JPS62123754A - Rinsing method of lead frame - Google Patents

Abstract

PURPOSE:To prevent an oxidizing film from being generated by oxidation due to remaining water, by performing natural evaporation in which a surface water on a lead frame is gradually evaporated with water-substitution agent and freon soakage. CONSTITUTION:Etching resist is completely removed from a lead frame surface, and following a water-rinsing process 1 of the lead frame, a process 2, in which the lead frame is soaked with alcohol or water-substitution agent liquid such as interface activator liquid, is performed. And, a process 3, in which the lead frame is soaked with freon liquid, is performed to substitute rapid-drying freon for the water-substitution agent on the lead frame surface. After a freon liquid- soakage process 3, the lead frame is placed in a pure freon vapor, to perform a freon-vaporizing process 4. Then, the lead frame is placed in a temperature state below atmospheric temperature through a natural cooling process 5, of the lead frame, to raise its temperature to a degree of atmospheric temperature and to draw out it to the atmosphere. Thus, the lead frame surface is prevented from being dewed.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention particularly relates to a method for cleaning lead frames which are metal-deposited by vapor phase treatment.

(Conventional technology) Lead frame (iron/nickel alloy) by etching process
When a pattern of is formed.

<Problems to be Solved by the Invention> As described above, in the conventional method of removing the etching resist and drying the washed lead frame by blowing hot air or warm air, the etching resist is removed and the water on the lead frame is dried by blowing hot air. Water droplets from washing remain on the area, delaying drying of the area and forming a thin oxide film. When a metal layer is formed in a vapor phase process such as vacuum evaporation on a part of such a lead frame where an oxide film has been formed in a subsequent process, that part becomes discolored in the form of white dots.
In the process of IC ceramic packages that require high reliability, this has caused defects such as poor adhesion or uneven adhesion of bonding wires.

If the oxidation of the lead frame is more severe, the oxidized portion will turn yellow and cause so-called complete rust. If vapor phase treatment is applied on top of that, the contact strength of the vapor-deposited metal layer will decrease, causing it to peel off.
This caused more serious defects such as foaming. For this reason,
By immersing the washed lead frame in a drying liquid (old-time experts say, a mixture of Freon and alcohol [for example, Magic Dry (product name)] and drying it, the formation of an oxide film due to the delay in drying of water droplets can be prevented. In the case of high-quality ceramic packages, even after being treated with the darning process, product defects due to uneven drying of moisture were discovered, and the product was not perfect.

The present invention has been made in view of the problems of the prior art, and it is an object of the present invention to provide a lead frame cleaning method that can completely remove moisture in a pre-process of an etching lead frame which is subjected to gas phase treatment in a subsequent process. It is something.

<Means for Solving the Problems> The procedure of the lead frame cleaning method according to the present invention that achieves the above object is to perform the above-mentioned steps prior to the step of forming a metal layer by vapor phase treatment on the lead frame formed by etching treatment. Following the step of removing the etching resist of the lead frame and washing it with water, the step of immersing the washed lead frame in a water displacing agent solution, and the step of immersing it in Freon,
It is characterized by sequentially performing a Freon method air drying step and a step of drying Freon in a low temperature environment below atmospheric temperature. Further, in this case, it is preferable to use a so-called wet processing method in which the surface of the lead frame is kept dry between successive steps.

Furthermore, if there is a lot of moisture on the lead frame that has been washed with water after removing the etching resist, use a water-absorbent roll to dry the lead frame before the above lead frame cleaning method in order to reduce the amount of moisture carried into the subsequent process. It is characterized by applying a draining process to absorb and remove moisture from the surface of the wafer.

<Embodiment> An embodiment of a lead frame cleaning method according to the invention will be described with reference to the drawings.

FIG. 1 is a process diagram of an embodiment of the lead frame cleaning method according to the present invention. The lead frame cleaning method according to the present invention involves etching and etching from the surface of the lead frame, which has been formed into a specific pattern by etching, prior to the step of later forming an aluminum layer by vapor phase treatment such as vacuum evaporation. After completely removing the resist, the lead frame is washed with water (step 1), followed by step 2 of immersing the lead frame wet with water in water displacing agent liquid such as alcohol or surfactant liquid. The moisture on the surface of the lead frame is dissolved into the moisture displacing agent. Next, step 3 is performed in which the lead frame is immersed in a Freon liquid, and the moisture displacing agent on the surface of the lead frame is replaced with Freon, which dries quickly. However, if the lead frame is simply air-dried after immersion in Freon, moisture in the atmosphere will condense on the surface of the lead frame due to the latent heat of vaporization of Freon in the atmosphere, and the lead frame will suffer from the negative effects of moisture oxidation. Also, even when drying with hot air, uneven drying occurs.

