Patent Publication Number: US-2019189544-A1

Title: Semiconductor package and method of manufacture

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims foreign priority to European Patent Application No. 17209013.6 filed on Dec. 20, 2017, the entirety of which is incorporated by reference hereby. 
    
    
     FIELD 
     The present disclosure relates to a leadframe for a semiconductor package. In particular the present disclosure relates to a clip based package. 
     BACKGROUND 
     Semiconductor packages use so-called clips to provide electrical external connections to terminals on the semiconductor die. Clip based packages typically have improved electrical, mechanical and thermal performance when compared with packages using wire based, so-called wire bond, connections. 
     Whilst clip based packages have improved reliability and performance when compared to wire bond arrangements, they can suffer from issues related to consistent manufacturability. For example, at one end the clips are typically attached to the terminals of the semiconductor packages using a solder material. At an opposite end the clips may also be attached to the external lead using a solder material. A process known as reflow is then use to form the connections of the clip to the terminals of the semiconductor packages and to the external lead. However, effects such as out-gassing can cause the clip to move relative to the terminals of the semiconductor package and and/or the external lead which result in tilting or rotation of the clip. Tilting or rotation of the clip may result in long-term package reliability or a complete failure of the package. In particular, tilting of the clip also known as tomb-stoning, that is movement of the clip upwards such that end of the clip is raised with respect to the terminal of the semiconductor die may be caused by the surface tension of the solder pulling the clip upwards. 
     SUMMARY 
     According to an embodiment there is provided a semiconductor package, comprising: a leadframe having a die attach portion and a lead portion; a semiconductor die mounted on the die attach portion, the semiconductor die having a contact terminal arranged thereon; a clip portion having: a first tab portion receivably mounted in a hole in the lead portion, and a second tab portion arranged on either side of the first tab portion, wherein the second tab portions are fixedly mounted to connect the clip portion to the lead portion. 
     The first tab portion may be angled with respect to the lead portion such that the first tab portion is received by the hole in the lead portion. The length of the first tab portion may be equal to or longer than the thickness of the lead portion. The first tab portion is angled with respect to the lead portion by approximately 90 degrees. The second tab portions may be substantially parallel to the lead portion and the angled with respect the first tab portion by approximately 90 degrees. 
     The clip portion may be further mounted to the contact terminal of the semiconductor die. The clip portion may further comprise one or more holes adjacent to the first tab portion configured and arranged to allow for venting of gasses. The tab portion may be tapered such that it is thicker at an end proximal the clip portion and thinner at an end distal the clip portion. 
     According to an embodiment there is also provided method of manufacturing a semiconductor package, the method comprising: providing a leadframe having a die attach portion and a lead portion; mounting a semiconductor die on the die attach portion, the semiconductor die having a contact terminal arranged thereon; providing a clip portion having a first tab portion and a second tab portion arranged on either side of the first tab portion, receivably mounting the first tab portion in a hole in the lead portion and fixedly mounting the second tab portions to the lead portion. 
     The first tab portion may be angled with respect to the lead portion and the hole in the lead portion receives the first tab portion. The first tab portion may extend through the hole. The first tab portion may be angled with respect to the lead portion by approximately 90 degrees. 
     The second tab portions may be arranged substantially parallel to the lead portion and angled with respect the first tab portion by approximately 90 degrees. The clip portion may be mounted to the contact terminal of the semiconductor die. The method may further comprise providing one or more holes in the clip portion adjacent to the first tab portion configured and arranged to allow for venting of gasses. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features of the present disclosure can be understood in detail, a more particular description is made with reference to embodiments, some of which are illustrated in the appended figures. It is to be noted, however, that the appended figures illustrate only typical embodiments and are therefore not to be considered limiting of its scope. The figures are for facilitating an understanding of the disclosure and thus are not necessarily drawn to scale. Advantages of the subject matter claimed will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying figures, in which like reference numerals have been used to designate like elements, and in which: 
         FIG. 1 a    illustrates a plan view of a semiconductor device, without moulding, according to an embodiment; 
         FIG. 1 b    illustrates a side view of the semiconductor device, without moulding, according to an embodiment; and 
         FIGS. 2 a  to 2 f    illustrates process steps for manufacturing the semiconductor device in accordance with embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1 a    illustrates a plan view of a semiconductor package  100  according to an embodiment. For the purposes of clarity and explanation a moulding compound or material is not illustrated, however the skilled person will appreciate that this may be formed in any appropriate manner as illustrated for example in  FIG. 2   f.    
