JP3314741B2 - Semiconductor package assembly and method of assembling the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor package in which a semiconductor package such as a ball grid array (BGA) or a chip size package (CSP) can be firmly mounted on a mother substrate such as a resin substrate or a ceramic substrate. Open to assembly.

[0002]

2. Description of the Related Art In recent years, with the increase in the number of pins in a semiconductor package, a ball grid array (BGA) and a chip size package (CSP) have been used in various fields. This type of ball grid array or chip size package is manufactured by mounting a bare chip on the surface of a resin substrate such as BT resin or a ceramic substrate or an interposer substrate such as a TAB tape and fixing a spherical solder called a BGA ball on the back surface to manufacture a semiconductor. It is usually shipped from the manufacturer.

[0003] Such a semiconductor package is mounted on a mother substrate on which cream solder is printed in advance in a mounting process, and is passed through a reflow furnace. FIG.
(A), (B) is a cross-sectional view showing an example of a conventional semiconductor package assembly before and after mounting, respectively. As shown in FIG. 1B, the semiconductor package assembly 1 assembled in a mounted state has an interposer substrate 2 having an interposer-side pad 2a on a lower surface (back surface) and a mother-side pad 3a on an upper surface (front surface). The BGA ball 4 and the cream solder 5 are interposed between the mother board 3 having the above structure and the mother board 3. In the case of this example, each of the pads 2a and 3a is a copper foil on which a predetermined circuit pattern is printed and formed, that is, a Cu pad.

In manufacturing the semiconductor package assembly 1, first, an interposer substrate 2 having a connection BGA ball 4 fixed to a lower surface is prepared. Next, a mother substrate 3 on which the interposer substrate 2 is to be assembled is prepared, and cream solder 5 is printed and applied on mother-side pads 3a formed on the upper surface of the mother substrate 3. Next, the interposer substrate 2 is mounted on a mounter, the lower surface of the interposer substrate 2 is held on the upper surface of the mother substrate 3 at a predetermined interval in a predetermined positional relationship, and the lower end of the BGA ball 4 is positioned at a predetermined position of the mother-side pattern 3a. Pass through the reflow furnace in the abutted position. On the substrates 2 and 3 which have passed through the reflow furnace while being held opposite to each other in a predetermined positional relationship, the cream solder is melted and solidified, and the BGA balls 4 form an intermetallic compound by wet back. At this time, the BGA ball 4 is compressed by the weight of the semiconductor package or by a compression deformation caused by a predetermined pressure.
Is deformed into a barrel shape, and performs adhesion and conduction between the interposer substrate 2 and the mother substrate 3.

[0005]

In the conventional semiconductor package assembly 1 described above, the connection BGA balls 4 interposed between the mother substrate 3 and the interposer substrate 2 are melted and solidified by passing through a reflow furnace to form a barrel. It is transformed into a shape,
The pads 3a on the mother board 3 and the pads 2a on the interposer board 2 are made of copper foil, while the BGA balls 4
Is made of a solder alloy containing Sn and Pb in a weight ratio of, for example, 5:95, and therefore, there is a difference in the thermal expansion coefficient between the pads 2a and 3a and the BGA ball 4. Therefore, the interface between the pad 3a on the mother substrate 3 and the BGA ball 4 or the BG
At the interface between the A-ball 4 and the pad 2a on the interposer substrate 2, residual thermal stress is generated based on a difference in thermal expansion,
This has the problem of giving stress to the interface. In particular, when the semiconductor package assembly 1 is incorporated in an ECU unit that is heavily used in a severe environment such as an engine room that is susceptible to vibrations at high temperature and high humidity, the pad 2 due to the stress based on the difference in thermal expansion.
Solder cracks are likely to occur at the interface between the a and 3a and the BGA ball 4, and the locations where the solder cracks occur cause the wound to expand due to vibration, and as a result, peeling at the interface proceeds.
There were issues such as difficulty in ensuring the long-term quality.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to enable a mother board and an interposer board to be rigidly and firmly assembled with a columnar core instead of a BGA ball.

