JP5310309B2 - Solder coat lid - Google Patents

Description

  The present invention relates to a solder coat lid for sealing a semiconductor device, and more particularly to a solder coat lid provided with a solder alloy coat having excellent adhesion to a lid substrate.

In recent small electronic devices such as mobile phones and mobile computers, it is required to reduce the size and thickness of an internal electronic circuit unit.
In particular, semiconductor devices mounted inside, such as semiconductor circuits, IC chips, crystal resonators, SAW filter elements, and other external devices such as heat, vibration, and deformation during manufacturing are reduced by making them smaller and thinner. In addition, the fact that the elements are mounted close to each other is one of the causes of such a problem.

  A sealing technique developed as a means for solving such a problem is to seal a semiconductor device in a sealed space as one unit. A solder coat lid for sealing is used at that time.

  The solder coat lid is a lid (lid) provided with a solder coat on the back surface of the lid. Providing a solder coat on the back of the lid in advance facilitates soldering when sealing using solder. After the semiconductor device is sealed, when the sealed semiconductor device is mounted on a circuit board or the like by reflow or flow processing, the solder alloy used for the soldering for sealing or the solder alloy coated on the lid does not remelt. It is important to do so.

Even in the past, such lead-free solder coat lids have been proposed.
Patent Document 1 proposes a solder coat lid in which an Sn—Sb-based solder alloy is hot-plated on the back side of a sealing lid.

JP 2002-184886 A

Here, with the recent technological progress, the required characteristics for lead-free solder coat lids are also increasing, and today, the following characteristics are required.
(A) A lead-free solder alloy having a solidus temperature of 240 ° C. or higher and a liquidus temperature of 260 ° C. or higher, so-called high-temperature solder, because not only the mounting temperature tends to increase but also the mounting frequency tends to increase. There is a demand for sealing soldering.
(b) The conventional lid was, for example, a size of 6.8 mm × 4.4 mm, but compared with such a conventional lid, the recent one is 1.7 mm × 1.7 mm, such as the lid itself. The shape of is getting smaller. When a lid having such a small shape is punched out from a blank material with a press, the solder coat itself or the joint surface with the base material may be isolated.
(c) Depending on the type of lid, drawing may be performed simultaneously with punching by press processing or prior to punching of press processing, and the overall shape may be a cap shape (also called a hat shape). Further improvement in the adhesion between the solder coat and the substrate is required. At the same time, excellent workability is required for the solder alloy itself.

  When a conventional Sn—Sb solder alloy is used, the Sn—Sb solder alloy has a relatively low liquidus temperature of 240 to 243 ° C., and the heating temperature during the mounting operation performed after the package sealing is 210. It is very limited such as below ℃.

  However, under the circumstances as described above, where the mounting temperature is high and the number of mountings is increased as described above, a solder alloy which is a high-temperature solder and has improved workability such as punchability and drawability is required.

  Therefore, in order to provide a solder coat lid that satisfies the characteristics that are strongly demanded today, a solder alloy having a liquidus temperature of 260 ° C. or higher and having excellent workability at the time of molding the solder coat lid is used. I knew it was necessary.

Here, the general subject of this invention is providing the solder coat lid for the sealing of the ceramic package which can implement | achieve size reduction and thickness reduction effectively.
A more specific problem of the present invention is to provide a solder coat lid using a solder alloy having a liquidus temperature of 260 ° C. or higher, and more preferably excellent in punchability, more preferably in drawing workability.

  The present inventors have focused on Bi-Sn-based high-temperature solder. In general, the Bi-Sn system has a melting temperature of about 260 ° C., and is hardly affected by heat when the semiconductor device after sealing is mounted on a circuit board.

However, actually, when a solder coat lid was manufactured by a hot-dip plating method using a Bi-Sn solder alloy, it was found that there was a problem in adhesion to the Kovar material as a base material.
For soldering to Kovar, it is usually necessary to perform Ni plating as a base treatment, but this Ni reacts with Bi of the solder alloy to form the intermetallic compound Bi ₃ Ni. It was found that the base material and the solder alloy layer were peeled from the intermetallic compound generation region, and a solder joint portion having sufficient strength could not be obtained.

