Abstract:
This invention discloses a process for packaging semiconductor device with external leads. The process includes comprises Step 1: providing a lead frame comprising a plurality of lead frame units connected by a plurality of metal beams, each lead frame unit comprising a die pad and a plurality of leads located on opposite sides of the die pad; adhering a semiconductor chip onto each of the die pad, and providing a plurality of metal connections for electrically connecting each chip to its corresponding leads; Step 2 providing a plastic molding material to enclose the plurality of the lead frame units, the metal beams, the chips, and at least portions of the metal connections; Step 3 removing a portion of the plastic molding material above the metal beams to expose the metal beams and portions of the leads in connection with the metal beams; and Step 4 separating each lead frame unit, forming a plurality of individual semiconductor plastic package components with external leads.

Description:
FIELD OF INVENTION 
     This invention generally relates to the field of semiconductor device package and packaging process. More particularly, the present invention is related to a semiconductor package configuration and manufacturing method by packaging the semiconductor components with external leads. 
     BACKGROUND OF THE INVENTION 
     The conventional technologies for packaging the semiconductor components are still faced with limitations due to the facts that the packaging processes require longer processing time and higher fabrication costs. The limitations of the conventional technologies can be illustrated by the processes of packaging the semiconductor components  3  with external leads  122  as shown in  FIG. 1 . The packaging processes include the following steps:
     Step 1 Chip adhering: for each lead frame unit on a lead frame, a plurality of chips are respectively adhered to the die pads; in which the lead frame contains a plurality of lead frame units, and each lead frame unit contains die pads and a plurality of leads on both sides of the die pad; adjacent lead frame units are connected by connecting each lead to the metal beam;   Step 2 Wire connecting and bonding: for each lead frame unit, its chips and leads are connected respectively by metal wire bonding;   Step 3 Plastic packaging: carry out plastic packaging of the lead frame, sealing the chips, die pads and some leads in the plastic package; in this step, a plurality of plastic package cavities are formed for each lead frame unit, which are separated by a plurality of metal beams on the lead frame; after this step, each lead is divided into a internal portion sealed inside the plastic package, and a external portion outside the package, and each plastic package cavity unit is vertically and horizontally connected by the metal beams;   Step 4 Resin flush removal: during the plastic packaging, scraps will be left in the area at the edge of plastic package or among the external leads, so in this step the scraps formed at the edge of each plastic package cavity are removed;   Step 5 Sawing &amp; separation: saw off the metal beams among plastic package cavities by impact extrusion, separate the connection among the leads of each lead frame unit, and in the meantime keep all the lead-external portions outside the package, thus forming a plurality of individual semiconductor component products with external leads.   

     However, the processes to package the semiconductor components with external leads as described above have the disadvantages typically encountered in the processes of plastic packaging that include resin flush removal and sawing and separation. For example, in the step of plastic packaging, it is necessary to form a plurality of plastic package cavities separated by the metal beams on the entire lead frame. Another example of such disadvantages occurs in the step of separation by impact extrusion. It is necessary to prepare unique punching tool according to plastic package cavities and their pitches in order to separate the lead frame units inside each plastic package array and thus finally form a plurality of individual semiconductor components. In order to meet these unique process operation requirements to process the packaging of electronic packages to contain different types of semiconductor components with external leads, it is necessary to separately design and manufacture the processing moulds or mechanical tools, etc. that meet and realize these process requirements, thus unavoidably resulting in longer preparation period and higher manufacturing cost of the entire process. 
     Therefore, it is necessary to provide a new and improved packaging process for semiconductor components with external leads to package the semiconductor components with more convenient processing steps to simplify the manufacturing processes and reduced the production costs such that the above discussed limitations and difficulties can be resolved. It is further desirable that the new and improved processing moulds or mechanical tools, etc. can be basically applicable to general packaging process and also applicable to different types of semiconductor packaging with external leads thus effectively improving the packaging efficiency, reducing the manufacturing cost, enhancing the product quality and productivity. 
     SUMMARY OF INVENTION 
     One aspect of this invention is to provide a process for packaging semiconductor components with external leads by applying standardized processing moulds and mechanical tools. These standard processing moulds and mechanical tools can be universally applicable to package electronic devices formed as semiconductor components with different external leads without additional design and without requiring to manufacture particular operating tools including moulds, thus effectively improving plastic packaging efficiency and reducing manufacturing cost. 
     In order to achieve the above goal, the embodiments of this invention disclose a process for semiconductor packaging with external leads, including the following steps:
         Step 1: providing a lead frame comprising a plurality of lead frame units connected by a plurality of metal beams, each lead frame unit comprising a die pad and a plurality of leads located on opposite sides of the die pad; adhering a semiconductor chip onto each of the die pad, and providing a plurality of metal connections for electrically connecting each chip to its corresponding leads;   Step 2 providing a plastic molding material to enclose the plurality of the lead frame units, the metal beams, the chips, and at least portions of the metal connections;   Step 3 removing a portion of the plastic molding material above the metal beams to expose the metal beams and portions of the leads in connection with the metal beams;   Step 4 separating each lead frame unit, forming a plurality of individual semiconductor plastic package components with external leads.       