[0007]

In order to achieve the above object, a semiconductor package assembly according to the present invention comprises a mother board and an interposer board which is held with its lower surface facing the upper surface of the mother substrate by a predetermined distance. In a state where the upper end surface is joined to the lower surface of the interposer substrate, the periphery of the upper end surface is soldered and fixed by a solder fillet made of high-temperature solder, and the lower end surface is joined to the upper surface of the mother substrate. ingredients and soldered fixed columnar core by a solder fillet formed of a lower end surface periphery from eutectic solder
The columnar core is provided on an upper surface of the mother substrate.
Part and the lower surface part of the interposer substrate and the thermal expansion coefficient.
It is characterized by being made of similar materials .

Further, the method of assembling a semiconductor package assembly according to the present invention is characterized in that the lower surface of the interposer substrate which holds the lower surface of the interposer substrate facing the upper surface of the mother substrate by a predetermined distance.
A material having a thermal expansion coefficient close to that of the lower surface of the interposer substrate
The upper end surface of the columnar core made of is joined, and in this state, a solder fillet made of high-temperature solder is formed around the upper end surface,
First to fix the columnar core to the interposer substrate by soldering
And applying a paste-like eutectic solder to the upper surface of the mother substrate, and bonding the lower end surface of the columnar core integrated with the interposer substrate in the first process to the upper surface of the mother substrate. A second step of forming a solder fillet made of eutectic solder on the periphery of the lower end face through a reflow furnace and soldering and fixing the columnar core to a mother substrate.

[0009]

An embodiment of the present invention will be described below with reference to FIG. 1A and 1B are cross-sectional views showing states of a semiconductor package assembly according to an embodiment of the present invention before and after mounting, respectively.

A semiconductor package assembly 11 shown in FIGS. 1A and 1B uses a columnar core 14 in place of a conventional BGA ball 4 and uses an interposer substrate 12 and a mother substrate 1.
3 is intended to be connected. As the columnar core 14, the same metal material as the pad 13a on the mother substrate 13 or the pad 12a on the interposer substrate 12 is used. Here, copper, which is the same material as the copper foil forming the conductive pattern, is processed into a cylindrical shape. Things are used.

The semiconductor package assembly 11 shown in this embodiment includes a mother board 13, an interposer board 12 whose lower face is opposed to the upper face of the mother board 13 by a predetermined distance, and an interposer board 12. With the upper end surface joined to the lower surface, the periphery of the upper end surface is soldered and fixed by a solder fillet (hereinafter, referred to as a high-temperature solder fillet) 16 made of high-temperature solder, and the lower end surface is joined to the upper surface of the motherboard 13. In this state, the lower end surface periphery is formed of a columnar core 14 which is soldered and fixed by a solder fillet 17 made of eutectic solder (hereinafter referred to as a eutectic solder fillet) 17.

The manufacturing process of the semiconductor package assembly 11 includes a first process and a second process. First, in the first step,
The columnar core 14 is fixed to the lower surface (back surface) of the interposer substrate 12 of a ball grid array or a chip size package by using a high-temperature solder according to a predetermined grid pattern. In this case, a high-temperature solder fillet 16 is formed around the upper end surface of the columnar core 14, that is, around the joint interface with the interposer substrate 12. In addition, as high-temperature solder,
A solder alloy containing Sn, Pb, Cd, Ag, Zn, and the like in an appropriate composition ratio is used, and its melting temperature needs to be higher than the furnace temperature of the reflow furnace used in the second step. Also, the high-temperature solder fillet 16 formed of this high-temperature solder serves as a fillet to contribute to the connection strength.
It is formed so as to have a predetermined drum shape shown in FIG.

