JPS5832088A - Silver-filled glass - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] FIELD OF THE INVENTION This invention relates generally to silver-metalization.

More particularly, the present invention relates to silver-filled glass compositions used specifically to bond silicon semiconductor devices to substrates.

Although the origin of silver-metallized compositions was in decorative enamelling,
Thick film: It was used early on for applications in hybrid electric circuit mechanisms. Early researchers' attention, however, was focused on designing compositions that strongly adhered to ceramic substrates. Ih Yuru” Scotch Teso Test 1
was the initial standard for adhesion. Knox U.S. Pat. No. 2.31. ! ;、! No. 10 discloses a lead borosilicate glass containing a high content of bismuth oxide. This has been used extensively for silver but has been insufficient for other precious metals. Hoffman, US Pat. No. 3.1Lt≠0.712, discloses the addition of vanadium and copper oxides to improve the adhesion, solderability and conductivity of precious metal metallization compositions. There is. These compositions have been used as conductors rather than as media for bonding devices such as silicon integrated circuits to substrates.

In this category, gold-based inks or preforms have been the most popular given the advantages of low temperature gold-silicon eutectic mixtures to achieve good bonding. Although considerable efforts have been made to reduce the amount of gold required to form such bonds, its high cost does not allow its use in all possible applications.

There is no low temperature phase in the silver-gold thread, it is a continuous phase of solid solution, and the silver-silicon system has a eutectic point but a high temperature (goo
above). Therefore, a system based entirely on 5-silver must actually utilize a fundamentally different bonding mechanism in which little or no involvement is involved in the pot itself.

Thus, when using a gold preform to adhere to a silicon die gold-silver metallized surface, the bonding mechanism is on the one hand gold-silicon eutectic formation and on the other hand solid-liquid diffusion; Glass plays a major role in bond strength. Since this is weaker than the metallurgical bond, the thermal conductivity as well as the electrical conductivity are lower than the predetermined values.

Pure glass bonds have also been used for this purpose, but as expected, without conductive elements both conductivities are impaired.

Silver polyimide compositions are also known for this use. However, the amount of silver that can be blended is limited, and special processing is required (for mass production, uniformity of processing is an important factor in determining costs). The biggest disadvantage of polyimide, or any organic binder system, is that they cannot be packaged airtight like Cerdips and the like. This is because they are hygroscopic, cannot degas, and generally cannot withstand the high temperatures required in forming these packages.

The present invention provides a silver-filled glass that provides a strong bond between a silicon die and a substrate, whether or not the substrate is metallized, and the silver-filled glass is heat-adjustable. It also has good electrical conductivity and can be used in an airtight package.

A general object of the present invention is to provide an improved medium for bonding silicon guineas to substrates.

Another object of the present invention is to metallize silicon or the like under normal processing conditions. It is an object of the present invention to provide a silver-filled glass that can be used to form a strong bond with a metal substrate.

Yet another object of the present invention is a silver-filled glass for bonding a silicon guinea with a substrate, which is less expensive than gold-based systems and has higher conductivity and bonding than other silver or non-metallic systems. The object of the present invention is to provide a silver-filled glass having high strength and suitable for use in a hermetic package.

Various other objects and advantages of the invention will become apparent from the following description of the embodiments. The novel features of the invention will also be pointed out with particular reference to the claims.

In selecting the silver powder to be used in the present invention, it has been found that both spherical and flake powders work well. However, flake powders are glossier and give a higher metallic appearance finish. It is interesting that some researchers have identified flakes as silver conductors, but as current carrying wires 1 rather than as coupling media.

Silver that is satisfactory for the present invention is from 0.7 to / m'/9
surface area within the range of 123-. It has a tag density (powder density) of 2.769/cc.

The glass is the second important component and it is essential that it has a low melting point so that it is in a molten state at the die-attach temperature, 0°C. A selected preferred glass meeting this requirement has a softening temperature of 3.23 °C and has the following composition: ZnOO,/j-OJ
O% 5in20. ,! j%, j% 8o balance 3 This glass is ground and fritted in a high purity alumina polish mill to meet the following specifications: Surface area 0.3-0. A m'/'9 Tap density 21g ~ 3 tails 97cc Generally, 323-
Softening point in the range of 1723°C and approximately /3ppm/°C
Glasses with coefficients of thermal expansion below, preferably in the range from g to /3 ppm/°C can be used. for example,
Glass can be mixed with bismuth oxide rather than lead oxide as the main component meeting the above criteria. Ikekata, any such glass should be sodium-free because of its affinity for silicon.