  Therefore, the present inventors have found that the LiCu intermetallic compound is produced even in the case of Cu, but the adhesion is not lowered when Cu plating is performed instead of expensive Ni plating on the lid base material. It was.

  In addition, the BiCu intermetallic compound is excellent in adhesion to the lid base material, so it does not become a starting point for cracking during punching, shearing such as drawing, or bending / tensioning such as drawing. The inventors have found that it is possible to arrive at the present invention.

The reason why such a result appears is that the BiCu intermetallic compound is more flexible than the BiNi intermetallic compound, and Bi reacts selectively with Ni rather than Cu, and BiNi intermetallic compound It is mentioned that the growth rate of the compound is fast.
Therefore, when using a Bi-based solder material, it is considered that using a Ni-based base material tends to form a thick BiNi intermetallic compound and become brittle.

Here, the present invention is as follows.
(1) A Ni base substrate constituting the lid body, a Cu plating layer provided on the Ni base substrate, a Bi-Sn solder alloy layer provided on the Cu plating layer , and the Bi A solder coat lid for sealing a semiconductor device, wherein the Sn solder alloy layer is made of a Bi-Sn solder alloy consisting of Sn: 0.5 to 5.0% by mass and the balance Bi .
(2) the Ni base substrate is composed of a nickel alloy (1) Symbol placement of the solder coat lid.
( 3 ) The solder coat lid according to (1) or (2) , wherein the semiconductor device is a crystal resonator.
( 4 ) The solder coat lid according to (1) or (2) , wherein the semiconductor device is a SAW filter.
( 5 ) The solder coat lid according to any one of (1) to ( 4 ), wherein the longitudinal cross-sectional shape is a hat shape.

According to the present invention, since it is lead-free, there is no adverse effect on the environment that is a problem today.
In the present invention, so-called high-temperature solder is used as a solder coat, so that even when the mounting temperature is set high or when the mounting frequency is large, highly reliable mounting can be performed. it can.

It is typical explanatory drawing of the cross-sectional structure of the solder coat lid concerning this invention. FIG. 2A is a schematic explanatory diagram of a flat solder coat lid, and FIG. 2B is a schematic explanatory diagram of a hat type solder coat lid. It is typical explanatory drawing of a part of manufacturing process of the solder coat lid concerning this invention. It is a surface optical micrograph of the punching end surface of the solder coat lid obtained by the Example of this invention. It is the cross-sectional SEM photograph of the lid of an Example similarly. FIG. 6 is a surface optical micrograph of the same punched end surface as in FIG. 4 of the solder coat lid obtained by the comparative example. Similarly, FIG. 5 is a cross-sectional SEM photograph of the comparative example. It is a surface optical microscope photograph which shows the result of the crosscut test of the Example of this invention. It is a surface optical microscope photograph which shows the result of the crosscut test of the comparative example of this invention.

Next, the present invention will be described more specifically.
FIG. 1 is a schematic explanatory view showing a cross-sectional structure of a solder coat lid (simply called “lid”) 10 according to the present invention. The lid 10 is composed of a nickel base material 1 such as Kovar, and has a planar size of, for example, about 2 mm × 2 mm. FIG. 1 schematically shows an enlarged partial cross-section.
A Cu plating layer 2 is provided on the nickel base 1. On the Cu plating layer 2, a Bi-Sn solder alloy coat 3 (also simply referred to as "solder coat") is provided. The upper side of the drawing is the back surface of the lid 10. When there is time before providing a solder coat after performing Cu plating on the nickel substrate 1, or when storing temporarily, Sn plating is performed on the Cu plating layer 2 to oxidize the surface of the Cu plating layer. May be prevented to ensure solder wettability of the Cu plating layer 2.