     In overview, the semiconductor device comprises one or more semiconductor dies  102  mounted on a respective die attach portion  104  of a lead frame. A clip portion  108 , electrically connects a contact terminal of the semiconductor die  102  to a lead portion  106  of the lead frame. The clip portion  108  includes a first tab portion  110  which is configured and arranged to be engageably received by, or mate with, a corresponding a hole  112  in the lead portion  106 . The clip portion  108  further includes second tab portions  114  arranged on either side of the first tab portion  110 . The second tab portions  114  are substantially parallel to a top surface of the lead portion  106 . 
     The first tab portion  110  may form a clearance fit with the corresponding hole  112  in the lead portion  106 , such that the first tab portion  110  is slideably received by the hole  112 . As discussed below, this allows the clip portion  108  to moved up or down during the reflow process, but prevents the clip portion  108  from rotating with respect to the lead portion  106  and/or the contact terminals of the semiconductor die  102 . In other words, the arrangement of the first tab portion  110  with side walls of the corresponding hole  112  limits or restricts the movement of the clip portion  108  parallel to the surface of the contact terminals of the semiconductor die  102 . In addition, the length of the first tab portion  110  may be such that it protrudes through the lead portion, or in other words, the length of the first tab portion  110  may be longer than the thickness of the lead portion  106  in which the hole  112  is formed, this prevents disengagement of the first tab portion  110 , and thus the clip portion  108 , from the lead frame  106 . 
     Optionally, the first tab portion  110  may form a location-transition fit or an interference fit with the side walls of the hole  112 . 
     One or more outgassing holes  116  may also be provided in the clip portion  108 , adjacent to the first tab portion  110  which allow venting of gasses during the solder reflow process, as discussed in more detail below. The outgassing holes  116  allow reflow gasses to be released thereby preventing a build-up of gaseous pressure under the clip portion which may have the effect of forcing the clip portion  108  upwards. 
     A solder material may be provided between the second tab portions  114  and the lead portion  106 . Due to the arrangement of a second tab portions  114  on either side of the first tab portion  110 , any imbalance in forces due to surface tension generated between the solder and the second tab portions  114  will be balanced thus preventing the clip from tilting upwards, that is tomb-stoning, with respect to the contact terminals of the semiconductor die  102 . Furthermore, the second tab portions  114  are arranged to be substantially parallel with respect to an upper surface of the lead portion  106 . This has the effect that any burrs or raised edges which may remain in the second tab portions  114  do not affect the height of the clip portion  108  as it is mounted on the lead portion  106 . In addition, this has the added advantage that a deburring process, that is, the removal of burrs or raised edges is not required. 
       FIG. 1 b    is a side view of the semiconductor device of  FIG. 1   a,  according to an embodiment. As illustrated in  FIG. 1  b the first tab portion  110  extends into and through the hole  112  in the lead portion  106 . The first tab portion  110  may extend through the hole  112  to prevent disengagement of the first tab portion  110 , and thus the clip portion  108 , from the lead frame  106 , as discussed above. 
     The first tab portion  110 , as it extends into or through the hole, is bent or angled with respect to the second tab portions  114 . Preferably, the first tab portion  110  is bent or angled by 90 degrees (±5 degrees), however, optionally, the first tab portion  110  may bent or angled such that it is received by the hole  112  in the lead portion  106 . 
     The end of the first tab portion  110 , that is the end which is arranged to be inserted into the hole  112  in the lead portion  106  may be tapered. This allows for easier insertion of the clip portion  108  into the lead portion  106  during assembly. 
       FIGS. 2 a  to 2 f    illustrate the various process steps in manufacturing the semiconductor device  100  in accordance with an embodiment. 
     Starting with  FIG. 2   a,  a lead frame comprising a die attach portion  104  and a plurality of lead portions  106  is provided. The die attach portion  104  and lead portions  106  may be formed of any appropriate material such as copper. In addition, each of the lead portions comprise at least one hole or slot  112 , which as discussed above is arranged receive the first tab portion  110  of the clip portion  108 . 
