JP5077690B2 - Au-Sn alloy solder paste for printing - Google Patents

Description

  In the present invention, Au-Sn alloy solder paste using Au-Sn alloy solder fine powder is applied by a printing method and reflowed to form Au-Sn alloy solder thinly and narrowly on the surface of a substrate or the like. It relates to an alloy solder paste.

  In general, a Au-Sn alloy solder paste as a lid bonding material for hermetically sealing a SAW filter, a crystal oscillator, etc. in a package mainly made of ceramics, a die bonding material such as LED, LD, PD, and MEMS, and an electrode material Is used.

The Au—Sn alloy solder paste is prepared by adding a flux to the Au—Sn alloy solder powder and stirring and mixing. And it is known that normally used Au—Sn alloy solder powder contains Sn: 15 to 25% by mass, and the balance is composed of Au and inevitable impurities, and this Au—Sn alloy solder powder is used. It is known that the powder is produced by gas atomization and that its average particle size D ₅₀ is in the range of 10-40 μm. A printing method is known as one of the methods for applying the Au—Sn alloy solder paste, and for example, a stencil printing method is known as one of the printing methods. In this stencil printing method, a stencil mask having narrow narrow through-grooves is placed on a substrate, the through-thin grooves of this stencil mask are filled with Au-Sn alloy solder paste, and then the stencil mask is removed. In this method, the Au—Sn alloy solder paste filled in the through-thin grooves is left on the substrate for printing (see Non-Patent Document 1).
In addition, a rosin-based flux based on rosin is used as the flux, and this rosin-based flux includes R (rosin flux consisting only of solvent and pure rosin), RMA (rosin-based flux with mild activity). ) And RA (activated rosin flux), classified and displayed on the market, and this classification is said to be derived from US federal standards (see Non-Patent Documents 2 and 3).
In Non-Patent Document 1, the RMA flux or non-halogen flux: 5 to 10% by mass, and the balance: Au—Sn alloy solder paste blended so as to be Au—Sn alloy solder powder has a viscosity of 50 to 250 Pa · s. It is described that it has.
Proceedings of the 10th Symposium on Microjoining and Mounting Technology in Electronics, Vol. 10.2004, P95-100 (Japan Welding Society, issued on February 5, 2004) Tadashi Takemoto and Ryo Sato “High-Reliability Micro Soldering Technology” (published on January 11, 1991, Industrial Research Council, P132-133) Translated by Tadashi Takemoto and Shinichi Naito “Soldering in Electronics” (August 30, 1986, published by Nikkan Kogyo Shimbun, P150-151)

In recent years, ceramic-based packages have become increasingly smaller. Accordingly, it is required to make the width of the Au—Sn alloy solder paste applied for hermetic sealing of the package thinner and narrower. In order to form this thin and narrow Au—Sn alloy solder paste coating film by the stencil printing method, the thickness of the stencil mask is further reduced, and the width of the through-grooves provided in the stencil mask is further reduced. Must. However, the Au-Sn alloy solder paste obtained as the through-thin groove width of the stencil mask becomes narrower is printed in a cut line shape having a non-coated portion, and this Au-Sn alloy solder paste is cut. When the reflow process is performed in a linearly printed state, a portion where the Au—Sn alloy solder is not formed is generated. For example, when the ceramic package is hermetically sealed, a non-joined portion of the Au—Sn alloy solder is generated and sufficient A problem has arisen that it is impossible to maintain a tight airtightness.

Therefore, the present inventors have studied to solve such problems. as a result,
(B) The Au-Sn alloy solder paste is printed intermittently in dotted lines because the Au-Sn alloy solder paste is evenly filled into the through-slots of the stencil mask as the width of the through-slots of the stencil mask is reduced. Without being printed on a cut line having a non-coated portion,
(B) an average particle diameter _{D 50} of the Au-Sn alloy solder powder contained in the conventional Au-Sn alloy solder paste is in the range of 10 to 40 [mu] m, Au-Sn alloy contained in the Au-Sn alloy solder paste the solder powder to finer average particle diameter _{D 50} of and maximum particle size less than 5 [mu] m: and 10μm or less, further Au-Sn alloy solder paste Au-Sn alloy solder viscosity was adjusted to a range of 180~300Pa · s of Even if the width of the through-slot groove of the stencil mask is further narrowed, the paste can be filled evenly in the through-slot, and does not become an intermittent coating layer of the Au-Sn alloy solder paste.
(C) The flux mixed with the fine Au—Sn alloy solder powder having an average particle size D _{50 of} less than 5 μm and a maximum particle size of 10 μm or less is a generally known rosin flux (RMA flux, R flux, RA). Among them, research results such as RA flux being preferable are obtained.