For this reason, after the Freon liquid immersion step 3, the lead frame is placed in pure Freon vapor, and the Freon vapor leaving step 4 is performed. Next, through step 5, the lead frame is naturally cooled by placing it in an environment at a temperature below atmospheric temperature, for example, below 10°C.
By raising the lead frame slightly to the atmospheric temperature and taking it out into the atmosphere, there is no fear of dew condensation forming on the lead frame surface. In this way, a lead frame is obtained in which the moisture that adhered to the lead frame in the water washing step 1 is completely removed. Therefore, unlike in the conventional case, when a lead frame that has been washed with water and is dried with hot air, a thin oxide film is not formed due to remaining moisture, which will not cause any adverse effects in the subsequent gas phase treatment process.

Even if the water was dried by immersing it in a drying liquid after washing with water in order to thoroughly remove water, product defects still occurred due to uneven drying of the water.However, according to the method of the present invention, the remaining water from washing with water can be removed. can completely eliminate the influence of
We were able to provide a clean lead frame. by this.

In the later IC processing process, even if an aluminum layer etc. is applied by vapor phase treatment and then a bonding process is performed using a bonding wire, a uniform bonding force of wire bonding can be obtained, and particularly high reliability is required. We succeeded in significantly increasing the reliability of ceramic packaged ICs for VLSI.

In the method of the present invention, if the lead frame is highly resistant to moisture in the lead frame washing step 1, in order to reduce the moisture carried into the subsequent process, the lead frame is washed with water absorbent rolls such as sponge rolls. In the embodiment of the present invention shown in FIG. 2, in which draining is preferably carried out, between the water washing step 1 and the water displacing agent solution immersion step 2 in the embodiment shown in FIG. Two absorbent rolls such as sponges 81+8□
The lead frame 7 is passed through the lead frame 7.
Draining step 6 using a water-absorbent roll to drain the surface of the
It has been established. In FIG. 2, steps with the same reference numbers as those shown in FIG. 1 are the same steps.

What is important about the lead frame cleaning method according to the present invention is that
In each process, the lead frames must be separated and processed one by one.

If there is a portion of the lead frame that overlaps each other and is subjected to machining, the treatment liquid from the previous step and the treatment liquid from the subsequent step will not be replaced well in the overlapped portion, resulting in residual liquid from the previous step. This is due to the difference in surface tension of each liquid and the limit of permeability. Furthermore, what is important about the method of the present invention is that up to the final steam drying step 5, the lead frame surface must be moved to the next step while being moistened by the immersion liquid between steps. be. It must be processed using wet processing methods, in no case creating dry conditions.

FIG. 4 shows a configuration diagram of an apparatus for carrying out the lead frame cleaning method according to the present invention shown in FIG. 1 or 2.

According to the lead frame cleaning method according to the present invention shown in FIG. 1 or FIG. Moved to 1. In the washing step 1, the strip-shaped lead frame is continuously washed in water 10, and then transferred to the next step. If there is not much moisture adhesion in the washing step, the step is directly immersed in the water displacing agent liquid 12 (Step 2). In step 2, moisture on the surface of the lead frame 7 is dissolved in a moisture displacing agent 12°, such as alcohol or a surfactant liquid. still,
When the water displacing agent 12 is alcohol 14, it is heated in an adjacent water separation tank 13 by utilizing the boiling point difference between water and alcohol, and only the alcohol in the tank is evaporated and recovered, and the water is drained. In this way, the water content of the water displacement agent liquid 12 can be kept constant. Next, the lead frame 7 is transferred to a Freon dipping step 3. In the Freon dipping step 3, the moisture displacing agent liquid on the surface of the lead frame 7 is replaced with the fast-drying Freon 1.
Replace with 5. Although the Freon tank is divided into two, 91 and 82, the second Freon tank 92 is kept at a lower temperature than the first Freon tank 9. This is the Freon-wet lead frame 7 in preparation for the next Freon steam drying.
This is because when the temperature of the lead frame is lowered and the lead frame is moved to an environment of Freon vapor near the Freon boiling point, Freon gas often condenses on the lead frame, increasing the cleaning effect of Freon vapor.

