Patent Publication Number: US-2019189860-A1

Title: Electronic circuit package cover

Description:
BACKGROUND 
     Technical Field 
     The present disclosure generally relates to the field of electronic circuits, and more particularly to covers and methods for forming of covers for integrated circuit packages. 
     Description of the Related Art 
     Certain electronic packages comprise an electronic chip housed in a package. Such a package often comprises a support portion having the chip affixed thereto, and a cover portion covering the chip. 
     When the electronic circuit is an optical signal transmit and/or receive circuit, such as a time-of-flight measurement proximity sensor, the electronic chip comprises optical signal transmit and receive regions. The cover then comprises, opposite the transmit/receive regions, elements transparent for the wavelengths of the optical signals, for example, made of glass, such as lenses. 
     Similarly, in various other types of electronic circuits, elements are positioned in the cover. 
     BRIEF SUMMARY 
     One embodiment is directed to an electronic circuit, comprising a cover having an element extending therethrough and having a planar main inner surface. 
     According to an embodiment, said element is transparent, filtering, or comprises a lens. 
     According to an embodiment, the cover has a constant thickness. 
     According to an embodiment, said element has the same thickness as the cover. 
     According to an embodiment, the circuit comprises a support supporting a chip. 
     According to an embodiment, the circuit comprises a spacer between peripheral portions of the cover and of the support. 
     According to an embodiment, the spacer is attached to the cover by glue. 
     According to an embodiment, the spacer comprises a housing containing the glue. 
     An embodiment provides an optical transmission and/or reception circuit such as hereabove. 
     According to an embodiment, the optical transmission and/or reception circuit comprises an opaque partition of separation between optical transmission and/or reception regions of the circuit. 
     According to an embodiment, the spacer and the partition form a monoblock assembly. 
     According to an embodiment, the opaque partition is formed of a stack of beads of glue. 
     An embodiment provides a method of manufacturing a circuit such as hereabove. 
     According to an embodiment, the method comprises a step a) of manufacturing the cover by molding. 
     According to an embodiment, the molding is assisted by a film. 
     According to an embodiment, the method comprises, before step a), arranging said element on an adhesive film. 
     According to an embodiment, the method comprises a step b) of positioning the cover with respect to a chip of the circuit. 
     According to an embodiment, said element is transparent or filtering and is positioned at step b) relative to a guide mark on the chip by observing the guide mark through said element. 
     The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a simplified cross-section view of an embodiment of an electronic circuit; 
         FIGS. 2A to 2D  are simplified cross-section views illustrating an embodiment of a method of forming an electronic circuit cover; 
         FIGS. 3A and 3B  are simplified views, respectively in cross-section and in top view, illustrating an embodiment of a sub-assembly of an electronic circuit package; 
         FIGS. 4A to 4C  are simplified cross-section views illustrating an implementation mode of an electronic circuit forming method; 
         FIG. 5  is a partial simplified cross-section view of an alternative embodiment of the sub-assembly of  FIGS. 3A and 3B ; 
         FIGS. 6A and 6B  are respective simplified cross-section and top views illustrating an embodiment of a sub-assembly of an electronic circuit package; and 
         FIGS. 7A and 7B  are simplified cross-section views illustrating an implementation mode of an electronic circuit forming method. 
     
    
    
     DETAILED DESCRIPTION 
     The same elements have been designated with the same reference numerals in the various drawings and, further, the various drawings are not to scale. For clarity, only those steps and elements which are useful to the understanding of the described embodiments have been shown and are detailed. In particular, the electronic chip and the package elements other than the cover are not detailed, the described embodiments being compatible with most current electronic packages and chips. 
     In the following description, when reference is made to terms qualifying absolute positions, such as terms “front,” “rear,” “top,” “bottom,” “left,” “right,” etc., or relative positions, such as terms “above,” “under,” “upper,” “lower,” etc., or to terms qualifying directions, such as terms “horizontal,” “vertical,” etc., it is referred to the orientation of the drawings, it being understood that, in practice, the described devices may be oriented differently. Unless otherwise specified, expressions “approximately,” “substantially,” and “in the order of” mean to within 10%, preferably to within 5%. 
