEDs on the substrate. Due to adhesive properties of the flux or underfill, multiple LEDs can be placed on and attached to the substrate prior to performing the bonding process. Once LEDs are placed on the substrate, the flux or underfill facilitates formation of metallic contacts between electrodes of the LED and contacts of the substrate during the bonding process. By using the flux or underfill, the formation of metallic contacts can be performed even without applying pressure.

1 . A light emitting assembly comprising:
 a substrate with contacts on a side of the substrate; and   a plurality of light emitting diodes (LEDs) having electrodes connected to the contacts of the substrate by metallic contacts, a metallic contact for a first light emitting diode (LED) die formed by:
 placing at least the first LED die on the substrate with a flux or underfill as a trapping layer between an electrode of the first LED die and a contact of the substrate; and 
 heating the contact, the electrode, and the flux or underfill to form the metallic contact between the first LED die and the substrate. 
   
     
     
         2 . The light emitting assembly of  claim 1 , wherein forming the metallic contact further comprises detaching a pick-up head for placing the first LED die on the substrate from the first LED die after placing the first LED die on the substrate, adhesive forces of the flux or underfill securing the first LED die on the substrate during detaching of the pick-up head from the first LED die. 
     
     
         3 . The light emitting assembly of  claim 1 , wherein forming the metallic contact further comprises placing a second LED die on the substrate prior to the heating. 
     
     
         4 . The light emitting assembly of  claim 1 , wherein the metallic contact is formed without applying external pressure on the first LED die towards the substrate during the heating. 
     
     
         5 . The light emitting assembly of  claim 1 , wherein forming the metallic contact further comprises:
 placing a platform with an elastomer pad on the first LED die; and   applying pressure on the first LED die towards the substrate by applying pressure on the platform with the elastomer pad.   
     
     
         6 . The light emitting assembly of  claim 1 , wherein the electrode, the contact, and the flux or underfill are selectively heated by focusing laser light. 
     
     
         7 . The light emitting assembly of  claim 1 , wherein the flux or underfill is rosin. 
     
     
         8 . (canceled) 
     
     
         9 . The light emitting assembly of  claim 3 , wherein the second LED die is placed on the substrate simultaneously with the placing of the first LED die on the substrate. 
     
     
         10 . The light emitting assembly of  claim 1 , wherein the flux or underfill is provided on the electrode, and at least a tip of the electrode is coated with the flux or underfill by dipping the tip into a flux or underfill layer. 
     
     
         11 . The light emitting assembly of  claim 1 , wherein forming the metallic contact further comprises subsequent to placing the first LED die on the substrate, repositioning the first LED die to align the electrode with the contact, the flux or underfill remaining between the electrode and the contact. 
     
     
         12 . A non-transitory computer readable storage medium with instructions that, when executed by at least one processor, cause the processor to:
 align electrodes of a first light emitting diode (LED) die with contacts of a substrate, flux or underfill provided on at least the electrodes or the contacts;   place the first LED die on the substrate with the flux or underfill as a trapping layer between the electrodes and the contacts; and   heat the electrodes, the contacts, and the flux or underfill to form metallic contacts between the first LED die and the contacts.   
     
     
         13 . The non-transitory computer readable storage medium of  claim 12 , further comprising an instruction to detach a pick-up head for placing the first LED die on the substrate from the first LED die after placing the first LED die on the substrate, adhesive forces of the flux or underfill securing the first LED die on the substrate during detaching of the pick-up head from the first LED die. 
     
     
         14 . The non-transitory computer readable storage medium of  claim 12 , further comprising an instruction to place a second LED die on the substrate prior to the heating. 
     
     
         15 . The non-transitory computer readable storage medium of  claim 14 , wherein the second LED die is placed on the substrate simultaneously with the placing of the first LED die on the substrate. 
     
     
         16 . The non-transitory computer readable storage medium of  claim 12 , wherein the flux or underfill is provided on the electrodes, and at least tips of the electrodes are coated with the flux or underfill by dipping the tips into a flux or underfill layer. 
     
     
         17 . The non-transitory computer readable storage medium of  claim 12 , wherein the metallic contacts are formed without applying external pressure on the first LED die towards the substrate during the heating. 
     
     
         18 . The non-transitory computer readable storage medium of  claim 12 , further comprising instructions to:
 place a platform with an elastomer pad on the first LED die; and   apply pressure on the first LED die towards the substrate by applying pressure on the platform with the elastomer pad.   
     
     
         19 . The non-transitory computer readable storage medium of  claim 12 , wherein the electrodes, the contacts, and the flux or underfill are selectively heated by focusing laser light. 
     
     
         20 . The non-transitory computer readable storage medium of  claim 12 , wherein the flux or underfill is rosin. 
     
     
         21 . The non-transitory computer readable storage medium of  claim 12 , further comprising an instruction to, subsequent to placing the first LED die on the substrate, repositioning the first LED die to align the electrodes with the contacts, the flux or underfill remaining between the electrodes and the contacts.