Patent Publication Number: US-2020303273-A1

Title: Power module

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2019-052340, filed on Mar. 20, 2019; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments relate to a power module. 
     BACKGROUND 
     Conventionally, a power module that controls a current has been developed, and includes a substrate fixed inside a housing, and power semiconductor elements mounted to the substrate; electrodes of the power semiconductor elements are drawn out of the housing by a metal plate terminal; and a gel material is filled into the housing. It is desirable for such a power module to have high reliability for the thermal load generated when repeatedly conducting/blocking. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a power module according to a first embodiment; 
         FIG. 2  is a perspective cross-sectional view showing the power module according to the first embodiment; 
         FIG. 3  is a cross-sectional view showing the power module according to the first embodiment; 
         FIG. 4A  is a cross-sectional view showing a room-temperature state of a power module according to a comparative example; 
         FIG. 4B  is a cross-sectional view showing a high-temperature state of the power module according to the comparative example; 
         FIG. 4C  is a cross-sectional view showing a high-temperature state of the power module according to the first embodiment; 
         FIG. 5  is a perspective view showing a power module according to a second embodiment; 
         FIG. 6  is a perspective cross-sectional view showing the power module according to the second embodiment; 
         FIG. 7A  is a cross-sectional view showing a room-temperature state of the power module according to the second embodiment; 
         FIG. 7B  is a cross-sectional view showing a high-temperature state of the power module according to the second embodiment; 
         FIG. 8  is a perspective exploded view showing a power module according to a third embodiment; 
         FIG. 9  is a perspective cross-sectional view showing the power module according to the third embodiment; 
         FIG. 10  is a cross-sectional view showing the operation of the power module according to the third embodiment; 
         FIG. 11  is a perspective exploded view showing a power module according to a fourth embodiment; 
         FIG. 12  is a perspective cross-sectional view showing the power module according to the fourth embodiment; 
         FIG. 13A  is a perspective view showing the power module assumed in a first test example; 
         FIG. 13B  shows an analysis model of the gel material; 
         FIG. 13C  shows a strain distribution of the gel material; 
         FIG. 14  is a graph showing the effects of the height of the planar portion  33  on the strain amount of the gel material, in which the horizontal axis is a height h of the planar portion  33  of the metal plate terminal  30 , and the vertical axis is the maximum value of the strain of the gel material; 
         FIG. 15A  shows an analysis model of the gel material in the case where the partition plate is not provided; 
         FIG. 15B  shows an analysis model of the gel material of the case where the partition plate is provided; and 
         FIG. 15C  is a graph showing the effects of the existence or absence of the partition plate on the strain amount of the gel material, in which the horizontal axis is the existence or absence of the partition plate, and the vertical axis is the maximum value of the strain amount of the gel material. 
     
    
    
     DETAILED DESCRIPTION 
     A power module according to an embodiment includes a housing including an external terminal exposed at an outer surface of the housing, a substrate provided inside the housing, a semiconductor element mounted to the substrate, a wire connected to the semiconductor element, a metal plate terminal provided inside the housing, and a gel material provided inside the housing; the metal plate terminal connects the external terminal to an electrode of the semiconductor element; and the gel material covers the wire, the semiconductor element, the substrate, and a portion of the metal plate terminal. The metal plate terminal includes a first portion disposed inside the gel material between the wire and a top plate of the housing, a second portion bent with respect to the first portion and connected to the electrode of the semiconductor element, and a third portion extending from an end portion of the first portion toward the substrate. 
     First Embodiment 
     A first embodiment will now be described. 
       FIG. 1  is a perspective view showing a power module according to the embodiment. 
       FIG. 2  is a perspective cross-sectional view showing the power module according to the embodiment. 
       FIG. 3  is a cross-sectional view showing the power module according to the embodiment. 
     The drawings are schematic; and the components are not illustrated or emphasized as appropriate. This is similar for the other drawings described below as well. For example, in  FIG. 1  and  FIG. 2 , the top plate of the housing is not illustrated for convenience of illustration. 