In the illustrated example, the Cu plating layer is directly bonded to the nickel base material 1, but the nickel base material 1 may be provided with Cu plating on the nickel base material 1 by using a nickel plating material beforehand. The solder coat 3 constituting the uppermost layer may be provided by being bonded to the Cu plating layer to prevent the generation of Bi ₃ Ni intermetallic compound. Therefore, to that extent, the embodiment includes a case where nickel plating is performed on the nickel base 1 or a case where Sn plating is further performed thereon.

The Cu plating layer is usually provided by electrolysis or electroless plating, but is not particularly limited thereto as long as thin plating is possible.
FIG. 2 is a schematic explanatory view of a mode in which the semiconductor device is sealed using a lid. In the drawing, the semiconductor device 24 is mounted in the recess 22 of the ceramic package 20. Although not shown, the package 20 is appropriately provided with a circuit and electrically connected to the semiconductor device.

  FIG. 2A shows the case of a flat solder coat lid 26. FIG. 2B shows a case where the lid 28 is a cap type (hat type). 2A and 2B, the same members are denoted by the same reference numerals.

In this specification, a substrate that houses or mounts the semiconductor device 24 is referred to as a package base or simply as a package 20.
The kind of the semiconductor device hermetically sealed with the lid according to the present invention is not particularly limited, and includes a general semiconductor device used by being sealed in a package. Various devices such as a semiconductor circuit, a semiconductor element incorporating a wafer, an IC chip, a crystal vibration element, and a SAW filter are exemplified. It is particularly suitable as a semiconductor device sealed with.

  The package base 20 is made of an electrically insulating material that can withstand the heating temperature during solder melting. A typical example of a material satisfying such characteristics is ceramics. Therefore, the lid of the present invention is typically used for sealing a ceramic package in which the package base is made of a ceramic material.

  The ceramic material of the ceramic package may be any material conventionally used for ceramic packages, such as alumina, aluminum nitride, mullite, glass ceramic, and the like. Of course, the ceramic substrate may be a multilayer substrate, and there are no restrictions on the method for producing the substrate, the method for forming the inner layer wiring, and the like.

  As shown in FIG. 2A, when the lid of the present invention is plate-shaped, the package base has a recess 22 in which a semiconductor device 24, for example, a crystal resonator is mounted. Then, a lid 26 having a size that completely covers the recess 22 is placed on the recess, and in this state, the solder coat 3 is then heated and melted, and the interface between the lid and the package base is sealed with lead-free solder. It stops.

On the other hand, as shown in FIG. 2 (b), when the package base is flat, the lid of the present invention is a cap type.
Referring to FIG. 2 (a) as an example, when the insulating package substrate is a ceramic substrate, the ceramic substrate does not have bondability (wetting properties), and therefore the portion to be sealed of the substrate, that is, the above-described recess is not provided. It is necessary to form an appropriate metal layer 21 having excellent bonding properties as a base on the upper surface of the base that surrounds and bonds with the lid to form the sealing portion 23. The metal layer 21 is preferably formed by performing metallization with a refractory metal such as W or Mo and then applying Ni plating and Au plating from the viewpoint of securing the bonding property. However, the underlying metal layer is not limited to this, and other metal layers that can be used for ceramic packages that are sealed with solder can also be applied.

  In the case of the present invention, as described above, the bonding strength and processing characteristics at the bonding surface between the nickel base substrate forming the lid body and the solder coat 3 are important, but the package The bonding characteristics between the metal layer 21 and the solder coat 3 are not particularly problematic as long as solder wettability can be secured in the metal layer.

  When the solder coat lid 26 according to the present invention is used, a metal layer 21 of W—Ni—Au is provided on the upper end portion 21 of the package 20, and the solder coat lid 26 is directly placed on the metal layer 21 and heated to be sealed. It can be performed.

