JPH0483369A - Lead frame - 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 application of the invention]

The present invention relates to lead frames used in the semiconductor industry, and more particularly to surface treatment of copper alloy lead frame materials.

[Conventional technology]

The copper alloy material used for lead frames includes C194
Although there are many materials such as phosphor bronze material, tin-containing steel material, etc., C194 material is particularly often used. These copper alloy plates are processed into a lead frame shape by stamping or etching, and then subjected to necessary plating treatment. Conventionally, the plating process for these copper alloy lead frames is
After performing an ultra-thin copper strike process of approximately 0.1 μm to 0.3 μm on the entire surface of the lead frame, partial silver is applied only to the pads and lead tips where bonding is required using a high-speed partial plating machine using a jet flow method. Plating was being done. The lead frame plated in this way is subjected to die bonding, wire bonding, and resin molding in one culm of semiconductor assembly, and then solder plating or molten solder is applied to the so-called outer leads that protrude from the mold. A solder layer is formed by the dip, and a semiconductor component with one function is completed. However, lead frames made with such specifications (
For example, in a lead frame made of C194 material that has a copper strike of 0.2 μm on the entire surface and then partial silver plating of 4 μm on the pads and lead tips, if molten solder dip 1 is applied to the outer lead There was a problem with soldering called dewetting, which was prone to defects. Particularly recently, WW rosin-based flux has been replaced with post-cleaning flux from the standpoint of anti-pollution and work safety and hygiene.
Water-soluble fluxes that do not use organic solvents are increasingly being used, and because the surface coverage of water-soluble fluxes is relatively weak, the problem of soldering lead frames has come into focus.

[Problem to be solved by the invention]

An object of the present invention is to provide a lead frame that has good soldering properties even in a molten solder dip process that uses a water-soluble flux with low surface coverage.

[Means to solve the problem]

In the lead frame of the present invention, a copper alloy plate material formed into the shape of a lead frame is plated with bright copper over the entire surface, and copper plating is applied to the portions of the bright steel plating that require bonding. Further, the bright copper plating is deposited from copper bronze (cyan alkali copper), and the thickness of the bright copper plating is in the range of 0.5 μm to 3 μm. When producing a lead frame according to the present invention, a copper alloy plate material formed into the shape of a lead frame is plated with bright copper over the entire surface, and then areas on the bright copper plating that require bonding are plated with silver.

[Effect]

The lead frame of the present invention will be explained according to the drawings. FIG. 1 is a partial plan view showing a 14-bin IC lead frame. Figure 2 shows the A- of the 14-bin IC lead frame in Figure 1.
It is a schematic cross-sectional view taken along A', showing a lead part on the left side and a pad part on the right side. As shown in Figure 1, pad 1 is partially silver plated area 2.
The partial silver plating area 2 is located within the resin mold area 3. One end of the plurality of outer leads 4 is partially silver plated area 2
They are each close to pad 1 within. Pad 1 and outer lead 4 are made of copper alloy material 5. The copper alloy material referred to herein refers to materials that are generally used as lead frame materials, such as C194 material, phosphor bronze material, and soot-containing steel material. In the present invention, as shown in FIG. 2, the entire surface of the copper alloy material 5 is coated with bright copper plating 6. Bright copper plating takes into account that after resin molding, the part where molten solder dip is performed is the outer lead (usually the copper strike surface), and that it is also good as a base plating for partial silver plating on pad 1 etc. It is best to apply this to the entire surface of the lead frame. As a plating bath for obtaining bright copper plating, a plating bath in which potassium thiocyanate is added as a brightening agent to copper cyanide (cyan alkali copper) is preferably used. In general, copper plating baths include bronze bronze baths, copper sulfate baths, copper birophosphate baths, etc.; , a copper bronze plating bath is best. Copper plating films obtained from other baths produce oxide films that are easily peeled off due to thermal history, and may not be usable in semiconductor assembly processes. Therefore, a bronze bronze bath is preferable as a bright copper plating bath. In addition, compared to matte plating, bright plating has a relatively thin plating thickness and good soldering performance, and there is less copper penetration into the molten solder dip bath, resulting in less contamination of the solder bath. There are advantages. The thickness of the bright copper plating varies somewhat depending on the thermal history in the semiconductor assembly process and the conditions of the acid activation treatment performed before molten solder dipping, but even after this process, a bright copper plating film with good solderability remains. It only needs to be at least the remaining minimum condition, and the range is 0.5 μm to 3 μm,
More preferably, it is 1 to 2 μm. If the thickness is less than 0.5 μm, the stability of soldering, which is a feature of the present invention, cannot be obtained, and conversely, even if the thickness exceeds 3 μm, soldering due to an increase in film thickness cannot be expected to improve the soldering properties, so it is unnecessary. This is undesirable because it also causes an increase in manufacturing costs. Bright copper plating is generally said to form layered crystals, and the chemical reactivity of the metal surface is said to be low. It is known that when a steel material is placed in a molten solder dip bath, an intermediate metal layer of copper and soot is first formed on its surface.
In the case of bright copper plating, the thickness is relatively thin, and as a result, an inactive lead-rich layer is not formed on the outside of the steel-tin intermediate metal layer, and it is presumed that good soldering is achieved. Ta. In the present invention, after performing bright copper plating as described above,
Partial silver plating 7 is applied to the pad 1 and the tip portion of the outer lead 4 adjacent to the pad 1. Selective silver plating is performed using high-speed partial plating equipment using a jet flow method, only on the areas required for die bonding and wire bonding, but these selective silver plating areas are usually inside the resin mold area and are directly It has nothing to do with soldering.