     As shown in  FIG. 1  to  FIG. 3 , a housing  10  is provided in the power module  1  according to the embodiment. For example, the housing  10  has a substantially rectangular parallelepiped configuration; and the interior is hollow. A bottom plate  11 , a side plate  12 , and a top plate  13  are provided in the housing  10 . For example, the bottom plate  11  and the top plate  13  have rectangular flat plate configurations. For example, the side plate  12  has a quadrilateral tubular configuration. 
     Multiple external terminals  14  are provided at the top plate  13 . The external terminals  14  are exposed at the outer surface of the housing  10 . Through-holes  15  are formed to pierce the top plate  13  and the external terminals  14 . Although the direction from the bottom plate  11  toward the top plate  13  is called “up” and the direction from the top plate  13  toward the bottom plate  11  is called “down” hereinbelow, these expressions are for convenience and are independent of the direction of gravity. “Up” and “down” also are generally referred to as the “vertical direction.” 
     For example, an insulative substrate  20  is provided on the bottom plate  11 . Multiple semiconductor elements  21  are mounted on the upper surface of the substrate  20 . The semiconductor element  21  is, for example, a power semiconductor element, e.g., a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a bipolar transistor, a diode, etc. The major semiconductor material that is used to form the semiconductor element  21  is, for example, silicon carbide (SiC) or silicon (Si). For example, two or three electrodes  22  are provided on each semiconductor element  21 . Wires  23  are connected between the electrodes  22  of the different semiconductor elements  21 . Loops are formed in the wires  23  above the semiconductor elements  21 . 
     For example, three metal plate terminals  30  are provided inside the housing  10 . Only one metal plate terminal  30  is illustrated in  FIG. 1  to  FIG. 3 . The metal plate terminal  30  includes a metal and is made of, for example, copper (Cu). For example, the metal plate terminal  30  is formed by bending one metal plate. 
     Planar portions  31  to  37  are provided as one body in the metal plate terminal  30 . The planar portions  31  to  35  are consecutively arranged in this order. The planar portion  31  is positioned between the side plate  12  and the top plate  13  of the housing  10  and is connected to the external terminals  14  via bolts  16  inserted into the through-holes  15 . In the specification, a “connection” means an electrical connection. 
     The planar portion  32  is bent to extend downward from the end edge of the planar portion  31  inside the housing  10 . The planar portion  33  is bent to extend in a direction (hereinbelow, called the “horizontal direction”) parallel to the upper surface of the substrate  20  from the lower end edge of the planar portion  32 . The planar portion  34  extends downward from the end edge of the planar portion  33  at the side opposite to the boundary between the planar portion  33  and the planar portion  32 . The planar portion  35  is bent to extend in the horizontal direction from the lower end edge of the planar portion  34  and is connected to the electrode  22  of the semiconductor element  21 . Thus, the metal plate terminal  30  connects the external terminals  14  to the electrodes  22  of the semiconductor elements  21 . 
     The planar portion  36  of the metal plate terminal  30  is bent to extend obliquely downward from one of the two end edges of the planar portion  33  other than the end edge continuous with the planar portion  32  and the end edge continuous with the planar portion  34 . The tip of the planar portion  36  is a free end. Similarly, the planar portion  37  is bent to extend obliquely downward from the other of the two end edges described above. The tip of the planar portion  37  is a free end. For example, the planar portions  36  and  37  are tilted to extend away from each other downward. 
     The planar portions  36 ,  33 , and  37  are consecutively arranged in this order. Therefore, the planar portion  32  that extends upward, the planar portion  36  that extends obliquely downward, the planar portion  34  that extends downward, and the planar portion  37  that extends obliquely downward are positioned in four mutually-orthogonal directions when viewed from the planar portion  33  spreading in the horizontal direction. 
     The wires  23  are disposed in the region directly under the planar portion  33 , that is, between the substrate  20  and the planar portion  33 . In other words, the planar portion  33  is disposed between the top plate  13  and the wires  23 . 
