JP2003008165A - Semiconductor package mounting structure and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in the prior art that, when a semiconductor package having a side electrode is jointed to a mounting with solder, the solder fillet has an optimul shape in its mountain root, but miniaturization of the package involves unsecured reliability of the shape. SOLUTION: The height (ra) and width (wa) of a package side electrode, and the length (rb) and width (wb) of a mounting part electrode are set to have dimensional mutual relations of ra/rb=0.7 to 1.3 and wa<=wb; and the amount (V) of solder fillet is set to satisfy a relation of (ra×rb×wa÷2)+ ra×rb(wb-wa)÷6<V<π×ra×wa÷4+π×ra×rb(wb-wa)÷12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure of a semiconductor package and a mounting method thereof, and more particularly to an LCC (Leed
less chip carrier) Assembling conditions for soldering a semiconductor package to a mounting board.

[0002]

2. Description of the Related Art FIG. 3 is a view showing a relative arrangement of a semiconductor package having an LCC structure (hereinafter referred to as an LCC package) and electrodes of a substrate to be mounted. FIG. 1A is a perspective view thereof, in which a side surface electrode 2 having a cylindrical concave surface is formed on the side surface of the LCC package 1, and a mounting portion electrode 3 is formed on a substrate to be mounted. FIG. 3B is a Q plane sectional view of the electrode portion.

FIG. 4 is an explanatory view of a conventional example of soldering, FIG. 4A is a perspective view thereof, and FIG. 4B is a sectional view thereof. 4 indicates solder.

In the soldering joining of the LCC package to the mounting substrate, the stress to the joining portion caused by the difference in thermal expansion coefficient between the package and the substrate, the mechanical stress applied to the mounting substrate, etc. are the fillet shape of the solder joining portion. The following two conditions are generally used as the judgment criteria for proper soldering.

(1) As an example of creeping up of solder, in "Introduction to Surface Mount Technology" P226-227 (Kamen Capiro, published by Nihon Almit Co., Ltd.), the creeping up of solder (fillet height) is The pass limit is 50% or more of the height ra of the side surface electrode 2.

(2) Shape of fillet The optimum shape of the solder fillet is the shape of a gentle mountain skirt shown in FIGS. 4 (a) and 4 (b).

[0007]

In recent years, the miniaturization of semiconductor packages has progressed, and the area of the side surface electrodes of the LCC package has also become smaller. In particular, the side surface electrode height ra and the side surface electrode width w.
a is getting smaller. Along with this, the following problems have become prominent.

A major problem in soldering and joining is cracking. Solder cracking occurs in a portion having poor joining strength and generally occurs in a place where the amount of solder is small, an alloy layer, or the like.

Regarding the above-mentioned condition (1) of the prior art,
The reliability of the soldering joint largely depends on the amount of solder and its variation as the height ra of the side surface electrode decreases.

With respect to the condition (2), when ra is low, it is difficult to form a solder mountain skirt-shaped fillet due to the surface tension, and if it is forcibly formed by adjusting the solder temperature, etc. Crawling is low or the amount of solder is small, and as a result the reliability of the solder joint is impaired.

Here, the mechanism of crack generation in the solder joint of the LCC package will be described with reference to FIG. In the figure, S1 to S3 indicate steps of solder crack generation. S1: First, a solder crack occurs on the lower surface of the package. S2: The crack reaches the solder fillet portion on the side surface. S3: Stress concentrates on a thin portion of the solder fillet portion (the distance from the lowermost portion of the side surface electrode to the surface is short), and a crack is generated in the portion.

As described above, the problem of solder cracks becomes more serious with the miniaturization of LCC packages, and the conventional judgment criteria are becoming insufficient.

The present invention solves the above problems and provides a compact LC.
An object of the present invention is to provide a mounting structure and a mounting method for a semiconductor package, which can obtain a highly reliable solder joint even in the case of a C package.