The softening point is at least 32 to ensure that all organic matter is incinerated! ; Must be ℃. If the softening point is higher than ≠Jj°C, the glass will not be sufficiently fluid at the die attach temperature. The glass is then mixed with a solvent as described below (0% solid molecules) and ground in a 3-roll mill to a particle size of 7 to gμ (F, O, G,).

Those skilled in the art will appreciate that the choice of solvent is not critical and that a variety of suitable solvents may be used. The solvent selected in this case contains 72% ethyl methacrylate and 72% terpineol.

Then 1.2! near! Silver is added to the glass paste at a predetermined silver to glass ratio discussed below, such that it falls within the limits of 0:20. Add more solvent to adjust the (total) solids percentage to 7J--4%,
- be used as a paint or ink. Since rheological problems occur outside this range, a solids content within the range of 10-43% is generally preferred.

The application of the paste is essentially the same as before.

The paste is applied to delimited areas, either dots or squares on metallized or intact film (ceramic) substrates depending on the application. When applied in the form of a dot, the size of the dot is about 2j% larger than the die. Die bonding is
Drying oven at 50°C for 75 minutes in air, then drying for 30 minutes
This is done by burning for 75 minutes at ℃. For the exam! The tube is subjected to a simulated (package) seal cycle within the range of 4'30~j, 2J1:. Additionally, the die may be bonded by conventional scrubbing techniques or may utilize hot-stage vibrational bonding techniques.

A surprising advantage of the invention is that the mechanical strength of the bond is proportional to the copper content. Standard bush test (pus
h test ) (Mll, 5pec, ll3F
3. Method 2θ/9. / ), it was found that the range of silver jj - IO% is 2.2 otr to ot, and 2 to 0g (j to /j pounds). As expected, the electrical conductivity is also improved by the silver content. At the lower limit, conductivity is determined by commercially available epoxy/based materials, such as EPO-TE.
This value is comparable to that of KP-10, and at the upper limit, it is approximately twice that value.

Problems can arise regarding the utility of low silver, high glass compositions related to the increase in both bond strength and conductivity with silver content. The answer to this generally depends on the intended use. More specifically, very good bonding is achieved for silver in the range of 25-4 to% when bonded by die or mechanical scrubbing means.

High silver content is preferred in situations where it is desired to submerge the die in the ink (or paste) to some extent. Upper limit of extremely high content (e.g. 75~go%)
In , tests have shown that the ink can be applied to the neat substrate and the support can be bonded by ultrasound with good results. It would generally be undesirable to use more than gO% silver. This is because the adhesive force begins to decrease. Thus,
There are various possibilities, including omitting certain processing steps, for example by gluing the lead frame and die together.

1. Various changes in the parts, steps, materials, and arrangement of Vζ parts described herein and illustrated for the purpose of explaining the invention may be obvious to those skilled in the art or may be claimed as such. It should be understood that the scope of the present invention falls within the scope of the invention.

2

Claims (7)

[Claims] (1) , 20-♂0% micronized silver near! ;-,20%
low melting point micronized glass frit; containing a suitable organic solvent, the proportion of solids in the silver-filled glass metal corrugated frit is about 7
Silver-filled glass metallized 4-strike, j to gj. (2) Silver has a surface area of 0.7~/, θll1j/9 and a tap density of 23−~λ, 7! ;9/cc. (3) A metallized paste according to claim 1, wherein the glass frit has a softening temperature in the range 32J-4.23C and a coefficient of thermal expansion in the range g~/3ppm/C. (4) The glass frit has a surface area in the range of 0.3 to 0.0, O♂/9 and a tap density in the range of 2 to 3.69/cc. ) Metallized paste described in section 2. (5) The glass frit is essentially KPbO9J--7j% ZnOO,/3;-0,,20% 5I020. ．． The metallized paste according to item (1) of the scope of Patent A Qingyuu, characterized in that it consists of 25 to 2 J% B2O3 balance. (6) The metallized paste according to claim (1), wherein the organic solvent consists of ethyl methacrylate 7.2% terpineol gg%. (7) , 2j -I 0%, 0.7~/, Om'
/9o surface area and j, , 2.5′~ノ, 739/cc
Finely powdered silver with a tap density of ! -20% of
Softening point range 3.2. t-1, 2,! t 1: micronized glass slit; and silver-filled glass metallized wave-
Solid connotation in strike? near! - 43% of a suitable organic solvent and a silver-filled glass metallization used to bond silicon semiconductor devices to a ceramic substrate.