     A gel material  40  is sealed inside the housing  10 . The gel material  40  covers the substrate  20 , the semiconductor elements  21 , and the wires  23 . The gel material  40  also covers the lower portion of the planar portion  32  of the metal plate terminal  30  and the entirety of each of the planar portions  33  to  37 . The gel material  40  is insulative; and the elastic modulus of the gel material  40  is lower than the elastic modulus of a metal. The gel material  40  is made of, for example, a silicone gel. The breakage of the wires  23  due to thermal stress can be suppressed by the gel material  40 . Also, the insulative properties between the metal plate terminals  30 , between the wires  23 , between the metal plate terminal  30  and the wires  23 , etc., can be ensured by the gel material  40 . Also, the substrate  20 , the semiconductor elements  21 , the wires  23 , etc., are protected by the gel material  40  from oxygen, moisture, fine particles, etc., entering the housing  10  from the outside. 
     The gel material  40  does not fill the entire interior of the housing  10 ; and an air layer  41  exists on the gel material  40  inside the housing  10 . The housing  10  is not in a perfectly airtight state; and the air of the air layer  41  can flow in and out of the housing  10 . The gel material  40  deforms easily, but is a solid formed as one body and does not leak externally through gaps of the housing  10 . 
     An operation of the power module according to the embodiment will now be described. 
       FIG. 4A  is a cross-sectional view showing a room-temperature state of a power module according to a comparative example;  FIG. 4B  is a cross-sectional view showing a high-temperature state of the power module according to the comparative example; and  FIG. 4C  is a cross-sectional view showing a high-temperature state of the power module according to the embodiment. 
     When electrical power is supplied to the power module  1  and the semiconductor elements  21  conduct, the semiconductor elements  21  generate heat; and the temperature of the entire power module  1  rises. Accordingly, each member of the power module  1  undergoes thermal expansion; but the thermal expansion coefficient is different between the members. The thermal expansion coefficient of the gel material  40  is larger than the thermal expansion coefficient of the housing  10  and the thermal expansion coefficient of the metal plate terminal  30 . Therefore, when the temperature of the power module  1  rises, the increase rate of the volume of the gel material  40  becomes larger than the increase rate of the volume of the housing  10 ; and the upper surface of the gel material  40  rises. When the conduction of the power module  1  stops, the temperature of the power module  1  decreases from the high temperature to room temperature. Thereby, the volume of the gel material  40  decreases; and the upper surface of the gel material  40  drops. 
     In the power module  101  according to the comparative example as shown in  FIGS. 4A and 4B , the planar portions  36  and  37  are not provided in the metal plate terminal  30 . Therefore, when the temperature of the power module  101  rises, the gel material  40  moves upward while contacting end portions  33   a  of the planar portion  33  of the metal plate terminal  30 . At this time, a large shear force is applied from the end portions  33   a  of the planar portion  33  to the gel material  40 . When the temperature of the power module  101  decreases, the gel material  40  moves downward while contacting the end portions  33   a  of the planar portion  33  of the metal plate terminal  30 . 
     Thus, as the heating and the cooling of the power module  101  repeats as the power module  101  operates, a shear force is repeatedly applied to the gel material  40 ; and cracks occur in the gel material  40 . As a result, the support effect of the wires  23 , the insulation effect of the metal plate terminals  30  and the wires  23 , and the protection effect from the external environment which are provided by the gel material  40  decrease; the likelihood of dielectric breakdown occurring between the metal plate terminals  30  increases; and the reliability of the power module  101  undesirably decreases. 
     Conversely, in the power module  1  according to the embodiment as shown in  FIG. 4C , the planar portions  36  and  37  are provided in the metal plate terminal  30 . Therefore, when the temperature of the power module  1  changes, the gel material  40  moves vertically while contacting an end portion  36   a  of the planar portion  36  and an end portion  37   a  of the planar portion  37  without contacting the end portions  33   a  of the planar portion  33 . The movement amount of the gel material  40  when heating and cooling is dependent on the position in the vertical direction; and the movement amount is smaller for the gel material  40  positioned lower, that is, proximal to the bottom plate  11 . Also, the end portions  36   a  and  37   a  are positioned lower than the end portions  33   a . Therefore, the movement amount of the gel material  40  moving while contacting the end portions  36   a  and  37   a  in the power module  1  is smaller than the movement amount of the gel material  40  moving while contacting the end portions  33   a  in the power module  101 . 