     Each lead located beside the die pad may contains an internal lead portion inside the plastic package with a lower surface exposed through the bottom of the plastic molding package and an external lead portion to be exposed outside the plastic package; In Step 2 the molding material may enclose the entire lead frame forming a plastic molding block; in Step 3 the removal of portion of molding material above the metal beams may include the process of sawing or laser blasting to form a plurality of molding material strips or blocks separated by the metal beams, with external lead portions exposed. The process in Step 3 further comprising: sawing the plastic package material vertically downward along the metal beam from the top surface of the entire plastic block down to the upper surface of the external lead portions using a first sawing tool with a first sawing width much wider than the metal beams therefore expose portions of the lead frame, including the entire metal beam and the external lead portion. 
     In one embodiment the separation of each lead frame unit in Step 4 further comprises sawing off the metal beam by a second sawing tool with a second sawing width narrower than first sawing width but slightly wider than the metal beam such that the lead connection to the metal beam is removed. 
     In one implementation method of this invention, the step of removal of a portion of the plastic molding material above the metal beam in Step 3 further comprises a step of forming a plurality of molding material strips separated by the metal beams and Step 4 further comprises the following steps:
         Step 4.1: sawing off the metal beam between adjacent plastic mold strips to separate the connection between the leads of each lead frame unit, and keep the external portion of each lead;   Step 4.2 sawing between the lead frame units of plastic package strips, to separate and form a plurality of individual semiconductor components with external leads.       

     In another implementation method of this invention, the step of removal of a portion of the plastic molding material above the metal beam in Step 3 further comprises a step of forming a plurality of molding material strips separated by the metal beams and Step 4 further comprises the following steps:
         Step 4.1 sawing between the lead frame units of plastic package strips across the metal beams with sections of metal beams connecting a plurality of lead frame units;   Step 4.2 sawing off the metal beams sections between adjacent lead frame units to separate the connection between the leads of each lead frame unit, and keep the external portion of each lead, forming a plurality of individual semiconductor components with external leads.       