[0014]

In order to achieve the above object, the present invention provides a mounting structure in which a semiconductor package having side electrodes is solder-bonded to a mounting substrate. w a, the length of the mounting portion electrode of the mounting substrate is rb, and the width thereof is w b, the mutual relationship of the electrode dimensions is ra / rb = 0.7 to 1.3, wa
≦ wb, and the joint solder fillet is formed with a solder amount (V) satisfying the following formula. ra ・ rb ・ wa / 2 + ra ・ rb (wb-wa) / 6
<V <π ・ ra ・ rb ・ wa / 4 + π ・ ra ・ rb (w
b-wa) / 12

In a mounting structure in which a semiconductor package having side electrodes is soldered to a mounting substrate, when the height of the side electrodes is ra and the length of the mounting portion electrode of the mounting substrate is rb, The solder fillet is formed such that the distance (L) from the point where the side surface electrode contacts the mounting portion electrode to the solder surface in the solder section cross section satisfies the following formula. ra ・ rb / (ra ² + Rb ² ) ^1/2 <L <(ra ²
+ Rb ² ) ^1/2

Further, in a mounting method of soldering a semiconductor package having a side surface electrode to a mounting board, the height of the side surface electrode is ra, the width is wa, and the length of the mounting portion electrode of the mounting board is rb. When the width is wb, the mutual relation of the electrode dimensions is ra / rb = 0.7 to 1.3,
wa ≦ wb, and the joint solder fillet is formed with a solder amount (V) satisfying the following formula. ra ・ rb ・ wa / 2 + ra ・ rb (wb-wa) / 6
<V <π ・ ra ・ rb ・ wa / 4 + π ・ ra ・ rb (w
b-wa) / 12

In a mounting method of soldering a semiconductor package having a side surface electrode to a mounting board, when the height of the side surface electrode is ra and the length of the mounting portion electrode of the mounting board is rb, soldering is performed. In the partial cross section, the solder fillet is formed so that the distance (L) from the point where the side surface electrode contacts the mounting portion electrode to the solder surface satisfies the following formula. ra ・ rb / (ra ² + Rb ² ) ^1/2 <L <(ra ²
+ Rb ² ) ^1/2

[0018]

1 and 2 are explanatory views of a mounting structure according to the present invention. Each drawing (a) is a perspective view of a mounting portion and each drawing (b) is a sectional view thereof. In the figure, ra and w
a is the height and width of the side surface electrode 2, rb and wb, respectively.
Are the length and width of the mounting portion electrodes, respectively.

In the mounting structure of the present invention, the shape of the solder fillet is not a standard mountain ridge, but the distance (L) from the point where the side surface electrode 2 contacts the mounting portion electrode 3 to the surface of the solder 4 is conventional. Is set longer (in other words, the thickness of the solder from that point is thicker).

FIG. 1 shows an embodiment in which the set value of the distance (L) is the minimum. The solder surface is linearly formed from the upper end of the side surface electrode 2 to the right end of the mounting portion electrode 3,
The distance is given by the following equation. Lmin = ra ・ rb / (ra ² + Rb ² ) ^1/2

FIG. 1 also shows an embodiment in which the set value of the solder amount (V) of the solder fillet is the minimum. By considering the cylindrical concave surface of the side surface electrode 2 as a flat surface and calculating the solder flow on the side surface portion of the fillet as a straight line, the amount of solder is obtained by the following formula. Vmin = ra.rb.wa / 2 + ra.rb (wb-w
a) / 6

Next, FIG. 2 shows an embodiment in which the solder surface is formed to have a roundness due to the surface tension, and shows the maximum setting of the solder amount (V) in the present invention.

The cross-sectional shape is a 4-division circle or 4-division ellipse,
By calculating the shape of the side surface electrode and the solder flow on the side surface portion of the fillet in the same manner as described above, the amount of solder is obtained by the following formula. Vmax = π ・ ra ・ rb ・ wa / 4 + π ・ ra ・ rb
(Wb-wa) / 12

Based on the above, in the present invention, the amount of solder is
(V) is set as in the following equation. ra ・ rb ・ wa / 2 + ra ・ rb (wb-wa) / 6
<V <π ・ ra ・ rb ・ wa / 4 + π ・ ra ・ rb (w
b-wa) / 12 To give an example of the electrode dimensions of the embodiment of FIGS. 1 and 2, ra: 250 μm rb: 250 μm ra: 250 μm rb: 250 μm And the amount of solder in this case is calculated by the above equation,
It looks like the one below. In case of Figure 1: Vmin = 7812500μm³ ≈ 0.0078 mm³ In the case of FIG. 2: Vmax = 12265625 μm³ ≈ 0.0123 mm³

As in the case of FIG. 2, it is optimal to make the height ra of the side surface electrode 2 and the length rb of the mounting portion electrode equal in order to obtain a shape utilizing surface tension. Since the tolerance in this case is about 40 μm, consider them and take r
The setting range is a / rb = 0.7 to 1.3.

