Heat sink, board module, transmission device, and method of manufacturing the heat sink

1. A heat sink comprising:

a base plate; and

at least one fin secured to the base plate; wherein

the base plate has a plurality of first through holes each of which extends in a first direction and a second direction, the first direction being a direction parallel to a surface of the base plate, the second direction being a direction that is parallel to the surface of the base plate and that is perpendicular to the first direction, wherein

each of the at least one fin has at least one projection each of which inserted into a corresponding first through hole among the plurality of first through holes, each of the at least one projection having a first side and a second side each with an end surface, and wherein,

both end surfaces of each of the at least one projection are in contact with inner wall surfaces of the corresponding through hole entirely in a third direction parallel to a thickness direction of the base plate,

the base plate has one or more of second through holes each of which is formed between an adjacent pair of first through holes among the plurality of first through holes, each of the one or more of second through holes being a through hole formed to alleviate a compressive stress from a compressive load applied to the base plate in at least any of the first direction or the second direction.

2. The heat sink according to claim 1 , wherein

the at least one fin includes a plurality of fins, wherein

the plurality of first through holes are arranged in a rectangular array shape in the first direction and the second direction, and wherein

the plurality of fins are arranged in the second direction.

3. The heat sink according to claim 2 , wherein,

when the plurality of first through holes are classified into a first group and a second group, the first group being a group that includes, out of the plurality of through holes, through holes disposed outermost and adjacent to one another in the first direction or the second direction, the second group being a group that includes, out of the plurality of through holes, through holes disposed in a central portion and adjacent to one another in the first direction or the second direction,

in the second direction, a mass of the base plate per unit area of the surface of the base plate is smaller in a portion between the through holes included in the second group than in a portion between the through holes included in the first group.

4. The heat sink according to claim 2 , wherein

each of the one or more second through holes being a second through hole having a smaller opening area than an opening area of each of the plurality of first through holes is formed on an inner side of a rectangular array formed by four of the plurality of first through holes of the base plate.

5. A board module comprising:

a board;

a heat-generating component provided over the board; and

the heat sink according to of claim 1 provided over the heat-generating component.

6. A transmission device comprising:

the board module according to claim 5 ; and

a housing that houses the board module.

7. A method of manufacturing a heat sink, the method comprising:

preparing a base plate having a plurality of first through holes each of which extends in a first direction and a second direction, the first direction being a direction parallel to a surface of the base plate, the second direction being a direction that is parallel to the surface of the base plate and that is perpendicular to the first direction;

preparing at least one fin, each of the at least one fin having at least one projection each of which inserted into a corresponding first through hole among the plurality of first through holes, each of the at least one projection having a first side and a second side each with an end surface;

performing temporary assembly of the at least one fin and the base plate with each other by inserting each of the at least one projection into the corresponding first through hole from among the plurality of first through holes; and

bringing both end surfaces of each of the at least one projection into contact with inner wall surfaces of the corresponding first through hole entirely in a third direction parallel to a thickness direction of the base plate by compressing the base plate in a second direction that is parallel to the surface of the base plate and that is perpendicular to the first direction, wherein the base plate has one or more of second through holes each of which is formed between an adjacent pair of first through holes among the plurality of first through holes, each of the one or more of second through holes being a through hole formed to alleviate a compressive stress from a compressive load applied to the base plate in at least any of the first direction or the second direction.

8. The method according to claim 7 , wherein

the at least one fin includes a plurality of fins, wherein

the plurality of first through holes are arranged in a rectangular array shape in the first direction and the second direction, and wherein

the plurality of fins are arranged in the second direction.

9. The method according to claim 8 , wherein,

when the plurality of first through holes are classified into a first group and a second group, the first group being a group that includes, out of the plurality of through holes, through holes disposed outermost and adjacent to one another in the first direction or the second direction, the second group being a group that includes, out of the plurality of through holes, through holes disposed in a central portion and adjacent to one another in the first direction or the second direction,

in the second direction, a dimension of the through holes included in the second group is larger than a dimension of the through holes included in the first group.

10. The method according to claim 8 , wherein,

each of the one or more second through holes is a second through hole disposed on an inner side of a rectangular array formed by four of the plurality of first through holes is prepared, and wherein

each of the one or more second through holes has a smaller opening area than an opening area of each of the plurality of first through holes.