Abstract:
A method for making EMI shielding layer on a package is disclosed to include the steps of: a) disposing a UV curable adhesive which can be thermally released on a light-transmissive substrate; b) placing the package on the UV curable adhesive in such a way that the UV curable adhesive adheres to and cover a surface of the package having solder pads; c) irradiating UV light toward the light-transmissive substrate to cure the UV curable adhesive; d) forming an EMI shielding layer on the package; and e) thermally releasing the UV curable adhesive.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to EMI shielding technology, and more particularly, to a method for making an EMI shielding layer on a package, which prevents EMI shielding layer from peeling off or scratching. 
     2. Description of the Related Art 
     In a conventional SiP (System in package) module, the outer surface of the package is usually coated with an EMI shielding layer for shielding electromagnetic noises. However, in the conventional process of making the EMI shielding layer, multi-strip or multi-panel designs are usually adapted. At this time, adjacent packages may be connected to each other by the EMI shielding layer, so that an external force should be applied to separate each of the connected packages. When separating the packages, a part of the EMI shielding layer may be peeled off, or burrs and chips may be produced and adhered to the EMI shielding layer or the package, resulting in poor package appearance and shorting between the EMI shielding layer and the solder pads. Therefore, it is desirable to provide a method for making EMI shielding layer on a package, which can avoid producing burrs and chips during formation of the EMI shielding layer on the package. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is a main object of the present invention to provide a method for making EMI shielding layer on a package, which avoids producing burrs and chips, and prevents shorting between the EMI shielding layer and the solder pads. 
     To achieve this and other objects of the present invention, a method for making EMI shielding layer on a package is provided to have the following steps: step a) disposing a thermal releasable UV curable adhesive on a light-transmissive substrate; step b) placing the package on the UV curable adhesive in such a way that the UV curable adhesive adheres to a bottom surface of the package having solder pads to cover the solder pads; step c) irradiating UV light toward the light-transmissive substrate to cure the UV curable adhesive; step d) forming an EMI shielding layer on the package; step e) thermally releasing the UV curable adhesive. 
     Thus, the solder pads on the bottom surface of the package are covered by the UV curable adhesive, preventing shorting between the EMI shielding layer and the solder pads during formation of the EMI shielding layer on the package. Further, during the process of thermally releasing the UV curable adhesive, the UV curable adhesive will exert a force to the EMI shielding layer on a lateral side surface of the package. The force exerted to the EMI shielding layer is uniformly distributed and slowly generated, avoiding producing burrs and chips on the EMI shielding layer. 
     In one aspect, when the package is placed on the UV curable adhesive, the UV curable adhesive is also adhered to the lateral side surface near the bottom of the package. This measure can effectively prevent shorting between the EMI shielding layer and the solder pads during the formation of the EMI shielding layer. 
     In another aspect, the invention employs a sputtering process to form the EMI shielding layer. Further, the sputtering temperature is controlled at a temperature, e.g. 170° C., that is lower than the temperature in thermally releasing the UV curable adhesive, preventing the UV curable adhesive, which is originally aimed to cover the solder pads, from thermal releasing during the sputtering process. 
     In another aspect, in the step of thermally releasing the UV curable adhesive, it is optioned to place the package in a high temperature liquid, enabling the UV curable adhesive to be thermally expanded and thermally released from the package. 
     Other and further benefits, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart of a method for making EMI shielding layer on a package in accordance with a preferred embodiment of the present invention; 
         FIG. 2  is a top view of a light-transmissive substrate in accordance with the present invention, illustrating the distribution of the disposing zones; and 
         FIGS. 3A-3E  are schematic sectional views illustrating the fabrication of the EMI shielding layer of the package in accordance with the present invention 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-3 , in order to facilitate understanding the benefits, advantages and features of the present invention, the invention provides a preferred embodiment in conjunction with the accompanying drawings, in which a package strip (or package panel, not shown) comprising a plurality of packages  10  of SiP (System in Package) module is used as an example. The SiP module can be, but not limited to, Fan out SiP or Embedded SiP. With respect to the structure of each package  10  of the package strip (or package panel), please refer to  FIG. 3B . As illustrated, the package  10  comprises a substrate  11 , and a molding layer  13  located on a top of the substrate  11 . The substrate  11  has a grounding layer  14  and a plurality of solder pads  110  arranged on a bottom surface  15  thereof for enabling the package  10  electrically connected to external electronic devices. The details of each step are described hereinafter: 
     Step S 1 : Disposing a ultraviolet (abbreviated to UV hereafter) curable adhesive  30 , which can be thermally released, on a top surface of a light-transmissive substrate  20  (see  FIG. 3A ). In this embodiment, a light-transmissive glass is used for the light-transmissive substrate  20 . The light-transmissive substrate  20  herein called is a substrate  20  that at least admits UV light to transmit and propagate inside the substrate  20 . Referring also to  FIG. 2  and  FIG. 3A , the top surface of the light-transmissive substrate  20  is divided into a plurality of disposing zones  21 . These disposing zones  21  are arranged in, but not limited to, a 5×4 array. Each disposing zone  21  is evenly disposed with a layer of UV curable adhesive  30  having a thickness of 100 μm. The disposed area is larger than the area of the bottom surface  15  of the substrate  11 . Further, in this embodiment, the UV curable adhesive  30  is selected from the product from VALTRON® company with the product model of AD4600 or AD4601 that can be cured within a few seconds after UV light exposure, and the UV curable adhesive  30  can be debonded, thermally expanded and then thermally released from the adhered object when placed in a hot liquid or in a high temperature environment over 170° C. 