       FIG. 1  is a cross-section view of an embodiment of an electronic circuit  100 . Electronic circuit  100  comprises an electronic chip  102  housed in a package  104 . The electronic chip  102  includes semiconductor material with one or more integrated circuits as is well known in the art. 
     Package  104  comprises a support  110  and a cover  115 . Chip  102  is arranged on a central portion of support  110 , in a closed space particularly delimited by support  110  and cover  115 . 
     As an example, chip  102  comprises an optical transmission region  120  and an optical reception region  122 . Optical transmission/reception regions  120  and  122  are for example separated by an opaque partition  124 . Partition  124  thus separates the closed spaces or cavities delimited by the support and the cover into a transmit area  126  and a receive area  128 . Optical transmission/reception regions  120  and  122  face transparent elements  130  extending through cover  115 . 
     More generally, according to the type of electronic circuit, one or a plurality of elements of any type may be provided instead of the two transparent elements  130  of this example. 
     The main inner surface of cover  115 , facing chip  102  and occupying the inner side of the cover, is planar. A planar surface here designates a surface which does not deviate by more than 10 μm, preferably 5μm, from a plane, over more than 90%, for example, more than 95%, of the inner side of the cover, preferably over the entire inner side of the cover. In particular, the planar surface does not have raised areas higher than 10 μm, preferably no raised areas higher than 5 μm. The planar surface is for example parallel to the main plane of the chip. 
     A spacer, for example, a frame  140 , between peripheral portions  142  and  144  of support  110  and cover  115 , mechanically connects the cover to the support. Frame  140  is for example thicker than chip  102 , and chip  102  is thus located under the level of cover  115 . Frame  140  is typically glued (glues  146  and  148 ) to the respective peripheral portions  142  and  144  of support  110  and of cover  115 . As a variation, the spacer may be a portion of support  110 , for example corresponding to raised peripheral portions of support  110 . 
     The fact of providing a planar surface provides an accurate positioning of elements  130  in the cover, which enables to avoid, in the electronic circuit, problems of misalignment between chip  102  and elements  130 . 
     As an example, cover  115  has the shape of a plate of constant thickness. The cover is here considered as having a constant thickness if it does not have, over for example more than 90%, for example, more than 95% of its surface, preferably over its entire surface, a thickness variation of more than for example 10%, preferably 5%. The thickness of elements  130  is for example in the range from 100 μm to 400 μm. As an example, cover  115  and elements  130  have a same constant thickness. 
       FIGS. 2A to 2D  are simplified cross-section views illustrating an embodiment of a method of forming a cover  115  having elements  130  extending therethrough. 
     As an example, a plurality of covers  115  arranged in an array are simultaneously manufactured, and  FIGS. 2A to 2D  illustrate the manufacturing of two neighboring covers. 
     At the step of  FIG. 2A , elements  130 , for example, having a same thickness, are positioned on a planar surface of an adhesive support, for example, a first adhesive film  200 . Adhesive film  200  is provided to maintain elements  130  in place in the rest of the process, and to be removed afterwards. As an example, adhesive film  200  is a polymer film, having a thickness for example in the range from 10 to 100 μm, covered with a layer of an adhesive allowing a temporary mechanical bonding. As an example, adhesives known under trade names “Lintec C-902” or “Nitto Revalpha” may be used. 
     At the step of  FIG. 2B , elements  130  are covered with a second film  210 . Film  210  rests on the upper surfaces of elements  130 . Film  210  is not in contact with adhesive film  200  between elements  130 . Film  210  for example remains parallel to the upper surface of adhesive film  200 . 
     At the step of  FIG. 2C , the entire structure obtained at the step of  FIG. 2B  is placed in a mold. Adhesive film  200  and film  210  are against inner surfaces of the mold, not shown, which are, for example, planar and parallel. A layer  115 A, for example, of constant thickness, is formed by molding between the films. During the molding, the films rest on the surfaces of the mold. As an example, layer  115 A is made of a thermosetting polymer. 