     Accordingly, compared to the comparative example, the shear force that is applied to the gel material  40  by the metal plate terminal  30  is small in the embodiment. Therefore, in the power module  1 , the occurrence of the cracks in the gel material  40  can be suppressed. As a result, the reliability of the power module  1  according to the embodiment is high. 
     By disposing the planar portion  33  at a constant height in the power module  1  according to the embodiment, a space for forming the loops of the wires  23  can be ensured between the substrate  20  and the planar portion  33 . Therefore, contacting and shorting of the wires  23  to the planar portion  33  can be prevented. 
     Second Embodiment 
     A second embodiment will now be described. 
       FIG. 5  is a perspective view showing a power module according to the embodiment. 
       FIG. 6  is a perspective cross-sectional view showing the power module according to the embodiment. 
     As shown in  FIG. 5  and  FIG. 6 , the power module  2  according to the embodiment differs from the power module  1  according to the first embodiment (referring to  FIG. 1  to  FIG. 3 ) in that the planar portions  36  and  37  are not provided in the metal plate terminal  30 ; and a low-rigidity plate  51  is provided on the planar portion  33  of the metal plate terminal  30 . 
     The rigidity of the low-rigidity plate  51  is lower than the rigidity of the planar portion  33  of the metal plate terminal  30 . For example, the Young&#39;s modulus of the material of the low-rigidity plate  51  is lower than the Young&#39;s modulus of the material of the metal plate terminal  30 . The low-rigidity plate  51  is made of, for example, a resin material and is made of, for example, PET (PolyEthylene Terephthalate). 
     For example, the low-rigidity plate  51  is bonded to the upper surface of the planar portion  33  of the metal plate terminal  30  by bonding, fastening by bolts, etc. When viewed from above, the low-rigidity plate  51  is larger than the planar portion  33 ; and end portions  51   a  of the low-rigidity plate  51  jut from the end portions  33   a  of the planar portion  33 . 
     An operation of the power module according to the embodiment will now be described. 
       FIG. 7A  is a cross-sectional view showing a room-temperature state of the power module according to the embodiment; and  FIG. 7B  is a cross-sectional view showing a high-temperature state of the power module according to the embodiment. 
     As described above, when viewed from above in the power module  2 , the end portions  51   a  of the low-rigidity plate  51  jut from the end portions  33   a  of the planar portion  33 . Therefore, when the gel material  40  moves vertically due to the thermal cycles, the gel material  40  moves to flow around the end portions  51   a  of the low-rigidity plate  51  without flowing around the end portions  33   a  of the planar portion  33 . 
     As shown in  FIGS. 7A and 7B , because the rigidity of the low-rigidity plate  51  is lower than that of the planar portion  33  of the metal plate terminal  30 , the low-rigidity plate  51  deforms to somewhat follow the movement of the gel material  40 . Thereby, the end portions  51   a  of the low-rigidity plate  51  can relax the shear force applied to the gel material  40 . As a result, the occurrence of the cracks in the gel material  40  can be suppressed. Thereby, the reliability of the power module  2  according to the embodiment is high. 
     The material of the low-rigidity plate  51  may be the same as the material of the metal plate terminal  30 ; and the thickness of the low-rigidity plate  51  may be thinner than the thickness of the planar portion  33  of the metal plate terminal  30 . The rigidity of the low-rigidity plate  51  is caused to be lower than the rigidity of the planar portion  33  thereby; and the effects described above can be obtained. The low-rigidity plate  51  may be bonded to the lower surface of the planar portion  33 . 
     Otherwise, the configuration, the operations, and the effects of the embodiment are similar to those of the first embodiment. 
     Third Embodiment 
     A third embodiment will now be described. 
       FIG. 8  is a perspective exploded view showing a power module according to the embodiment. 
       FIG. 9  is a perspective cross-sectional view showing the power module according to the embodiment. 
     As shown in  FIG. 8  and  FIG. 9 , the power module  3  according to the embodiment differs from the power module  1  according to the first embodiment (referring to  FIG. 1  to  FIG. 3 ) in that the planar portions  36  and  37  are not provided in the metal plate terminal  30 ; and a partition plate  61  is provided to cover the planar portion  33  of the metal plate terminal  30  and the region directly under the planar portion  33 . 
