Patent Application
20110114258
The invention relates to the bonding of electronic devices, and in particular to adhesive dispensers using pins or stamps for printing viscous or paste-like liquid such as epoxy used in the bonding of electronic devices.
Die-bonding is an important process in the packaging of integrated circuit packages. In the die-bonding process, dice that are cut from a wafer are taken out and bonded onto a substrate such as a lead frame for follow-up processes such as wire bonding and molding. Prior to bonding a die to a substrate, a paste-dispensing mechanism dispenses an adhesive agent onto the substrate. Then, a die pick-and-place mechanism of the die bonder places a die onto the substrate at the position where the adhesive agent has been dispensed. Finally, a heater is used to cure the adhesive agent so as to bond the die to the substrate.
In the electronics industry, various methods of dispensing adhesive agents have evolved to keep up with the rapid development of manufacturing needs for adhesives and conductive epoxies in a wide array of packaging assemblies. Dispensing applications have also expanded to other areas needed for new types of packaging encapsulation techniques. A wide variety of fluid materials with different viscosities are being used as adhesives, from solder paste, conductive adhesives and damming compound to fluxes, thermal paste and underfills. Various methods of dispensing are available such as stamping, stencil printing, jet-dispensing and nozzle or needle dispensing.
Stamping, which is also known as daubing or pin transfer, involves dipping a compliant tool into a reservoir of liquid adhesive and then transferring the liquid adhesive adhering to the tool onto a substrate such as a lead frame. This method is frequently used to attain very small dots or patterns of adhesive on the substrate, or when an adhesive is not suitable for dispensing through dispenser nozzles. A stamping system is illustrated in
Different types of adhesives may be required for bonding different dice onto a substrate. For instance, non-conductive adhesive may be used to bond blue and green light emitting diode (LED) dice while silver epoxy may be applied for bonding red LED dice. When a different adhesive is required, the adhesive disc 102 and the stamping pin 106 would have to be replaced accordingly to cater for the different adhesive. If the same stamping pin 106 and adhesive disc 102 are used for different adhesives, then the stamping pin 106 and the adhesive disc 102 have to be removed for cleaning before they used to transfer a different adhesive. This results in machine idle time and lengthens the operation process. Alternatively, to avoid having to remove or change any stamping pin and adhesive disc, each machine may be designated for handling one type of die or the same range of dice using the same type of adhesive. This results in increased costs due to duplication. Therefore, it would be desirable to provide a stamping system which allows the use of different adhesives while avoiding excessive machine idle time or duplicity.
It is thus an object of this invention to seek to provide a stamping system which is capable of applying different types of adhesives successively onto a substrate when multiple adhesives are in use.
According to a first aspect of the invention, there is provided a method for transferring multiple types of adhesives from a supply of adhesives to a substrate, comprising the steps of: moving a first stamping pin to a position of a first container containing a first adhesive; transferring the first adhesive with the first stamping pin from the first container to the substrate; bonding a first die onto the first adhesive; moving a second stamping pin to a position of a second container containing a second adhesive; transferring the second adhesive with the second stamping pin from the second container to the substrate; and bonding a second die onto the second adhesive
According to a second aspect of the invention, there is provided an apparatus for transferring multiple types of adhesives from a supply of adhesives to a substrate for bonding a die onto the substrate, comprising: multiple containers for the adhesives, wherein a separate container is provided for each type of adhesive; and multiple stamping pins for transferring the adhesives from the container to the substrate, wherein each stamping pin is operative to transfer a different type of adhesive to the substrate
It would be convenient hereinafter to describe the invention in greater detail by reference to the accompanying drawings which illustrate the preferred embodiment of the invention. The particularity of the drawings and the related description is not to be understood as superseding the generality of the broad identification of the invention as defined by the claims.
The present invention will be readily appreciated by reference to the detailed description of the preferred embodiment of the invention when considered with the accompanying drawings, in which:
The preferred embodiment of the present invention will be described hereinafter with reference to the accompanying drawings.
The multiple stamping pin assembly 13 comprises a rotary stamping pin holder 14 which is positionable adjacent to the rotary platform 12 and supports a plurality of stamping pins 16. The number of stamping pins 16 preferably corresponds to the number of adhesive discs 15 comprised in the rotary platform 12. Each adhesive disc may contain a different type of adhesive 18 and each stamping pin 16 may be used for dipping into one type of adhesive 18 only.
When a particular type of adhesive 18 is required, the adhesive disc 15 containing the required adhesive 18 is rotated to a pick-up position. A stamping pin 16 on the stamping pin holder 14 pre-selected for transferring the said adhesive 18 is rotated such that it is positioned at the pick-up position for picking up and transferring the adhesive 18 to a substrate located at a stamping level. Both the adhesive disc 15 and the stamping pin 16 may also move in a translational manner to the pick-up position. Otherwise, the adhesive discs 15 may be in fixed positions while the stamping pin 16 picks up epoxy at the different fixed positions of the adhesive discs 15. In another possible embodiment, the multiple stamping pins 16 may be arranged in one or more rows on a linear movable arm above the rotary platform 12 or the adhesive discs 15 may be mounted in a row. The selected stamping pin 16 on the linear movable arm can thus be positioned above the desired adhesive disc 15 to transfer the adhesive 18.
It should be appreciated that the use of the stamping system 10 for adhesives which includes the multiple stamping pin assembly 13 according to the preferred embodiments of the invention permit efficient high-volume die bonding when a mixed production involving more than one adhesive for more than one type of die is required. Interchanging either the adhesive disc 12 or the stamping pin 16 can also be automated using the above-described stamping system to hasten the process further. Machine idle time is much reduced as it is not necessary to stop the die bonder to disassemble and replace an adhesive disc 12 or a stamping pin 16 with another one. When multiple wafer loaders are in use, multiple dice can be bonded with different adhesives in a single pass. It is also not necessary to dedicate a single die bonder for use with only one adhesive to avoid having to wash, remove or replace any adhesive disc 12 or a stamping pin 16. Hence, multiple die bonders are not required when bonding different dice to a substrate. Moreover, flexibility can be achieved since more than one adhesive may be used with one die bonder using the stamping system 10.
The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.