     At the step of  FIG. 2D , adhesive film  200  and film  210  are removed, after which layer  115 A is divided into individual covers  115 , for example, by cutting along lines  220 . In each of the obtained covers  115 , the material of layer  115 A bonds to the sides of elements  130 , which maintains elements  130  in place in the cover. Each of the covers  115  thus obtained has a planar main surface, and preferably its two main surfaces are planar and parallel to each other. 
     The method of  FIGS. 2A to 2D  enables to obtain, in each cover  115 , one or a plurality of accurate distances d 1  between elements  130 , with an accuracy better than for example in the order of 5μm. As an example, distances d 1  are in the range from 0.5 mm to 5 mm. Distances d 1  are accurately obtained despite the fact that, during the molding of the step of  FIG. 2C , displacements of elements  130  may occur, for example, due to deformations of adhesive film  200 . Such displacements particularly occur when layer  115 A corresponds to several hundreds, or even several thousands, of covers  115 . Such displacements affect entire regions of layer  115 A in the same way, and neighboring elements  130  move together. Thereby, the values of distances d 1  in covers  115  are the same as those obtained on installation of elements  130  at step  2 A. As a result, distances d 1  are accurately obtained even if distances d 2  between elements  130  and cutting lines  220  may vary from one cover  115  to the other. 
     Although layer  115 A has been formed by molding assisted by a film  210  at the step of  FIG. 2B , as a variation, film  210  may be omitted. 
       FIGS. 3A and 3B  are simplified cross-section and top views and illustrate an embodiment of a sub-assembly  300  of an electronic circuit package. The cross-section plane of  FIG. 3A  is plane A-A shown in  FIG. 3B . 
     Sub-assembly  300  comprises frame  140  and for example partition  124 . Sub-assembly  300  is for example monoblock. Typically, sub-assembly  300  is formed by molding, for example of a thermosetting polymer, for example, the same polymer as that of layer  115 A of  FIG. 2C . 
     As an example, frame  140  has a planar main surface  302 . Frame  140  may be rectangular, partition  124  connecting two opposite members of the frame. Partition  124  for example has a surface located in the plane of surface  302 . For an optical electronic transmission and/or reception circuit, the material of sub-assembly  300  is preferably opaque to the wavelengths of the signals transmitted and received by the circuit. 
       FIGS. 4A to 4C  are simplified cross-section views of an embodiment of an electronic circuit forming method, for example, from a sub-assembly  300  of the type in  FIGS. 3A and 3B  and a cover  115  of the type obtained by the method of  FIGS. 2A to 2D . 
     At the step of  FIG. 4A , a chip  102 , for example, an optical transmission/reception chip comprising optical transmission and reception regions  120 ,  122 , is arranged on a central portion of a support  110 . Frame  140  of sub-assembly  300  is mechanically bonded, for example, by glue  146 , to peripheral portion  142  of support  110 , so that partition  124  of sub-assembly  300  is located on the chip between regions  120  and  122 . Planar surface  302  of sub-assembly  300  is located on the side opposite to support  110 . 
     At the step of  FIG. 4B , the planar surface of cover  115  is brought towards surface  302  of frame  140 . Cover  115  is positioned relative to chip  102 , for example, by a horizontal displacement  400  taking one of elements  130  to a position adjusted, along an axis  402 , opposite an optical transmission or reception region  120 . Cover  115  may if desired be rotationally adjusted to take another element  130  to a position adjusted along an axis  412 . 
     Due to the fact that distances d 1  between elements are accurate, all elements  130  can thus be accurately positioned. This is possible despite possible variations of distances d 2  between elements  130  and the edges of cover  115 , since the cover can be freely displaced in the horizontal direction. In this example, this possibility of freely displacing the cover in the horizontal direction results from the fact that the main surface of the cover facing the inside of the circuit is planar. Any other shape of the cover capable of enabling to horizontally displace the cover with respect to the support may be provided. 