The lead frame 7 is made of freon g from the freon dipping process 3.
The lead frame is then moved to an air drying step 4, where the surface of the lead frame is cleaned with pure Freon vapor 16. The lead frame 7 is then gradually lifted upward and transferred to a low-temperature drying step 5 in a cooling zone cooled by cooling vibes 17 around the lead frame 7. Here, due to the low temperature, the Freon is liquefied and recovered, the temperature of the lead frame 7 is also lowered, and after waiting for the Freon to dry naturally, it is further gradually moved upward to bring the temperature of the lead frame 7 to a level equal to room temperature. Therefore, the surface of the lead frame 7 is cleaned and cleaned with Freon steam without condensation of moisture in the atmosphere, and the lead frame 7 is taken out into the atmosphere without any oxidation due to moisture. Obtainable.

In addition, in the lead frame cleaning method according to the present invention, the lead frame is formed into a strip or a strip, and the lead frame is placed in a frame basket 1.
1 may be batch processed.

<Effects of the Invention> The lead frame cleaning method according to the present invention removes the surface moisture of a washed lead frame by replacing it with a water displacing agent liquid, and then immersing the lead frame in Freon to replace the moisture displacing agent liquid with Freon, which dries quickly. A Freon dipping process is performed to gradually naturally evaporate the Freon component from the surface of the lead frame, bringing it to atmospheric temperature and taking it out into the atmosphere. Therefore,
When taken out into the atmosphere, there is no Freon component on the surface of the lead frame, so there is no condensation of moisture in the atmosphere due to cooling of the lead frame due to the vaporization of Freon. No oxide film is formed due to oxidation of the IC ceramic package, no metal layer is formed by vapor phase treatment in the post-process of the IC ceramic package, and no deterioration in the bonding strength of the wipe bonding applied there is observed.
In particular, we were able to significantly improve the reliability of ceramic packages for VLSIs, which require high reliability.

[Brief explanation of drawings]

Fig. 1 is a process diagram of one embodiment of the lead frame cleaning method according to the present invention, Fig. 2 is a process diagram of another embodiment of the present invention, and Fig. 3 is a water absorbent roll used in the process shown in Fig. 2. FIG. 4 is an explanatory diagram of an apparatus for carrying out a draining process. FIG. 4 is a configuration diagram of an apparatus for carrying out the method of the embodiment shown in FIG. 1 or 2. In the drawing, 1 is a water washing process, and 2 is a water displacing agent solution immersion process. 3 is Freon soaking process, 4 is Freon steam drying process, 5 is
is a low temperature drying process, 6 is a water absorbent roll draining process, 7 is a lead frame, 8182 is a water absorbent roll, 8□, 9□ are freon liquid j4.10 is water, 11 is a frame basket, 12
13 is a water displacement agent liquid, 13 is a water separation tank, 14 is alcohol, 15 is Freon, 16 is Freon vapor, and 17 is a cooling pipe.

Claims (5)

[Claims] (1) Prior to the step of forming a metal layer by vapor phase treatment on the lead frame formed by etching, the etching resist of the lead frame is removed and washed with water, and then the washed lead frame is separated at intervals. A method for cleaning a lead frame, characterized by sequentially performing a step of immersing the lead frame in a water displacing agent solution at a distance, a step of immersing it in Freon, a Freon vapor drying step, and a step of drying in a low-temperature environment. (2) The lead frame cleaning method according to claim 1, wherein the lead frame surface is kept wet during the continuous steps. (3) The lead frame cleaning method according to claim 1, wherein the moisture displacing agent is alcohol or a surfactant liquid. (4) Prior to the process of forming a metal layer by vapor phase treatment, the etching resist of the lead frame formed by etching process is removed, and following the process of washing with water, the amount of moisture removed from the lead frame using a water-absorbing roll. A lead frame characterized in that the lead frame is sequentially subjected to a draining step for reducing the water content, a step of immersing the lead frame in a water displacing agent solution, a step of immersing it in Freon, a Freon vapor drying step, and a step of drying in a low temperature environment. Cleaning method. (5) The lead frame cleaning method according to claim 4, wherein the surface of the lead frame is kept wet during the continuous steps.