Semiconductor device resistant to thermal cracking and manufacturing method thereof

1. A semiconductor device comprising:

a heat spreader formed in a plate shape;

a semiconductor element formed in a plate shape and joined, to a one-side surface of the heat spreader, at an other-side surface of the semiconductor element via a first joining member;

a first lead frame joined, at an other-side surface thereof, to the one-side surface of the heat spreader via a second joining member;

a second lead frame joined, at an other-side surface thereof, to a one-side surface of the semiconductor element via a third joining member; and

a mold resin sealing the heat spreader, the semiconductor element, the first lead frame, and the second lead frame such that a portion of the first lead frame and a portion of the second lead frame are exposed to outside, wherein

a boundary between the third joining member and the mold resin is present in a gap between the one-side surface of the semiconductor element and the other-side surface of the second lead frame, and

in a cross-sectional shape obtained by cutting a portion around the boundary at a plane perpendicular to the one-side surface of the heat spreader, an angle on the third joining member side out of two angles formed by the one-side surface of the semiconductor element and a straight line connecting an end point of a joining surface between the third joining member and the semiconductor element and an end point of a joining surface between the third joining member and the second lead frame, is not smaller than 90° and not larger than 135°.

2. The semiconductor device according to claim 1 , wherein a protruding portion protruding toward the semiconductor element is formed at a portion of the other-side surface of the second lead frame that is located inward of the portion around the boundary.

3. The semiconductor device of claim 1 , wherein the angle which is not smaller than 90° and is not larger than 135° is about 90°.

4. The semiconductor device of claim 2 , wherein the protruding portion is a parallelepiped, and the third joining member extends beyond an endpoint of the protruding portion in a direction toward a maximum stress generation portion of the semiconductor element.

5. A semiconductor device manufacturing method comprising:

a first step of joining, to a one-side surface of a heat spreader formed in a plate shape, an other-side surface of a semiconductor element formed in a plate shape, the joining being performed via a first joining member;

a second step of joining an other-side surface of a first lead frame to the one-side surface of the heat spreader via a second joining member;

a third step of interposing a third joining member formed of a solid having a fixed thickness between an other-side surface of a second lead frame and a one-side surface of the semiconductor element, then

melting the third joining member by reflow heating, and then

cooling the third joining member, to join the other-side surface of the second lead frame to the one-side surface of the semiconductor element via the third joining member,

the melting and the subsequent cooling of the third joining member being performed such that in a cross-sectional shape obtained by cutting, at a plane perpendicular to the one-side surface of the heat spreader, a portion around a boundary that is between the third joining member and an outer side of the third joining member and that is present in a gap between the one-side surface of the semiconductor element and the other-side surface of the second lead frame, an angle on the third joining member side out of two angles formed by the one-side surface of the semiconductor element and a straight line connecting an end point of a joining surface between the third joining member and the semiconductor element and an end point of a joining surface between the third joining member and the second lead frame, is set to be not smaller than 90° and not larger than 135°; and

a fourth step of sealing the heat spreader, the semiconductor element, the first lead frame, and the second lead frame by a mold resin such that a portion of the first lead frame and a portion of the second lead frame are exposed to outside.

6. The semiconductor device manufacturing method according to claim 5 , wherein a protruding portion formed, so as to protrude toward the semiconductor element, at a portion of the other-side surface of the second lead frame that is located inward of the portion around the boundary presses the third joining member contiguous to the protruding portion at a time of the reflow heating so that a portion of the third joining member that has been squeezed out by the pressing flows toward the end point of the joining surface between the third joining member and the second lead frame at the portion around the boundary, whereby the angle on the third joining member side is set to be not smaller than 90° and not larger than 135°.

7. The semiconductor device manufacturing method according to claim 5 , wherein

the second joining member and the third joining member are joining members formed of a same type of, or a same, material, and

the second step and the third step are performed in a single step.

8. The semiconductor device manufacturing method according to claim 6 , wherein

the second joining member and the third joining member are joining members formed of a same type of, or a same, material, and

the second step and the third step are performed in a single step.

9. The semiconductor device manufacturing method according to claim 5 , wherein

the first joining member, the second joining member, and the third joining member are joining members formed of a same material, and

the first step, the second step, and the third step are performed in a single step.

10. The semiconductor device manufacturing method according to claim 6 , wherein

the first joining member, the second joining member, and the third joining member are joining members formed of a same material, and

the first step, the second step, and the third step are performed in a single step.