JPH08158069A - Working of finely etched product - Google Patents

Abstract

PURPOSE: To conduct smooth etching excellent in sectional form by spray-etching an Ni alloy sheet with an aq. ferric chloride soln. to form a through-hole and then dipping the etched sheet in a specified aq. ferric chloride soln. contg. Ni, Cr and FeCl2 . CONSTITUTION: An Ni alloy sheet to be worked on which a photoresist is applied in a specified pattern is transported, and an aq. ferric chloride soln. is sprayed on the surface, which is etched. When the through-hole has been formed as shown in D, spraying is stopped. The sheet is then dipped in a >=45 deg.- Baume aq. ferric chloride soln. kept at >=30 deg.C and contg. <=0.6wt.% Ni, <=0.6% Cr and <=30% FeCl2 to preferentially dissolve off the projected unetched part. Consequently, an excellent etched sectional form and a smoothly etched surface excellent in dimensional accuracy are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a product such as a lead frame of an integrated circuit device or a micro electronic component, which requires high accuracy, by etching.

[0002]

2. Description of the Related Art Most of lead frames made of Fe-42Ni alloy for electrically connecting a highly integrated circuit and an external circuit are manufactured by etching using an aqueous solution of ferric chloride.

In the dawn of etching, an etching method of immersing in an etching solution was adopted.
Currently, a spray etching process is generally performed, which has a high etching rate, high productivity, and an excellent etching factor (etching depth / side etching amount).

The spray etching process is a method in which a part of the surface of the material to be processed is covered with a corrosion resistant resist, and a ferric chloride aqueous solution is sprayed to selectively dissolve the exposed metal portion to form a target shape.

Due to the rapid integration of circuit elements in recent years,
The required processing accuracy has become extremely high, and even slight dimensional fluctuations have become unacceptable. For example, due to the high integration, the spacing between the lead pins in the inner lead of the lead frame becomes extremely narrow, and if there is an etching residue on the etching processed cross section, the lead pin is only bent a little and comes into contact with the adjacent pin, resulting in a defective product.

Further, when the etching cross section is rough, there arises a problem that dirt easily adheres, so that a smooth processed surface is required.

However, in the spray etching method which is excellent in etching rate and etching factor, it is difficult to finely adjust the etching amount due to the high etching rate, there is little etching residue, and the target product width is stably obtained. Is difficult. Further, the spray etching method has a drawback that the etching surface becomes rough and rough. On the other hand, in the dipping etching processing method capable of obtaining a smooth etching surface, although the etching rate is slow, the etching amount can be finely adjusted, but the productivity is low and the etching factor is also poor.

Japanese Unexamined Patent Publication No. 4-263085 discloses a method of freely obtaining a smooth etching surface and a rough etching surface by controlling the temperature of the etching solution and the FeCl ₃ concentration in the spray etching method. , This method works only for stainless steel.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and provides an etching processing method which is excellent in etching cross-sectional shape and has a small dimensional variation and a smooth etching surface. With the goal.

[0010]

Therefore, the present inventor has studied and studied in detail the process of changing the cross-sectional shape of the material to be processed due to the etching in order to solve the above problems, and as a result, found that a high etching factor of the spray etching process was found. Use
The intermediate product is produced in a short time, and then it is immersed in an aqueous solution of ferric chloride with a controlled content of impurities Ni, Cr, and FeCl _{2 at} a low temperature, and etching is performed to reduce the etching residue, and The present invention has been completed based on the finding that it is possible to stably manufacture a product having a smooth etching cross section and a target product width.

The gist of the present invention is that in a spray etching method for carrying out etching by spraying an aqueous solution of ferric chloride onto the surface of a Ni alloy plate as a workpiece to be processed, When the material has a through hole, spray etching is stopped, then the liquid temperature is 30 ° C or less, the concentration is 45 Baume or more, and the weight% is
"Processing method for finely-etched products characterized by natural immersion in an aqueous solution of ferric chloride containing 0.6% or less of Ni, 0.6% or less of Cr and 3.0% or less of FeCl _2. "

[0012]

Next, the reason and function of limiting the processing conditions of the present invention will be described.

(1) Discontinuation of Spray Etching and Immersion Etching FIG. 1 is a diagram showing the progress of corrosion of a workpiece in spray etching. The target hole or groove is formed through the process shown by A → F in FIG.