In a first step, the interposer substrate 12
The columnar core 14 is assembled in a state where the lower end surface is joined to the upper surface of the mother substrate 13 by a mounter (shown) in the next second step. However, before this assembling, cream solder 15 made of paste-like eutectic solder is printed and applied on the mother-side pads 13a formed on the surface of the mother substrate 13. As the eutectic solder, for example, a solder alloy containing Sn and Pb at a weight ratio of 62:32 is used, and when the temperature is gradually lowered from the molten state, the eutectic point (183.3 ° C.) is reached. It shows the property of solidifying instantaneously when it is used. It is also an important property that when the temperature is raised from room temperature, the temperature at which the liquid is completely liquefied is the lowest temperature among the Sn-Pb-based solders. Therefore, the interposer substrate 12 is
3 and when passed through a reflow furnace in this state, only the cream solder 15 is melted and solidified without melting the already formed high-temperature solder fillet 16, and a portion thereof is formed along the side surface of the columnar core 14. Fig. 1
As shown in (B), a drum-shaped eutectic solder fillet 17 is formed around the lower end surface of the columnar core 14, that is, around the joint interface with the mother substrate 13.

As described above, in the semiconductor package assembly 11, the interposer substrate 12 is assembled to the mother substrate 13 by using the columnar core 14 instead of the conventional BGA ball 4, so that the columnar core 14 The distance between the interposer substrate 12 and the columnar core 1 can be maintained at a predetermined distance between the
A high-temperature solder fillet 16 is formed around the interface with the metal substrate 3 and a eutectic solder fillet 17 is formed around the interface between the mother substrate 13 and the columnar core 14, so that both end surfaces of the columnar core 14 are interposers. Although it is only joined to the board 12 and the mother board 13, a sufficient connection strength can be obtained by the solder fillets 16 and 17 surrounding the joining interface.

The columnar core 14 soldered and fixed to the interposer substrate 12 by high-temperature solder is aligned with a mother substrate coated with a paste-like eutectic solder (cream solder 15), and then passed through a reflow furnace to provide a high-temperature solder. The eutectic solder fillet 17 can be firmly soldered and fixed to the mother board 13 without worrying about melting of the solder fillet 16, and the eutectic solder fillet 17 formed with sufficient eutectic solder has sufficient connection strength, Since it is free from solder cracks caused by residual thermal stress as in the conventional BGA ball 4, it is possible to maintain a robust connection state for a long period of time.

Further, since the columnar core 14 is made of the same material as the upper surface of the mother substrate 13 and the lower surface of the interposer substrate 12, the mother substrate 13 is passed through a reflow furnace.
When the interposer substrate 12 and the interposer substrate 12 are combined via the columnar core 14, both end surfaces of the columnar core 14 are joined to the same material, so that there is no difference in thermal expansion based on the difference in coefficient of thermal expansion. Since the stress due to the thermal stress is reduced, there is little possibility that the connection strength is reduced due to the solder crack. For this reason, even when the semiconductor package assembly 11 is incorporated in an ECU unit that is heavily used in a harsh environment, such as an engine room, which is susceptible to vibration at high temperature and high humidity, the stress based on the difference in thermal expansion as in the past is not affected. Solder cracks are generated due to the cause, and the locations where the solder cracks are generated do not enlarge the wound due to vibration, and peeling at the interface does not progress, so that long-term quality can be ensured.

In the above embodiment, a ball grid array (BGA) or a chip size package (CSP)
Although the interposer substrate 12 attached to the above has been described as an example, the interposer substrate 12 may be used for another semiconductor package. In addition, high-temperature solder and eutectic solder
Those having compositions other than those described in the embodiment can also be used. Furthermore, in the above embodiment,
The columnar core 14 is not limited to copper, and may be formed of another material having a thermal expansion coefficient close to copper or a material having physical properties close to copper. In short, the pads 12a, 1
The columnar core 14 may be made of a material having physical properties close to 3a.