     Further, in Step S 2 , Perform a singulation process to form the plurality of packages  10  from the package strip (or package panel). 
     Step S 3 : Use a pick and place machine to pick up each singulated package  10  and then place each singulated package  10  on the UV curable adhesive  30  to each respective coating zone  21 , enabling the bottom surface  15  with the solder pads  110  of the package  10  to be completely adhered to and covered by the UV curable adhesive  30  (see  FIG. 3B ). Further, in the present embodiment, the UV curable adhesive  30  is adhered to the lateral side surface  17  near the bottom of the package  10  in a height of 30 μm from the bottom of the package  10 , facilitating formation of the EMI shielding layer  50  on the package  10  in the follow-up steps to prevent from shorting and bridging between the EMI shielding layer  50  and the solder pads  110  of the package  10 . 
     After step S 3 , Step S 4  is performed. S 4 : Use a lamp  40  to irradiate UV light toward an surface of the light-transmissive substrate  20  which does not dispose the UV curable adhesive  30  to cure the UV curable adhesive  30  (see  FIG. 3C ). In this embodiment, the lamp  40  can be, but not limited to, mercury vapor bulb. 
     After step S 4 , Step S 5  is performed. S 5 : Form an EMI shielding layer  50  on the package  10 , enabling the EMI shielding layer  50  to be electrically connected with the grounding layer  14 , as shown in  FIG. 3D . In this embodiment, the EMI shielding layer  50  is formed by a sputtering process. In the sputtering process, the desired EMI shielding layer  50  is formed on an outer surface of the molding layer  13  of the package  10 , the lateral side surface of the substrate  11  and a part of an outer surface of the UV curable adhesive  30 . It is noted that the temperature in the sputtering process is controlled at about 170° C. that is lower than the temperature in thermally releasing the UV curable adhesive  30 , preventing the UV curable adhesive  30 , which is originally aimed to cover and shield the solder pads  110  of the package  10 , from thermal releasing. 
     Thereafter, perform Step S 6 . S 6 : Thermally release the UV curable adhesive  30  by, for example, placing the package  10  which is covered by the UV curable adhesive  30  in a high temperature liquid for enabling the cured UV curable adhesive  30  to thermally release from the package  10 . In this present embodiment, the package  10  covered by the UV curable adhesive  30  is placed in a high temperature liquid in a temperature higher than 170° C. for enabling the cured UV curable adhesive  30  to be thermally released from the package  10 . At this moment, the UV curable adhesive  30  on the bottom surface  15  and the lateral side surface  17  near the bottom of the package  10  is thermally expanded and then peeled off from the package  10 . During the thermal release process, the EMI shielding layer  50  close to the bottom of the lateral side surface  17  will also be disconnected due to the peeling of the UV curable adhesive  30 , causing separation among the package  10 , the UV curable adhesive  30  and the light-transmissive substrate  20 . The separated package  10  is shown in  FIG. 3E . 
     It is to be noted that, prior to Step S 5  to form the EMI shielding layer  50 , the UV curable adhesive  30  is cured to cover all of the bottom surface  15  (including the solder pads  110 ) of the package  10 , preventing shorting and bridging between the EMI shielding layer  50  and the solder pads  110  in the follow up step of forming the EMI shielding layer  50 . Further, because the UV curable adhesive  30  is covered on the lateral side surface  17  near the bottom of the package  10  in Step S 3 , at least 30 μm height of the lateral side surface  17  from the bottom of the package  10  is not disposed with the EMI shielding layer  50 . Thus, a clearance S is left between the bottom surface  15  of the package  10  and the EMI shielding layer  50  after Step S 6 , as show in  FIG. 3E , effectively lowering the possibility of shorting and bridging between the EMI shielding layer  50  and the solder pads  110 . 
     Further, in this embodiment, in step S 6 , the UV curable adhesive  30  is heated to expand in a high temperature liquid. The force exerted by the thermal expansion of the UV curable adhesive  30  on the EMI shielding layer  50  is uniformly distributed and slowly generated, avoiding producing burrs and chips.