Further, in order to secure a large bonding area, the side electrode width (wa) ≦ the mounting portion electrode width (wb).

Next, when the mounting structure of the present invention is set by the distance (L) from the point where the side surface electrode contacts the mounting portion electrode to the solder surface, as described above, the minimum value is
Lmin = ra ・ rb / (ra ² + Rb ² ) ^1/2 Given in.

On the other hand, the set maximum value includes the case of the shape according to the surface tension as in the embodiment of FIG. 2, and in consideration of the case where the shape is distorted, the square cross section is expressed by the following equation. As a value corresponding to the diagonal length of Lmax = (ra ² + Rb ² ) ^1/2 I am trying.

For the electrode dimensions of the above embodiment, these values are Lmin = 177 μm and Lmax = 354 μm.

As described above, by forming the solder fillet by setting the solder amount (V) or the distance (L), a thick solder portion having sufficient strength can be obtained. for that reason,
Even if a solder crack is generated on the lower surface of the package and reaches the fillet portion, the stress is dispersed and the spread of the crack to the important fillet portion is prevented.

[0031]

As described above, the amount of solder or the distance (L) from the point where the side surface electrode contacts the mounting portion electrode to the solder surface is set by the mounting structure and mounting method of the present invention. Since strong joints can be formed by joining, it is possible to prevent the occurrence of cracks that were easily generated in a small package with conventional fillet-shaped fillets, and to achieve highly reliable solder joints. Obtainable.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of a semiconductor package mounting structure of the present invention.

FIG. 2 is an explanatory view of another embodiment of the semiconductor package mounting structure of the present invention.

FIG. 3 is an explanatory diagram of an electrode configuration of an LCC package and a mounting board.

FIG. 4 is an explanatory diagram of a conventional semiconductor package mounting structure.

[Explanation of symbols]

1: Semiconductor package, 2: Side electrode, 3: Mounting part electrode, 4: Solder

Claims (4)

[Claims] 1. In a mounting structure in which a semiconductor package having a side surface electrode is soldered to a mounting board, a height of the side surface electrode is ra, a width is wa, and a length of a mounting portion electrode of the mounting board is rb. , Wb, the mutual relationship of the electrode dimensions is expressed as ra / rb = 0.7 to 1.
3. A packaging structure for a semiconductor package, characterized in that wa ≦ wb, and the joint solder fillet is formed with a solder amount (V) satisfying the following formula. ra ・ rb ・ wa / 2 + ra ・ rb (wb-wa) / 6
<V <π ・ ra ・ rb ・ wa / 4 + π ・ ra ・ rb (w
b-wa) / 12 2. In a mounting structure in which a semiconductor package having a side electrode is soldered to a mounting substrate, the height of the side electrode is ra, and the length of a mounting portion electrode of the mounting substrate is rb, In the solder section,
A mounting structure of a semiconductor package, wherein a solder fillet is formed so that a distance (L) from a point where the side surface electrode contacts the mounting portion electrode to a solder surface satisfies the following expression. ra ・ rb / (ra ² + Rb ² ) ^1/2 <L <(ra ²
+ Rb ² ) ^1/2 3. A mounting method for soldering a semiconductor package having a side electrode to a mounting substrate, wherein the side electrode has a height ra and a width wa, and a mounting portion electrode length of the mounting substrate is rb. , Wb, the mutual relationship of the electrode dimensions is expressed as ra / rb = 0.7 to 1.
3. A method of mounting a semiconductor package, characterized in that wa ≦ wb, and forming a joint solder fillet with a solder amount (V) satisfying the following formula. ra ・ rb ・ wa / 2 + ra ・ rb (wb-wa) / 6
<V <π ・ ra ・ rb ・ wa / 4 + π ・ ra ・ rb (w
b-wa) / 12 4. A mounting method for soldering a semiconductor package having a side electrode to a mounting substrate, wherein the height of the side electrode is ra and the length of a mounting portion electrode of the mounting substrate is rb, In the solder section,
A method for mounting a semiconductor package, wherein a solder fillet is formed so that a distance (L) from a point where the side surface electrode contacts the mounting portion electrode to a solder surface satisfies the following expression. ra ・ rb / (ra ² + Rb ² ) ^1/2 <L <(ra
² + rb ² ) ^1/2