[0018]

As described above, according to the present invention,
Since the interposer board was assembled to the mother board using a columnar core instead of the conventional BGA ball,
The columnar core can maintain a predetermined interval between the interposer substrate and the mother substrate, and a solder fillet made of high-temperature solder is formed around the interface between the interposer substrate and the columnar core. Since a solder fillet of eutectic solder is formed around the interface, both end surfaces of the columnar core are only joined to the interposer board and mother board, but sufficient connection strength is provided by the solder fillet surrounding the joint interface The columnar core soldered and fixed to the interposer substrate by high-temperature solder is aligned with the mother substrate coated with paste-like eutectic solder and passed through a reflow furnace to melt the high-temperature solder fillet. Don't worry,
It can be securely soldered and fixed to the motherboard,
The eutectic solder fillet formed with sufficient wetting of the eutectic solder has sufficient connection strength and is free from solder cracks caused by residual thermal stress like conventional BGA balls. It has excellent effects such as being able to maintain a robust connection state.

Further, according to the present invention, since the columnar core is made of the same material as the upper surface portion of the mother substrate and the lower surface portion of the interposer substrate or a material having a close physical property such as thermal expansion coefficient,
When the mother substrate and the interposer substrate are combined via a columnar core through a reflow furnace, both end surfaces of the columnar core are bonded to the same material or a material having a close physical property value such as a coefficient of thermal expansion. Because the difference in thermal expansion based on the difference is less likely to occur and the stress due to residual thermal stress is reduced,
It is unlikely that solder cracks will cause a drop in connection strength, especially if it is installed in an ECU unit that is heavily used in a harsh environment that is susceptible to vibrations at high temperatures and humidity, such as the engine room. Cracks occur due to the stress based on the cracks, the places where the solder cracks occur expand the wound due to vibration, the peeling at the interface does not progress, and the long-term quality can be ensured, etc. Has the effect of

[Brief description of the drawings]

FIGS. 1A and 1B are cross-sectional views showing states of a semiconductor package assembly according to an embodiment of the present invention before and after mounting, respectively.

FIGS. 2A and 2B are cross-sectional views showing an example of a conventional semiconductor package assembly before and after mounting, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Semiconductor package assembly 12 Interposer board 12a pad 13 Mother board 13a pad 14 Columnar core 15 Cream solder 16 High temperature solder fillet 17 Eutectic solder fillet

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-5655 (JP, A) JP-A-8-31835 (JP, A) JP-A-10-261736 (JP, A) JP-A-9-99 17904 (JP, A) JP-A-10-256307 (JP, A) JP-A-63-152136 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 23/12 H01L 23 / 32 H05K 1/18

Claims (2)

(57) [Claims] 1. An interposer substrate having a lower surface spaced apart from the upper surface of the mother substrate by a predetermined distance, and an upper edge of the interposer substrate having an upper surface joined to the lower surface of the interposer substrate. together with the soldered by solder fillets made of high-temperature solder, and soldering fixed columnar core by a solder fillet formed of a lower end surface periphery from eutectic solder in a state of being joined to the lower end surface to the upper surface of the mother substrate comprising a result, the said columnar core has an upper surface portion and the Yi and the mother board
From a material with a thermal expansion coefficient close to that of the lower part of the interposer substrate
The semiconductor package assembly, characterized by comprising. 2. A predetermined distance between a lower surface and an upper surface of a mother substrate.
The lower surface of the interposer substrate
Has a thermal expansion coefficient close to that of the lower surface of the interposer substrate.
Join the top surface of the columnar core made of the material, and in this state
Form a solder fillet made of high-temperature solder around the top edge
And fix the columnar core to the interposer board by soldering
A first step, a paste-like eutectic on the upper surface of the mother substrate;
Solder is applied, and the interposer base is applied in the first step.
The lower end surface of the columnar core integrated with the plate is
To the upper surface, and pass it through a reflow furnace in this state.
Form a solder fillet made of eutectic solder around the end face,
Second step of soldering and fixing the columnar core to a mother board
A set of semiconductor package assemblies, comprising:
Standing method.