     It is favorable for the partition plate  61  to be made of an insulating material; and the partition plate  61  is made of, for example, a resin material. The partition plate  61  has a configuration in which one rectangular plate is bent into a C-shape. More specifically, vertical portions  63  and  64  that extend downward from two sides of a horizontal portion  62  are provided as one body with the horizontal portion  62  in the partition plate  61 . 
     For example, the horizontal portion  62  is bonded to the upper surface of the planar portion  33  of the metal plate terminal  30  by fixing by a bonding agent, an adhesive sheet, fastening by bolts, etc. When viewed from above, the configuration of the horizontal portion  62  is substantially the same as the configuration of the planar portion  33  or slightly larger. The vertical portions  63  and  64  are bent from the horizontal portion  62  to cover the end portions  33   a  at the two sides of the planar portion  33 . For example, the lower ends of the vertical portions  63  and  64  do not reach the substrate  20 . A space  65  between the planar portion  33  and the substrate  20  is partitioned from the periphery by the planar portions  33  and  34  of the metal plate terminal  30 , the vertical portions  63  and  64  of the partition plate  61 , and a portion of the side plate  12  of the housing  10 . 
     An operation and effects of the power module according to the embodiment will now be described. 
       FIG. 10  is a cross-sectional view showing the operation of the power module according to the embodiment. 
     In the embodiment as shown in  FIG. 10 , the space  65  is partitioned by the planar portions  33  and  34  of the metal plate terminal  30 , the vertical portions  63  and  64  of the partition plate  61 , and a portion of the side plate  12  of the housing  10 . Therefore, a portion  40   a  of the gel material  40  disposed inside the space  65  and portions  40   b  of the gel material  40  disposed outside the space  65  are substantially isolated and move separately due to the thermal cycles. 
     In other words, when the power module  3  is heated, the gel material  40  expands; but the planar portions  33  and  34 , the vertical portions  63  and  64 , and the side plate  12  impede the upward movement of the portion  40   a  of the gel material  40  disposed inside the space  65 . On the other hand, the portions  40   b  of the gel material  40  disposed outside the space  65  move upward along the surfaces of the vertical portions  63  and  64  of the partition plate  61 . At this time, the vertical portions  63  and  64  are substantially not interposed in the movement path of the portions  40   b ; therefore, the vertical portions  63  and  64  substantially do not apply shear forces to the portions  40   b  of the gel material  40 . Therefore, the occurrence of the cracks in the gel material  40  can be suppressed. 
     Because the partition plate  61  is insulative, shorts do not occur even when the partition plate  61  contacts the wires  23  and the electrodes  22  of the semiconductor elements  21 . 
     The horizontal portion  62  of the partition plate  61  may be adhered to the lower surface of the planar portion  33  of the metal plate terminal  30 . 
     Otherwise, the configuration, the operations, and the effects of the embodiment are similar to those of the first embodiment. 
     Fourth Embodiment 
     A fourth embodiment will now be described. 
       FIG. 11  is a perspective exploded view showing a power module according to the embodiment. 
       FIG. 12  is a perspective cross-sectional view showing the power module according to the embodiment. 
     As shown in  FIG. 11  and  FIG. 12 , the power module  4  according to the embodiment differs from the power module  3  according to the third embodiment (referring to  FIG. 8  to  FIG. 10 ) in that a partition plate  66  is provided instead of the partition plate  61 . 
     Similarly to the partition plate  61 , it is favorable for the partition plate  66  to be made of an insulating material; and the partition plate  66  is made of, for example, a resin material. Although the partition plate  66  also has a configuration in which one rectangular plate is bent into a C-shape, the direction of the bend is different from that of the partition plate  61 . Vertical portions  67 ,  68 , and  69  are provided as one body in the partition plate  66 . 