The present invention has been made based on the results of such research,
RA flux: 5.0 to 7.5% by mass, balance of Sn: 15 to 25% by mass, remainder: Au—Sn alloy solder powder having a component composition consisting of Au and inevitable impurities Au—Sn alloy solder paste for printing, wherein the viscosity of the printing Au—Sn alloy solder paste is in the range of 180 to 300 Pa · s, and further included in the Au—Sn alloy solder paste for printing The alloy solder powder is characterized by an Au—Sn alloy solder paste for printing, which is an Au—Sn alloy solder powder having an average particle size of less than 5 μm and a maximum particle size of 10 μm or less.

The Au—Sn alloy solder for printing according to the present invention is produced by the following method. First, by dissolving an Au—Sn alloy having a component composition containing Sn: 15 to 25% by mass and the remainder consisting of Au and inevitable impurities, the obtained molten metal is injected with an inert gas to be gas atomized. -Sn alloy solder powder was produced, and the Au-Sn alloy solder powder thus produced was classified to adjust the particle size, and fine Au-Sn having an average particle size D _{50 of} less than 5 µm and a maximum particle size of 10 µm or less Produces alloy solder powder.

The fine Au—Sn alloy powder thus obtained is mixed with RA flux to prepare an Au—Sn alloy solder paste. At this time, the amount of RA flux blended in the Au—Sn alloy solder powder is blended so as to be in the range of 5.0 to 7.5 mass%, and the viscosity of the Au—Sn alloy solder paste is 180 to 300 Pa · More preferably, it is within the range of s.

Since the component composition of the Au-Sn alloy solder powder contained in the printing Au-Sn alloy solder paste of this invention is in a range generally known as Au-Sn alloy solder, explanation of the reasons for limiting the component composition is omitted. .
The Au—Sn alloy solder powder contained in the printing Au—Sn alloy solder paste of the present invention is limited to the average particle size D ₅₀ : 5 μm or less and the maximum particle size: 10 μm or less. the average particle diameter _{D 50} exceeds the 5 [mu] m, the maximum particle diameter exceeds 10 [mu] m, a thin stencil mask width further narrower and the thickness of the through fine grooves more (e.g., width: 60 to 80 m, thickness: 15 This is because, when stencil printing is performed using 20 μm), intermittent printing partially interrupted is not preferable.
Further, Au—obtained by mixing 5.0 to 7.5% by mass of commercially available RA flux with fine Au—Sn alloy solder powder having an average particle size D _{50 of} 5 μm or less and a maximum particle size of 10 μm or less. Even if it is a Sn alloy solder paste, if the viscosity is less than 180 Pa · s, the viscosity is too low, the plate slippage property at the time of stencil printing is bad, and the paste becomes dull and cheap after the plate slippage. Is more than 300 Pa · s, the viscosity is too high, and it does not have good rolling properties on the stencil, which is not preferable. Therefore, the viscosity of the printing Au—Sn alloy solder paste of the present invention is set in the range of 180 to 300 Pa · s.
The flux contained in the printing Au-Sn alloy solder paste of this invention is limited to the RA flux. The RA flux removes the oxide film on the surface of the Au-Sn alloy powder when the Au-Sn alloy powder is under 5 μm. This is because the effect of melting and agglomerating is remarkable, but the other flux has a weak effect of melting and aggregating by removing the oxide film on the surface of the Au—Sn alloy powder.

  The Au—Sn alloy solder paste according to the present invention does not generate a non-printed portion during printing. Therefore, the reliability of the joint is superior to the conventional Au—Sn alloy solder paste, and the final product is defective. The rate of occurrence can also be reduced to reduce the cost, and an excellent industrial effect can be achieved.