【Example】

[Example 1 10 g'/l of potassium thiocyanate as a brightening agent was added to a copper cyanide plating bath having Bog/l as copper (introduced as cupric cyanide) and 5 g/l as free N, Ottm, 0.5 was applied to a C194 material test piece under the conditions of bath temperature 70 °C and cathode current density 7 A/d m'.
Bright copper plating was performed to thicknesses of μm, 1 μm, 2 μm, and 3 czm. The test piece with bright copper plating was heated to 6 at 170℃.
Heating was carried out in air for an hour. The generated oxide film is
After cleaning with a pickling solution consisting of % sulfuric acid and 15% nitric acid for 10 seconds at room temperature, immersion in water-soluble flux (manufactured by Alpha Metals: #2668F) for 5 seconds, and then in a molten solder dip bath (270℃) for 5 seconds. It was soaked and the soldering properties were evaluated. Those with bright steel plating of 0 μm (C194 material side) caused a large amount of dewetting, but those with bright copper plating of 0.5 μm or more showed good soldering properties and no dewetting. Not observed. [Example 2] A pre-bright copper plating bath was prepared which was the same as in Example 1 except that 1.5 mg/e of selenium (Se 2 ) was added as a brightener in the form of potassium selenium cyanide. OAzm, 0.5μ was applied to a test piece made of 0194 material under the conditions of bath temperature 70℃ and cathode current density 14A/dm2.
Bright copper plating was carried out to a thickness of m, 1 μm, 2 μm, and 3 μm, heated under the same conditions as in Example 1, and a soldering test was conducted. The results were exactly the same as in Example 1, with bright copper plating of 0.5μ
If soldering was carried out for more than m, good soldering was not achieved. [Comparative Example 1] A comparative test was conducted on a test piece made of C194 material, which was subjected to copper strike without being subjected to bright copper plating. In other words, there was no copper strike on the C194 material test piece.
．． A soldering test was carried out by heating under the same conditions as in Example 1. [Comparative Example 2] A comparative test was conducted in which a C194 test piece was plated with matte copper without being plated with bright copper. I did it. That is, a test piece made of C194 material was plated with matte steel to a thickness of 0.5 μm, heated under the same conditions as in Example 1, and
A soldering test was conducted. The plate in which the matte steel plating was applied to a thickness of 0.5 μm was better than Comparative Example 1, that is, the plate in which the copper strike was applied to a thickness of 0.2 μm, but slight dewetting was observed. From the above results, it can be seen that bright copper plating greatly contributes to improving soldering properties.

【Effect of the invention】

By using a lead frame with good soldering properties according to the present invention, it becomes possible to supply highly reliable semiconductor components through an inexpensive molten solder dip process without going through an expensive solder plating process.

[Brief explanation of the drawing]

FIG. 1 is a partial plan view showing a 14-pin IC lead frame. Figure 2 shows the A- of the 14-bin IC lead frame in Figure 1.
It is a schematic sectional view along A-. (Left space on this page) In the figure, reference numbers indicate the following elements. ...pad, ...partial silver plating area, ...resin mold area, ...outer lead, ...copper alloy material, ...full bright copper plating, ...partial silver plating.

Claims (2)

[Claims] (1) Copper alloy plate material formed into lead frame shape,
A lead frame characterized in that the entire surface is coated with bright copper plating, and the portions of the bright copper plating that require bonding are coated with copper. (2) The bright copper plating is deposited from copper bronze (cyan alkali copper), and the thickness of the bright copper plating is in the range of 0.5 μm to 3 μm. Lead frame listed.