     In one embodiment the external leads of adjacent leads are separately connected to the metal beam forming a space therein and the above process may further comprises a step 3.5 to remove the plastic package material filling the space between the external portions of adjacent leads by deflash or by laser blasting after Step 3; In another embodiment the external leads of adjacent leads are fused together and connected to the metal beam forming no space therein and the above process may further comprises a step 2.5 to remove the portion of metal between the external leads by masked etching or by laser cutting so that the external leads of adjacent leads are separated after package singulation. 
     The process for semiconductor packaging with external leads as provided in this invention has the following beneficial technical effects and advantages: the processing moulds and mechanical tools utilized in this method are applicable to common plastic packaging process and different types of lead-external semiconductor packaging processes, without additional design and manufacturing of particular operating tools including moulds, thus effectively improving plastic packaging efficiency and reducing manufacturing cost. 
     These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is the structural diagram of semiconductor packaging with external leads in this invention; 
         FIGS. 2A˜2F  is the top view of each step in the first specific implementation example of the process for semiconductor packaging with external leads in this invention; 
         FIGS. 3A˜3F  is the cross sectional view of each step in the first specific implementation example of the process for semiconductor packaging with external leads in this invention; 
         FIG. 4  is the flow chart of the first specific implementation example of the process for semiconductor packaging with external leads in this invention; 
         FIGS. 5A˜5F  is the top view or bottom view of each step in the second specific implementation example of the process for semiconductor packaging with external leads in this invention; 
         FIGS. 6A˜6F  is the cross sectional view of each step in the second specific implementation example of the process for semiconductor packaging with external leads in this invention; 
         FIG. 7  is the flow chart of the second specific implementation example of the process for semiconductor packaging with external leads in this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed explanation of this invention is described below by reference to of  FIG. 2˜7 , with selected embodiments as examples to illustrate the semiconductor packages according to the methods and configurations disclosed in this invention. 
     Implementation Example 1 
       FIGS. 2A˜4  show a specific implementation example of the process for packaging semiconductor device with external leads provided in this invention, which forms semiconductor components with external leads for lead frames with the following structural characteristics. 
     As shown in  FIG. 2A  and  FIG. 3A , the lead frame contains a plurality of distributed lead frame units  1 , and metal beams  2  for connecting the lead frame units. In order to clearly and concisely show the structure of the lead frame, the lead frame containing 4 lead frame units (surrounded by broken lines in  FIG. 2A ) is taken as an example in this implementation example. Wherein, each lead frame unit  1  contains a die pad  11 , and a plurality of leads  12  on both sides of the die pad  11 ; each lead contains an internal portion  121  to be sealed inside a plastic package and an external portion  122  to be exposed outside the plastic package. The external lead portions  122  of adjacent leads are separated with a space therein. Furthermore, the adjacent lead frame units  1  are connected by connecting the external portions  122  of each leads  12  to the metal beams  2 . 
     For the lead frame of above structure, as shown in  FIG. 4 , the packaging process provided in this implementation example includes the following steps:
     Step 1 Chip adhering and connection bondage: as shown in  FIG. 2B  and  FIG. 3B , for each lead frame unit  1  on the lead frame, a chip  13  is respectively adhered onto the die pad  11 , then the chip  13  and leads  12  are connected and bonded using metal wire  14 ; wherein, the metal wire can be replaced by such metal connectors as metal plate or metal strip to realize the connection among chip  13  and leads  12 .   Step 2 Plastic packaging: as shown in  FIG. 2C  and  FIG. 3C , plastic packaging of the entire lead frame is carried out, using a common packaging mould to seal all the lead frame units  1  (including chip  13 , die pad  11  and lead  12 ) in the plastic package  15  forming a block. The lower surface of leads may be exposed at the bottom of plastic package.   Step 3 Partial plastic molding material removal or first package sawing: remove the plastic package material above the metal beam  2  and the to-be-external portion  122  of each lead as shown in  FIG. 2D  and  FIG. 3D . This can be carried out by using a first thick sawing tool to saw off the plastic package material above the metal beam  2  and the external lead portion  122  of each lead, forming several plastic package strips  151  separated by the metal beam  2 ; the specific sawing method is: saw the plastic package material vertically downward along the setting direction of the metal beam  2  from the top surface of the entire plastic package  15  saw into a depth until the upper surface of the lead portion  122  of the lead frame exposed. In the production process, it is possible to estimate the downward sawing thickness by subtracting the height of the lead frame from the height of the plastic package  15 , and the required precision can be obtained in this sawing step by presetting the sawing tool with the sawing thickness.   