  In this example, the solder coat 3 is provided on the entire lower surface of the lid 26. However, the solder coat 3 is applied only to a region that is in direct contact with the joining portion of the metal layer 21 at the upper end of the package or a region slightly larger than that. You may make it provide. In that case, the amount of solder required for the coating is reduced, and not only the material cost is reduced, but also the opportunity for volatilization of the solder component is reduced, and the deterioration of the characteristics of the internal mounted element due to the sealing can be avoided.

  Therefore, the solder coat lids 26 and 28 of this embodiment according to the present invention also include an embodiment in which the solder coat 3 is provided only in the region to be joined to the metal layer 21 at the upper end portion of the package 20.

  According to the present invention, the lid that covers the package substrate containing the semiconductor element is composed of a nickel-based base material in which a lead-free solder alloy is hot-plated on one surface of a metal plate. This nickel-based substrate constitutes the lid body, and the lead-free solder alloy that is hot-plated on this substrate is heated and melted during sealing to form an airtight seal between the lid and the package substrate To do. The preferred thickness is about 0.05 to 1 mm for the substrate and about 10 to 80 μm for the solder coat layer.

  FIG. 3 is a schematic explanatory view of the manufacturing process of the solder coat lid according to the present invention by the melting method. In the figure, the molten solder bath 30 accommodated in the solder bath 31 is filled with Kovar material, 42 alloy, or 45 alloy. A metal strip 32 obtained by performing Cu plating on a nickel base substrate such as a material is run in the direction of the arrow, and is continuously dipped and pulled out through a support roll 34, a dipping roll 36, and a take-out roll 38, thereby showing an example in the figure. Then, on one surface thereof, hot dip plating is performed to provide a solder coat 3 made of lead-free solder as shown in FIG. In the present specification, providing the solder layer in this way is referred to as “solder hot-dip plating” or “hot solder plating”.

Prior to the illustrated solder hot dipping step, Cu plating is applied to the Ni base substrate. Cu plating is performed in order to prevent the formation of Bi ₃ Ni intermetallic compounds, and may be electroplating or electroless plating. Plating is preferred.

  When hot-dip plating is performed subsequent to Cu plating, it is not always necessary, but in order to prevent surface oxidation of the Cu-plated surface, Sn plating, Au plating, or a rust preventive agent such as imidazole is applied. Since such a rust preventive layer is very thin, it will almost disappear during the subsequent hot dip plating of the solder alloy, so that no mention is made as a solder coat lid.

  In this way, the metal strip provided with the solder coat 3 only on one side is then molded into a lid 26 having a predetermined shape by a punching process such as a press in a molding process. After the inspection in the inspection process, it is used as it is as a solder coat lid for a semiconductor device package.

Alternatively, further, secondary processing such as drawing is performed as necessary to obtain a cap-type solder coat lid 28.
The solder coat lid for hermetic sealing of a semiconductor package according to the present invention is coated with a soft solder alloy layer, and has good handling properties at the time of punching, drawing or after.

Therefore, the lead-free solder coat lid according to the present invention can be easily mass-produced and has excellent handling properties.
The nickel base substrate to be the lid is not particularly limited, but preferably has a thermal expansion coefficient close to that of the package substrate. In the case of a ceramic package in which the substrate is ceramic, examples of preferable materials for the nickel base substrate used as the lid body include 42 alloy (Fe-42Ni alloy), 45 alloy, Kovar (Kovar, Fe-29Ni-17Co alloy). ) Etc.

Composition of the solder used in the present invention is a Bi-Sn alloy. A specific composition example is Sn: 0.5 to 5.0% by mass and the balance Bi. Preferably, Sn: 0.5 to 2.0% by mass and the balance Bi.

  In particular, in the case of a lead-free solder alloy consisting of Sn 2% and the balance being substantially Bi, the peak temperature is 265 ° C., which is a higher melting point than the mounting solder, and also when mounting after the soldering of the lid It does not melt.

  The solder coat lid according to the present invention is used for sealing a package containing a general semiconductor device, and a crystal resonator is advantageous as a mounting element at that time. In addition, IC chips and SAW filter elements can be considered.