     As an example, to take an element  130  to an accurate position, a guide mark has been provided on the chip, for example, an edge of an optical transmission component of the chip is used. The position of transparent element  130  is adjusted with respect to the guide mark by observing the guide mark through the transparent element. Any other known method enabling to adjust the position of element  130  may be used for this purpose, for example, by a laser or by optical observation. 
     As a variation, any type of element  130 , specific to an electronic circuit, may be positioned relative to a chip of the electronic circuit positioned on a support  110 , for example, by adjustment of the position of an accessible portion of element  130  relative to a guide mark accessible on support  110 . An optical access to the guide marks may be provided for this purpose. 
     At the step of  FIG. 4C , cover  115  is mechanically bonded to frame  140  of sub-assembly  300 , for example, by glue  148 , in the position obtained at the step of  FIG. 4B . As an example, glue  148  is arranged before the step of  FIG. 4B  and the polymerization of glue  148  is carried out at the step of  FIG. 4C . Partition  124  may be glued to the cover. 
       FIG. 5  is a partial simplified cross-section view of an example of a variation of frame  140  of sub-assembly  300  of  FIGS. 3A and 3B . 
     Frame  140  has, on its surface intended to be glued to cover  115 , a housing  500  intended to receive glue  148 . As an example, housing  500  is a groove extending around surface  302  of the frame between two shoulders  504  and  506 . As a variation, not shown, housing  500  is delimited by a single shoulder and emerges into the outer or inner edge of the frame. Similarly, frame  140  may have, on its surface intended to be glued to support  110 , a housing  510  intended to receive glue  146 . Housing  510  may be a groove or a housing delimited by a shoulder and emerging into the outer or inner edge of the frame. 
       FIGS. 6A and 6B  are simplified cross-section and top views illustrating an embodiment of a frame  140 A of an electronic circuit package. Cross-section plane A-A of  FIG. 6A  is shown in  FIG. 6B . 
     Frame  140 A is identical to frame  140  of sub-assembly  300  of  FIG. 3A , with the difference that frame  140 A does not form a monoblock assembly with partition  124 . In particular, the variation of frame  140  of  FIG. 5  is compatible with frame  140 A. 
       FIGS. 7A and 7B  are simplified cross-section views illustrating an embodiment of a method of forming an electronic circuit, for example, from the frame of  FIGS. 6A and 6B  and covers  115  of the type obtained by the method of  FIGS. 2A to 2D . The step of  FIG. 7A  corresponds to that of  FIG. 4A , where, instead of partition  124 , a bead of glue or a stack of beads of glue  124 A is formed between transmission/reception regions  120  and  122  of the chip. As an example, each bead of glue  124 A has a thickness in the range from 200 μm to 1 mm. As an example, the stack comprises 4 or more beads. Beads  124 A are for example made of glue such as that known under trade name “Delo GE7985,” or of any other material intended to harden, for example, by polymerization, suitable to form a bead or stacked beads, preferably opaque after hardening. 
     At the step of  FIG. 7B , steps similar to those of  FIGS. 4B and 4C  are successively implemented. A total thickness of the stack of beads  124 A sufficient for cover  115  to press on the top of the stack on installation of the cover has been provided. The stack deforms. After the installation of the cover, the hardening of the bead material provides an opaque partition. 
     In the obtained electronic circuit, the opaque partition is thus formed of the stack of beads  124 A. As a variation of the method of  FIGS. 7A and 7B , the partition may be formed by any other adapted means. 
     Specific embodiments have been described. Various alterations, modifications, and improvements will occur to those skilled in the art. In particular, although examples applied to transparent elements  130  have been described, all the described embodiments more generally apply to any element housed in a cover for which the same problems are posed, particularly elements comprising lenses, for example, for focusing optical signals, or filtering elements enabling to remove all or part of optical radiations having wavelengths different from those of optical signals transmitted or received by the integrated circuit. 
     Finally, the practical implementation of the described embodiments is within the abilities of those skilled in the art based on the functional indications given hereabove. 
     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. 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.