     For example, the vertical portion  67  of the partition plate  66  is bonded to the surface of the planar portion  34  of the metal plate terminal  30  at the side opposite to the planar portion  33  by being fixed by a bonding agent, an adhesive sheet, fastening by bolts, etc. For example, the lower end of the vertical portion  67  does not reach the substrate  20 . The vertical portions  68  and  69  are bent from the two horizontal-direction end portions of the vertical portion  67  toward the planar portion  32 . A space that corresponds to the region directly under the planar portion  33  of the metal plate terminal  30 , i.e., the space  65  between the planar portion  33  and the substrate  20 , is partitioned from the periphery by the planar portions  33  and  34  of the metal plate terminal  30 , the vertical portions  68  and  69  of the partition plate  66 , and a portion of the side plate  12  of the housing  10 . 
     The vertical portion  67  of the partition plate  66  may be bonded to the surface of the planar portion  34  of the metal plate terminal  30  at the planar portion  33  side. 
     Otherwise, the configuration, the operations, and the effects of the embodiment are similar to those of the third embodiment. 
     First Test Example 
     A first test example will now be described. 
     In the test example, the effects of the height of the planar portion  33  of the metal plate terminal  30 , i.e., the distance from the bottom plate  11 , on the strain of the gel material  40  were verified. 
       FIG. 13A  is a perspective view showing the power module assumed in the test example;  FIG. 13B  shows the analysis model of the gel material; and  FIG. 13C  shows the strain distribution of the gel material. The portion shown in  FIG. 13C  corresponds to an A-A′ cross section of  FIG. 13B . 
       FIG. 14  is a graph showing the effects of the height of the planar portion  33  on the strain amount of the gel material  40 , in which the horizontal axis is a height h of the planar portion  33  of the metal plate terminal  30 , and the vertical axis is the maximum value of the strain of the gel material. 
     As shown in  FIG. 13A , the configuration of the power module assumed in the test example is the same as the configuration of the power module  101  according to the comparative example shown in  FIG. 4A  in which the planar portions  36  and  37  of the metal plate terminal  30  are excluded from the power module  1  according to the first embodiment. 
     The strain that is generated in each portion of the gel material  40  for the power module  101  shown in  FIG. 13A  was simulated for when the gel material  40  undergoes thermal expansion as shown in  FIG. 13B . As a result, as shown in  FIG. 13C , the strain of the gel material  40  had a maximum at the end portion vicinity of the planar portion  33 . 
     Such a simulation was performed multiple times for different heights of the planar portion  33 . As shown in  FIG. 14 , the maximum value of the strain amount decreased as the height of the planar portion  33  was reduced. Therefore, it was confirmed that the strain amount of the gel material  40  can be reduced by providing the planar portions  36  and  37  in the metal plate terminal  30  and by lowering the positions of the end portion  36   a  of the planar portion  36  and the end portion  37   a  of the planar portion  37  as in the first embodiment. It is considered that the likelihood of cracks occurring in the gel material  40  is reduced by reducing the strain amount of the gel material  40 . 
     Second Test Example 
     A second test example will now be described. 
     In the test example, the effects of the existence of the partition plate in the third and fourth embodiments on the strain of the gel material was verified. 
       FIG. 15A  shows an analysis model of the gel material in the case where the partition plate is not provided;  FIG. 15B  shows the analysis model of the gel material of the case where the partition plate is provided; and  FIG. 15C  is a graph showing the effects of the existence or absence of the partition plate on the strain amount of the gel material, in which the horizontal axis is the existence or absence of the partition plate, and the vertical axis is the maximum value of the strain amount of the gel material. 
     The model shown in  FIG. 15A  assumes the power module  101  according to the comparative example described above. The model shown in  FIG. 15B  assumes the power module  3  according to the third embodiment and the power module  4  according to the fourth embodiment described above. 
     As shown in  FIGS. 15A and 15B , the distribution of the strain generated in the gel material  40  when the gel material  40  undergoes thermal expansion was simulated for the cases with and without the partition plate. As a result, as shown in  FIG. 15C , the maximum value of the strain amount of the gel material  40  was lower for the case where the partition plate is provided than for the case where the partition plate is not provided. It is therefore considered that compared to the power module  101  according to the comparative example, in the power module  3  according to the third embodiment and the power module  4  according to the fourth embodiment, the strain amount of the gel material  40  is low; and the likelihood of cracks occurring in the gel material  40  is low. 
     According to the embodiments described above, a power module that has high reliability can be realized. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.