In this example, a solder having a Bi-0.5Sn composition was coated (coated) on the surface of a lid made of a Kovar material by hot dipping to obtain a solder coat lid.
After Cu was plated to a thickness of 2.5 μm by electroplating in advance on only one surface of a Kovar belt (width 10 mm, thickness 0.05 mm), Sn plating was further performed and temporarily stored.

  Next, the hot-dip plating of lead-free solder was performed by the hot-dip plating process shown in FIG. The solder coat was formed only on the surface plated with Cu. This is because Kovar, which is a base material, is a material that does not inherently have solder attached thereto.

As a comparison, a solder coat lid obtained by performing Ni plating (electrolytic plating) on the substrate surface was also manufactured by the same method in which Cu plating was replaced with Ni plating.
Each solder coat lid was subjected to a punch test and a cross cut test.

The punching size was 5.4 mm X 5.4 mm X 0.08 mm. Punching was performed with the solder coat surface facing up.
As a result of the punching test, in the case of the test material in which Bi-0.5Sn hot-dip plating was performed on the base plated with Cu according to the present invention (Example), burrs and cracks were observed in all of the five punching tests. I couldn't.

On the other hand, in the case of the test material in which Bi-0.5Sn hot-dip plating was performed on the Ni plating base (Comparative Example), burrs and cracks were observed in all of the five punching tests.
The burr is a kind of surface flaw that appears at the end of the joint between the base material and the solder coat layer, that is, the end face of the punched material, and the crack is the joint between the base material and the solder coat layer. It is one type of peeling seen at the end of the part.

About each of an Example and a comparative example, the surface optical microscope photograph and cross-sectional SEM photograph of a test material are shown as FIG. 4 thru | or FIG.
4 and 5 are a surface optical micrograph and a cross-sectional SEM photograph, respectively, of the solder coat lid according to the present invention, but there are no burrs and no cracks. In FIG. 5, the solder coat that appears white in the figure is provided on both sides of the base material, but this is provided only for the purpose of seeing the influence from the upper and lower sides of the punching process by providing the solder coat on both sides as a test. It is.

  6 and 7 are a surface optical micrograph and a cross-sectional SEM photograph of the solder coat lid of the comparative example, respectively, and burrs and cracks are seen. In FIG. 6, the punched end face is stepped, and a burr is observed as a discontinuous portion at the top. The front surface of the photograph is observed as a crystalline state (dendrites) on the surface of the solder coat. In FIG. 7, the crack is observed as a protrusion partly protruding from the tip.

  FIG. 8 and FIG. 9 are surface optical micrographs showing the results of the cross-cut test of Examples and Comparative Examples of the present invention, respectively. The crosscut test was performed according to JISK5600-5-6, and 10 × 12 crosscuts were made at 1 mm intervals (9 × 11 = 99 squares), and the peeling state at that time was observed.

FIG. 8 shows an example of the present invention, and the classification according to the JIS standard was “0 (zero)”. FIG. 9 is a comparative example, and the classification was “2”.
In the example of the present invention, the adhesion between the solder coat and the base material is excellent. From these results, it is judged that peeling of the solder coat does not occur even when the hat-type solder coat lid is formed by drawing.

Claims (5)

And Ni-based base material constituting the lid body, and a Cu plating layer provided on the Ni base substrate is composed of a Bi-Sn solder alloy layer provided by bonding to the Cu plating layer, the Bi A solder coat lid for sealing a semiconductor device, wherein the Sn solder alloy layer is made of a Bi-Sn solder alloy consisting of Sn: 0.5 to 5.0% by mass and the balance Bi . The Ni base substrate, according to claim 1 Symbol placement of solder coating the lid consists of a nickel alloy. The semiconductor device, the solder coating lid according to claim 1 or 2 which is a crystal oscillator. The semiconductor device, the solder coating lid according to claim 1 or 2 is a SAW filter. Longitudinal section forms a hat-solder-coated lid according to any one of claims 1 to 4.