In a lead frame having a large number of lead pins used as a part of a central processing element for a computer recently, the distance between the lead pins is extremely narrow due to its high degree of integration. Therefore, as described above, when the etching residue as shown in FIG. 1D exists, the lead pin comes into contact with the adjacent pin due to a slight bending or the like, resulting in a defective product.

On the other hand, a wide lead pin width is required in order to stabilize the wire connection for connecting the tip of the inner lead and the integrated circuit and reduce the electric resistance in the lead frame.

Therefore, if the etching time is shortened to secure a wide lead pin width, the etching residue becomes large, and if the etching time is lengthened to remove the etching residue, the lead pin width becomes narrow.

Although the spray etching is excellent in the etching factor (etching depth / side etching amount), the etching rate is too fast, and it is difficult to finely adjust the etching amount.
The lead pin width is often narrower than the target product width.
Therefore, in the spray etching processing, the processing is performed at high speed until a through hole is formed in the material to be processed, that is, up to D in FIG. 1, and then the material is immersed in an aqueous solution of ferric chloride to accurately dissolve and remove the etching residue.

FIG. 1D shows a shape in which the etching residue is projected. When immersed in a stationary solution,
Since the dissolution of the metal proceeds uniformly at the contact interface between the solution and the metal, the protruding portion in the solution has a long metal / solution interface per unit volume, and thus the protruding portion is preferential. The etching residue disappears with the lead pin width narrowed. Although the etching rate is slow in the immersion state, only the remaining portion of the etching dissolves, it does not take so long, and the etching rate is slow, so the control of the etching amount is simple.

(2) Immersion Etching Solution Immersion etching is carried out to remove the unmelted residue after spray etching and to make the etching surface smooth, and use a concentrated ferric chloride aqueous solution at a low temperature with almost no impurities. By this, a more complete diffusion rate control is established in the immersion state, and as a result, an extremely smooth etching surface is obtained.

(A) Etching solution temperature temperature When the etching solution temperature exceeds 30 ° C., corrosion progresses too fast, which makes it difficult to control a small amount of etching and the etching end face becomes rough. did. The lower limit is not limited, but if the temperature is too low, the corrosion rate becomes slow, which is not preferable in terms of productivity. A preferable temperature range is 20 to 30 ° C.

(B) Concentration of etching solution The concentration of the etching solution is set to 45 baume or more because a smooth etching surface cannot be obtained if the etching solution concentration is less than 45 baume. Although the upper limit is not limited, the higher the concentration, the slower the etching rate, so about 50 Baume is preferable.

(C) Impurity amount Ni, Cr: Ni and Cr in the impurities have an adverse effect of roughening the etching surface, so the upper limits must be restricted to 0.6% respectively.

FeCl ₂ : FeCl ₂ is generated due to the etching reaction, and if it exceeds 3%, the etching rate becomes slow and the etching surface becomes rough, which is not preferable. Therefore, the upper limit is set to 3%.

(3) Ni alloy The reason why the work material is Ni alloy is that F is used for the lead frame.
Since the e-42Ni alloy is frequently used, the above conditions of the etching solution can be applied when Ni is contained in an amount of 30 to 50%.

[0025]

【Example】

(Embodiment 1) FIG. 2 is an etching line used for carrying out the present invention. A spray etching chamber 1 for spraying an aqueous ferric chloride solution, which is an etching liquid, onto the surface of the workpiece 3 is followed by several washing spray chambers 2 for cleaning. A plurality of stages of spray pipes and spray nozzles 4 are formed on the surface of the workpiece to be continuously sent to the etching spray chamber 1 after finishing the pretreatment.
After the etching solution is sprayed to perform sequential etching, the material to be etched is sprayed with water from the water spray nozzle 5 to be washed in the subsequent several stages of the spray chamber 2, and the progress of the etching is once stopped. After that, the etching condition is grasped by the dimension measuring sensor provided on the outlet side of the water spray chamber 2, and then the material to be processed is conveyed into the immersion etching chamber to perform the immersion etching.

Using this etching line, Fe-42N
A 128-pin lead frame made of i alloy was prepared. The length of the chamber for spray etching is 8 m, and the length of the chamber for immersion etching is 4 m.

FIG. 3 shows a resist pattern of the lead frame. Etching material is 500 x 600 x 0.15mm
Then, as shown in FIG. 3, a resist pattern of 48 lead frames is formed on one processing material (one lead frame having 128 lead pins is etched in one pattern). Be done).