By gas atomizing the Au—Sn alloy solder melt obtained by melting in a high-frequency melting furnace, an Au—Sn alloy solder powder containing Sn: 20% by mass and the balance consisting of Au and inevitable impurities is produced. The Au—Sn alloy solder powder obtained by gas atomization was classified using a classifier, and the particle size distribution of the Au—Sn alloy solder powder obtained by classification was measured using a microtrack (MT3300 manufactured by Nikkiso). Then, Au—Sn alloy solder powders A to G having the average particle diameter D ₅₀ and the maximum particle diameter shown in Table 1 were produced.

Further, commercially available RA flux and RMA flux are prepared, and Au—Sn alloy solder powders A to G having different average particle sizes and maximum particle sizes shown in Table 1 are added to the RA flux and RMA flux in the amounts shown in Table 2. The present invention Au—Sn alloy solder paste (hereinafter referred to as “present paste”) 1 to 6 and the comparative Au—Sn alloy solder paste (hereinafter referred to as “comparative paste”) 1 to 6 having a viscosity shown in Table 2 mixed with RA flux. 3 and a conventional Au—Sn alloy solder paste (hereinafter referred to as a conventional paste) 1 were prepared.

Furthermore, a Kovar plate is prepared, a Ni plating layer (thickness: 5 μm) is formed on the surface of the plate, and an Au plating layer (thickness: 0.1 μm) is further applied to the outermost surface of the Ni plating layer. A substrate was prepared and prepared.
Furthermore, in order to form an Au—Sn alloy solder frame having a package size 1610 (length: 1.6 mm, width: 1.0 mm), a thickness in which 100 frame-shaped through-grooves having a width: 60 μm are provided. : A 15 μm printing stencil mask was prepared.
The stencil mask for printing is placed on the substrate, the pastes 1 to 6 of the present invention, the comparative pastes 1 to 3 and the conventional paste 1 are supplied onto the stencil mask for printing, printed using a substrate printing machine, and printed. After removing the stencil mask, a belt furnace was used, and reflow treatment was performed in a N ₂ atmosphere at a peak temperature of 320 ° C. Since the flux residue remained on the substrate after the reflow treatment, the substrate was cleaned. Measure the average width and average thickness of the short-side midpoint and long-side midpoint of 100 Au-Sn alloy solder frames formed on a substrate using a three-dimensional measuring machine (Nikon NEXIV VMR-3020). Then, the number of Au—Sn alloy solder frames in which the non-formed portion on which the Au—Sn alloy solder was not placed was counted among the 100 Au—Sn alloy solder frames was counted, and the results are shown in Table 2.

From the results shown in Tables 1 and 2, the width and thickness of the Au—Sn alloy solder frame formed on the substrate surface using the comparative pastes 1 to 3 vary widely, and the Au—Sn alloy solder is not on the surface. A formed portion is generated and there is a bonding failure. Further, the conventional paste 1 does not form an Au—Sn alloy solder frame, but an Au—Sn alloy solder powder A to having an average particle size of less than 5 μm and a maximum particle size of 10 μm or less. The width and thickness of the Au—Sn alloy solder frame formed on the substrate surface using the pastes 1 to 6 of the present invention containing F are small in variation, and a non-formed portion on which no Au—Sn alloy solder is placed is generated. From this, it can be seen that the pastes 1 to 6 of the present invention can perform solder bonding with higher reliability than the comparative pastes 1 to 3 and the conventional paste 1.

Claims (1)

RA flux: 5.0 to 7.5% by mass, balance of Sn: 15 to 25% by mass, remainder: Au—Sn alloy solder powder having a component composition consisting of Au and inevitable impurities Au—Sn alloy solder paste for printing, wherein the viscosity of the printing Au—Sn alloy solder paste is in the range of 180 to 300 Pa · s, and further included in the Au—Sn alloy solder paste for printing A printing Au-Sn alloy solder paste, wherein the alloy solder powder is an Au-Sn alloy solder powder having an average particle size of less than 5 m and a maximum particle size of 10 m or less.