     In the next step as illustrated in  FIG. 2 b    a die attach material  204  is dispensed onto the die attach portion  104 . The die attach material  204  is arranged for fixedly mounting the semiconductor die  102  to the die attach portion  104 . The die attach material may be any appropriate adhesive material such as a solder or conductive adhesive. In addition, a clip portion attachment material  206  may be dispensed onto the lead portion  106 . The clip portion attachment material  206  may be arranged to fixedly mount the clip portion  108  to the lead portion  106 . Specifically, the clip attach material  206  is arranged on the lead portion such that it fixedly contacts the second tab portions  114  arranged on either side of the first tab portion  110 . The clip attach material  206  may be a solder material as discussed above. 
     Dispensing of the die attach material  204  may optionally be carried out simultaneously with the dispensing of the clip attach material  206 . Optionally the die attach material  204  may be formed of the same material as the clip attach material  206 . 
     Following dispensing of the die attach material  204  and the clip attach material  206 , the semiconductor die  102  is attached to the die attach portion  104  of the lead frame as shown in  FIG. 2   c.  Following placement of the semiconductor die  102 , a contact terminal attach material  208  is dispended on the contact terminals of the semiconductor die  102  for electrical and mechanical connection of the clip portion  106  to the semiconductor die  102 . The die attach material  204  may be applied by any appropriate process such as solder printing or solder dispense. 
     Once the semiconductor die  102  is in place on the die attach portion  104 , the contact terminal attach material  208  is arranged on the contact terminals of the semiconductor die as illustrated in  FIG. 2   d.  The clip portion  108  may then be arranged on the contact terminals and on the lead portion  106  as illustrated in  FIG. 2   e.    
     The first tab portion  110  of the clip portion  108  is inserted into the hole  112  of the lead portion  106  and this aligns the clip portion  108  with the contact terminals of the semiconductor die  102  and also aligns the second tab portions  114  the lead portion  106  and thus with the clip attach material  206  arranged on the lead portion  106 . This arrangement results in the second tab portions  114  which are parallel or substantially parallel with the top surface of the lead portion  106  and the weight of the clip portion  108  together with the amount of solder dispensed on the lead portion  106  ensures that the thickness of the solder connecting the second tab portions  114  to the lead portion  106  will also be uniform. Typically, the solder thickness will be uniform and in the region of 1 μm to 5 μm. The specific solder thickness will be dependent on the volume of the solder dispensed. 
     Following the attachment of the clip portion  108  to the contact portion of the semiconductor die  102  and the lead portion  106 , the assembly undergo goes solder re-flow to solidify the clip attach material  206 , the contact terminal attach material  208  and the die attach material  204 . Following reflow, second tab portions  114  are substantially parallel to a top surface of the lead portion  106 . Gasses generated between the clip portion and the lead portion during the reflow process may be vented by one or more outgassing holes  116  provided in the clip portion. 
     Following reflow, the assembly may be packaged in a mould material as illustrated  FIG. 2   f.    
     Whilst the above embodiments illustrate a so-called dual die arrangement, comprising two semiconductor dies  102 , with two corresponding die attach portions  104  and a plurality of lead portions  106 , the skilled person will appreciate that present disclosure may also relate to single or multi die arrangements as required by the specific functionality of the semiconductor device. As such, embodiments may therefore include at least one semiconductor die  102 , at least one die attach portion  104  and at least one lead portion  106 . 
     Particular and preferred aspects of the present disclosure are set out in the accompanying independent claims. Combinations of features from the dependent and/or independent claims may be combined as appropriate and not merely as set out in the claims. 
     The scope of the present disclosure includes any novel feature or combination of features disclosed therein either explicitly or implicitly or any generalisation thereof irrespective of whether or not it relates to the claimed invention or mitigate against any or all of the problems addressed by the present invention. The applicant hereby gives notice that new claims may be formulated to such features during prosecution of this application or of any such further application derived there from. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in specific combinations enumerated in the claims. 
     Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination. 
     Term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality. Reference signs in the claims shall not be construed as limiting the scope of the claims.