The etching material is inserted from the left side of FIG. 2 and is first processed by spray etching. The line speed was controlled so that the finish at this time was about the same as D in FIG. The spray etching solution used is 55
This is an aqueous ferric chloride solution at 50 ° C at 50 ° C.

The material in the D state by spray etching was subjected to immersion etching in an immersion etching chamber with various changes in the temperature, concentration and impurity content of the etching solution as shown in Table 1.

[0030]

[Table 1]

A resist pattern for dimension measurement was formed at the lower left of the processed material so that the progress of etching could be measured online.

FIG. 4 shows an outline of the cross-sectional shape of the resist pattern for dimension measurement after etching and a dimension measurement site.

The width a of the resist pattern portion for measuring the dimension of the material coming out of the spray etching chamber is automatically measured by the dimension measuring sensor provided on the exit side of the etching chamber, and the etching residue is left based on the result. The material passing speed, that is, the immersion etching time, was determined by the following formula (1) previously obtained for each immersion etching solution so that

T = (ab) × Z ........... (1) t: Immersion etching time (min.) A: Dimension measurement width (μm) b: Photoresist width (μm) (= 130 μm) Z: Coefficient depending on immersion etching solution In Table 1, the coefficient Z of immersion etching time in each immersion etching solution and the average immersion etching time are shown together.

FIG. 5 is a perspective view of the lead pins of the lead frame after the etching is completed. The lead pin flat width (c) and the etching residual width (d) at a portion 300 μm from the tip of the inner lead of the lead pin were measured, and the standard deviation of the lead pin flat width was calculated. The results are shown in Table 1.
Shown in The dimensions shown in the table are average values of 512 randomly selected lead pins, and the dimensional standard of the lead pin flat width is 128 ± 20 μm.

The etched surface was qualitatively observed with a scanning electron microscope. The survey results are also shown in Table 1. Since the etching-dissolved end surface of the lead pin has extremely fine irregularities and ordinary roughness cannot be measured, the observation results are shown in order of smoothness from ⊚ → ○ → Δ → ×.

As a conventional example, etching was performed to the state of F in FIG. 1 only by spray etching, and the surface roughness was observed by the above method, and the residual etching amount and the average and standard deviation of the lead pin flat width were measured. , Table 1
Are also shown.

As is clear from Table 1, in the examples of the present invention, smooth etching end faces were obtained by immersion etching, whereas in the comparative examples and the conventional examples, rough etching end faces were observed.

Further, in the present invention example and the comparative example, even if the etching residue is etched to 1.2 μm or less, the lead flat width is 127.9 μm or more, whereas in the conventional example, it is 125.5 μm. The average value is smaller than the standard median value.

Further, while the standard deviation of the lead flat width is 4.7 in the conventional example by only the spray etching, the standard deviation of the lead pin width is 3.9 at the maximum in the example of the present invention, and the dimensional fluctuation is reduced. Therefore, it can be seen that uniform products can be stably produced.

Therefore, only the product according to the method of the present invention has a smooth etching end surface and the etching residue is 1.2 μm.
Even if the etching process is performed as follows,
It can be seen that the lead flat width of 7.9 μm or more is stably secured.

[0042]

According to the method of the present invention, after the ordinary spray etching, by immersing in the etching solution specified in the present invention, it is possible to almost eliminate the etching residue while securing a wide lead pin width and to smooth the surface. A highly etched surface can be obtained, and highly accurate etching processing becomes possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a progressing process of corrosion of a material to be processed by spray etching.

FIG. 2 is a diagram showing an etching line for carrying out the present invention.

FIG. 3 is a diagram showing a resist pattern of a lead frame.

FIG. 4 is a diagram showing a cross-sectional shape of a dimension measuring resist pattern after etching.

FIG. 5 is a perspective view of a lead pin after etching.

[Explanation of symbols]

 1 Spray Etching Chamber 2 Rinsing Spray Chamber 3 Workpiece Material 4 Spray Pipe and Spray Nozzle

Claims (1)

[Claims] 1. A spray etching method in which a ferric chloride aqueous solution is sprayed onto the surface of a Ni alloy plate to be processed while the Ni alloy plate is being processed, and a through hole is formed in the material by spray etching. Then, spray etching was stopped, and then the ferric chloride aqueous solution with a liquid temperature of 30 ° C. or less, a concentration of 45 Baume or more, and 0.6% or less of Ni by weight%, 0.6% or less of Cr, and 3.0% or less of FeCl ₂ A method for processing a fine etching product, which comprises immersing the product in the inside.