     In actual operation, in order to avoid insufficient saw off of the plastic package material, the estimated sawing thickness can be slightly increased to ensure that the sawing operation can be finished at once, and the surface of the entire metal beam  2  and that of each lead external portion  122  in each lead frame unit, which is connected with the metal beam  2 , can be exposed. In this process, when sawing off the plastic package material above the lead frame, even an extremely small portion downward the surface of the lead frame is saw off due to the increase of sawing thickness, the entire packaging process will not be affected. On the contrary, if an extremely small portion of plastic package material above the lead frame is not saw off after this sawing operation, it will inevitably require this sawing step to be performed again to completely remove the remaining plastic package material, thus lengthening the cycle of the entire packaging process and reducing the production efficiency. Alternatively, the plastic package molding material can be removed by laser blasting or other suitable methods. 
     Step 3.5: The process may further include a step 3.5 to remove the left behind plastic package molding material  152  disposed within the space formed between the separated external portions  122  of adjacent leads after Step 3. The plastic package material  152  disposed between the external portions  122  of adjacent leads during the plastic packaging process may be removed through deflushing. In another implementation example of this invention, the plastic package material  152  between external portions  122  of the adjacent leads can also be removed by laser beam blasting.  FIGS. 2E and 3E  are the schematic diagrams after the plastic package material  152  is saw off with plastic package material between the external portions  122  of adjacent leads removed.
     Step 4 Second package sawing: use a second thin sawing tool to saw the entire lead frame horizontally and vertically, then separate each lead frame unit  1 , forming a plurality of individual semiconductor plastic package components  3  with external leads (as shown in  FIG. 2F  and  FIG. 3F ); The specific procedure is as follows: Step 4.1. Beam sawing: vertically saw off the metal beam  2  between adjacent plastic package strips  151 , separate the connection among the leads  12  of each lead frame unit, and keep the external portion  122  of each lead; Step 4.2. Sawing: horizontally saw through between the lead frame units of plastic package strips  151 , and separate to form a plurality of individual semiconductor components  3  with external leads.   

     In another implementation example of this invention, the horizontal sawing can be done before vertical beam sawing in Step 4, i.e.: Step 4.1 Sawing: saw among the lead frame units of plastic package strips  151 ; Step 4.2. Beam sawing: vertically saw off the metal beam  2  between adjacent lead frame units, separate the connection among the leads  12  of each lead frame unit, and keep the external portion  122  of each lead, forming a plurality of individual semiconductor components  3  with external leads. 
     Implementation Example 2 
       FIGS. 5A˜7  show a specific implementation example of the process for semiconductor packaging with external leads provided in this invention, which forms semiconductor components with external leads for lead frames with the following structural characteristics. 
     As shown in  FIG. 5A  and  FIG. 6A , the said lead frame contains a plurality of distributed lead frame units  1 ′, and metal beams  2 ′ for connecting the lead frame units. In order to clearly and concisely show the structure of the lead frame, the lead frame containing 4 lead frame units (surrounded by broken lines in  FIG. 5A ) is taken as an example in this implementation example. Wherein, each lead frame unit  1 ′ contains a die pad  11 ′, and a plurality of leads  12 ′ on both sides of the die pad  11 ′; each lead contains an internal portion  121 ′ sealed inside the plastic package and an external portion  122 ′ outside the plastic package, and the external portions  122 ′ of adjacent leads are fused together. Furthermore, the adjacent lead frame units  1 ′ are connected by connecting the external portion  122 ′ of each lead  12 ′ to the metal beams  2 ′. The difference of lead frames in Implementation Example 2 from Implementation Example 1 is that external portions  122 ′ of adjacent leads are fused together without space in between and connected to the metal beam  2 ′ making metal beams  2 ′ seem wider. 
     For the lead frame of above structure, as shown in  FIG. 7 , the packaging process provided in this implementation example includes the following steps:
     Step 1 Chip adhering and connection bondage: as shown in  FIG. 5B  and  FIG. 6B , for each lead frame unit  1 ′ on the lead frame, a chip  13  is respectively adhered onto the die pad  11 ′, then the chip  13  and lead  12 ′ are connected and bonded using metal wire  14 ; wherein, the metal wire can be replaced by such metal connectors as metal plate or metal strip to realize the connection among chip  13  and leads  12 ′.   Step 2 Plastic packaging: as shown in  FIG. 5C  and  FIG. 6C , plastic packaging of the entire lead frame is carried out, using a common packaging mould to seal all the lead frame units  1 ′ (including chip  13 , die pad  11 ′ and leads  12 ′) in the plastic package  15 ′. The lower surface of leads may be exposed at the bottom of plastic package, in which  FIG. 5C  is the schematic diagram of the bottom of plastic package after sealing.   

