Patent Application
20140000804
1. Technical Field
The present disclosure is directed to methods and apparatus of using light to fix a component placed over light-curable adhesives during assembly.
2. Description of the Related Art
Some semiconductor assembly operations are performed in stages in various locations in a building. The mounting or bonding of discrete components to a substrate requires transferring or moving the substrate between several stations.
A pick-and-place system 20, as illustrated in
Semiconductor manufacturers often use light-curable adhesives as a means to bond a component to a substrate, because it offers tremendous benefits in certain situations. The light-curing process for these adhesives is relatively fast as most light-curable adhesives cure fully in less than 30 seconds, thereby allowing shorter cycle time, increased capacity, and better automation. Further, light-curable adhesives create strong bond strength and can bond dissimilar substrates. Light-curable adhesives are also environmentally sensitive since they can be cured by solvent-free photopolymerization, and the energy required for curing is lower than other technologies. Light-curable adhesives are often preferred for process automation as they do not cure unless exposed to light, and they do not get cured gradually during preservation. Light-curable adhesives are used in many heat-sensitive electronics since the processing time is short, allowing control over the rise of temperature of the target object. Ultraviolet (UV) light-curable adhesive, also known as UV glue, is one example of light-curable adhesives.
UV curing is the process of changing a monomer (liquid) to a polymer (solid) with the exposure to UV light. Generally, a UV light curable adhesive consists of monomer, oligomer, photopolymerization initiator and various additives. The photopolymerization initiator is excited by the absorption of UV light and reacts with other components through decomposition to eventually change the material exposed to the UV light from liquid to solid. Different photopolymerization initiator reacts to different ranges of UV light, so a UV light is selected to match the adhesive to be cured. UV-A is the most common light used for curing UV light adhesives. When used to cure a UV adhesive, a UV radiation is generally measured by its irradiation intensity per unit area (for example, in mW/cm2). The amount of UV exposure (Intensity x Irradiation time) needed for curing depends on the material itself and generally, higher intensity leads to faster cure.
Other light-curable adhesives can be used as well, such as those curable through exposure to visible light.
A light-curing is usually a later stage of the electronics product assembly line. Once components have been placed on a substrate, the substrate is moved into a closed light-curing chamber or through a light-curing conveyor. During this stage, the light-curable adhesive is exposed to the appropriate curing light and become fully cured.
The present disclosure relates to fixing a component to a substrate to prevent the component from shifting. A light source is coupled to a pick-and-place head, and the light is transmitted on a component placed over a light-curable adhesive. As the light-curable adhesive begins to cure, it holds the component in place on the substrate. The light is transmitted through the opening of an aperture through which a vacuum is introduced to pick and place a component.
In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the disclosure. However, one skilled in the art will understand that the disclosure may be practiced without these specific details. In some instances, well-known structures associated with semiconductor manufacturing and assembly process have not been described in detail to avoid obscuring the description of the embodiments of the present disclosure.
Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.”
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
In the drawings, identical reference numbers identify similar features or elements. The size and relative positions of features in the drawings are not necessarily drawn to scale.
In
To pick a component, the pick-and-place head 100 is first positioned over the component 118, then it is lowered such that the second opening 116 comes in contact with the component 118. A vacuum is introduced to the vacuum path 106, creating a suction force that causes the component 118 to be affixed the second opening 116. The pick-and-place head 100 is then raised up and positioned to the location onto which the component is to be placed, the location where light-curable adhesive 120 is already applied on a substrate 122. With the vacuum still introduced, the pick-and-place head 100 is lowered toward the substrate 122 until the component 118 that is affixed to the second opening 116 comes to rest on the light-curable adhesive 120.
A light is subsequently directed through the optical fiber 104 and the tip 108 of the optical fiber transmits the light through the second opening 116 of the aperture 114 on component 118 for a selected period of time. This causes the light-curable adhesive under the component 118 to begin to cure and hold the component 118 in place.
The required light exposure to cure a light-curable adhesive depends on the light intensity and the adhesive material itself. UV adhesives generally need between 250 ms and 1 second of UV light exposure to become partially cured, and between 5 seconds and 30 seconds to become fully cured. Depending on the type of adhesive and the intensity of the light, the period of light exposure is selected to be as short as practical in order to ensure that the component is at least partially fixed so that it does not shift or become otherwise disturbed when the substrate is moved to the next stage. In one embodiment, a light is transmitted for 500 ms to partially cure the light-curable adhesive. In another embodiment, a light is transmitted for 5 to 30 seconds to fully cure the light-curable adhesive. Having the light-curable adhesive fully cured during the pick-and-place stage may eliminate the need to move the substrate to another stage for additional curing, and this may be desirable when there are only a few components to be bonded to a substrate. However, if there are hundreds of components to be bonded on a substrate, the cumulative time it takes to fully cure each component individually may be prohibitive. For 400 components, for example, it would take more than 30 minutes of curing. It may be more efficient in this case to only partially cure the light-curable adhesive after each component is placed, then move the substrate to the next stage to fully cure all the components concurrently. In this later approach, individual partial curing of all 400 components would take less than 4 minutes, and the full curing for the whole substrate would be in the range of 5 to 30 seconds, depending on the type of adhesive and the intensity of the light. The specific numbers set forth here are meant to be examples as it is known in the art that the curing profile, thus curing time, for a light-curable material depends on the light intensity used.
At the conclusion of at least partial curing of the light-curable adhesive, the pick-and-place head 100 may be moved away from the component 118 to pick and place another component.
The optical fiber 104 may be a fiber optic strand for carrying an ultraviolet light or other visible lights. There are a variety of light-curable adhesives, and each of them may require a light of certain wavelength for curing. Different light sources, therefore, may be used and the most appropriate optical fiber 104 may be selected accordingly.
There are at least two possible techniques to combine the vacuum delivery source and the optical fiber. In one embodiment, illustrated in
In a preferred embodiment, a UV light source is guided over an optical fiber strand that is 6 mm in diameter. The optical fiber strand is coupled to the third opening of the aperture at a distance of 3 mm from the second opening 116 of the aperture 114. A diameter of the second opening 116 of the aperture 114 may be selected to provide a desired light intensity. The following table shows some of the possible diameters of the second opening 116 and the associated intensities of the light leaving the second opening 116 when the UV light source is transmitted at 90% intensity.
In an alternative embodiment, the light is be transmitted, step 206, onto the just-placed component for a length of time selected to fully cure the light-curable adhesive on which the component was placed. An ultraviolet light may be transmitted for 5 to 30 seconds to fully cure a UV adhesive. In this alternative embodiment, the substrate does not need to be moved to the next stage for full curing anymore.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