     Step 2.5 The process may further include a step 2.5 after Step 2 to remove the metal portion between external portions of adjacent leads: the bottom of sealed plastic package  15 ′ can be etched with a mask to remove the metal between external portions of adjacent leads. In another better implementation example of this invention, the metal between external portions  122 ′ of adjacent leads at the bottom of plastic package  15  can also be removed by laser cutting. As shown in  FIG. 5D  and  FIG. 6D , wherein FIG.  5 D is the projection view of the bottom face, showing the schematic diagram after the metal between the external portions  122 ′ of adjacent leads is removed, when there is no substance among the external portions  122 ′ of adjacent leads, the plastic package material above the lead is visible through the hole opened up by the removal of the metal between the external leads  122 ′ of adjacent leads from the bottom view in  FIG. 5D . The metal beams  2 ′ become narrower.
     Step 3 Partial plastic molding material removal or first package sawing: remove the plastic package material above the metal beam  2 ′ and the to-be-external portion  122 ′ of each lead as shown in  FIG. 5E  and  FIG. 6E . This can be carried out by using a first thick sawing tool to remove the plastic package material above the metal beam  2 ′ and the to-be-external portion  122 ′ of each lead, forming a plurality of plastic package strips  151 ′ separated by the metal beam  2 ′; the specific sawing method is: saw the plastic package material vertically downward along the setting direction of the metal beam  2 ′ from the top surface of the entire plastic package  15 ′, and saw to a depth until the upper surface of the lead external portion  122 ′ of the lead frame. In the production process, it is possible to estimate the downward sawing thickness by subtracting the height of the lead frame from the height of the plastic package  15 ′, and the required precision can be obtained in this sawing step by presetting the sawing tool with the sawing thickness.   

     In actual operation of this step, as consistent with implementation example 1′, in order to avoid insufficient saw off of the plastic package material, the estimated sawing thickness can be slightly increased to ensure that the sawing operation can be finished at once, and the surface of the entire metal beam  2 ′ and that of each lead external portion  122 ′ in each lead frame unit, which is connected with the metal beam  2 ′, can be external, thus effectively improving the sawing quality and packaging efficiency. Alternatively the plastic package molding material can be removed by laser blasting or other suitable methods.
     Step 4 Second package sawing: use a thin sawing tool to saw the entire lead frame horizontally and vertically, then separate each lead frame unit  1 ′, forming individual semiconductor plastic package components  3 ′ with external leads (as shown in  FIG. 5F  and  FIG. 6F ); The specific procedure is as follows: Step 4.1. Beam sawing: vertically saw off the metal beam  2 ′ between adjacent plastic package strips  151 ′, separate the connection among the leads  12 ′ of each lead frame unit, and keep the external portion  122 ′ of each lead; Step 4.2. Sawing: horizontally saw through between the lead frame units of plastic package strips  151 ′, and separate to form a plurality of individual semiconductor components  3 ′ with external leads.   

     In another implementation example of this invention, the horizontal sawing can be done before vertical beam sawing in Step 4, i.e.: Step 4.1 Sawing: horizontally saw between the lead frame units of plastic package strips  151 ′ across the metal beams with sections of metal beams connecting a plurality of lead frame units; Step 4.2 Beam sawing: vertically saw off the metal beam  2 ′ sections between adjacent lead frame units, separate the connection among the leads  12 ′ of each lead frame unit, and keep the external portion  122 ′ of each lead, forming a plurality of individual semiconductor components  3 ′ with external leads. 
     The processing moulds and mechanical tools utilized in the process for semiconductor packaging with external leads as provided in this invention are applicable to different lead-exposed semiconductor package types and processes, without additional design and manufacturing of particular operating tools including moulds, thus effectively improving plastic packaging efficiency and reducing manufacturing cost. 
     Although the detailed contents of this invention have been introduced through the above selected implementation examples, it should be noted that the above description shall not be deemed as limitation on this invention. After technical personnel in this field have read the above contents, multiple modifications and substitutions to this invention will be self-evident. Therefore, the protection scope of this invention shall be limited by the attached claims.