JPH0129875B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is for etching circuit boards etc., which have a reaction chamber, an air supply pipe, an exhaust pipe and electrodes between which the circuit board to be treated can be placed. Regarding plasma reactors for.

Each layer of circuit board often has thousands of connection holes. These holes must be copper plated after drilling, but organic contaminants are generated during drilling and must be removed prior to plating to ensure a fault-free connection.
In order to remove these stains, it is known to clean circuit boards using gas plasma. For this purpose, a gas mixture, namely oxygen and tetrafluoromethane, is introduced into a reaction chamber in which a circuit board is placed between the electrodes, where the electrodes are ionized by means of a high-frequency voltage and the components of the plasma (electrons, ions, free radicals) remove impurities.

PRIOR ART Known reactors for this purpose (U.S. Pat.
No. 4289598) has a horizontal reaction chamber with an annular cross section and hermetically closed on one side by a door covering the entire cross section. Rod-shaped or plate-shaped electrodes are arranged parallel to each other in the room, and the electrodes are alternately connected to both poles of a high-frequency power source. The circuit boards to be treated can be inserted by suspending them in a suitable manner so that each circuit board is placed between electrodes with opposite polarity. A reactant gas supply pipe leads to three or more outlets in the chamber. The air outlet faces into a buttful plate for more uniform airflow.

Problems to be Solved by the Invention However, in the known reaction chamber, although a baffle plate is provided for the inflowing gas, the uniformity of the plasma is insufficient, and turbulence and gas flow velocity around the circuit board are insufficient. Due to the difference, the removal rate of impurities becomes non-uniform.

In plasma etching of very small parts, electrodes of porous material are used, through which gas is allowed to flow, thereby obtaining a more uniform air flow (German patent publications DE-OS 3119742 and DE-OS 3140675). It is known. Apart from the fact that this solution is applicable only to small parts, the problem arises that deformation of the electrode changes the airflow distribution since the electrode also serves as a gas outlet. It is completely impossible to use this for cleaning circuit boards due to the large number of electrodes and the large area to be cleaned.

The aim of the invention is to provide a plasma reactor capable of being uniform and highly efficient even for large workpieces.

Means for solving the problem This object is achieved by a plasma reactor of the type described below. In the present invention, a frit (a gas-permeable layer) is used for supplying gas, and it is preferable to place it on the upper surface of the reaction chamber. Twisted and covered.

The present invention provides a uniform, laminar air flow over the entire cross-section of the reactor used, making it possible to shorten processing times and uniformly remove impurities on the circuit board.

Another advantageous embodiment of the invention is characterized in that the frit supports its own weight and is supported at its edges on the walls of the reaction chamber.

However, considering the different pressures on both sides of the frit, it is also conceivable that the frit rests with its edges on a perforated plate supported on the walls of the reaction chamber. After the airflow passes through the frit, the gas flow rate and pressure are reduced to the lower values typical in the reaction chamber;
This additional use of perforated plates has little effect on the uniformity of the gas supply.

If the thickness of the frit is varied over the length and width of the reactor, imbalances within the reaction chamber can be compensated for. For example, when using a frit with a uniform thickness and inhaling gas from the center, the flow velocity distribution is generally not uniform over the entire cross section. This can be avoided by varying the thickness of the frit within the cross-section of the reactor, for example increasing from the edge to the middle of the reaction chamber and decreasing towards the other edge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention and its additional advantages and features will now be explained in detail by means of embodiments illustrated in the figures. According to FIG. 1, the present plasma reactor has a reaction chamber 1 surrounded by a pressure-resistant wall 2. As shown in FIG. This wall is open at the top of the reaction chamber and has a shoulder 3 on its edge on which a perforated plate 4 rests;
The perforated plate is made of a material such as iron and has a large number of holes 5. A gas-permeable layer, the frit 6, rests on the perforated plate 4, said frit 6 being made of an air-permeable sintered material, such as ceramics, for example. The frit 6 may also consist of a suitable, optionally compacted coarse material. The perforated plate 4 and the frit 6 are covered at their tops by an airtight hood 7, which has an air supply pipe 8 on its upper surface. The hood 7 is sealed between the walls 2 of the reaction chamber 1 and is joined by conventional methods, such as screws, which are only shown here.

On the lower surface of the reaction chamber 1 there is one or preferably several gas outlets (not shown) on the wall 2 of the reaction chamber, which are connected to an exhaust pipe 9 . A vacuum pump 10 is connected to the exhaust pipe 9. Several rows of electrodes 11 (U.S. Pat. No. 4,289,598
) extends along the reaction chamber. Electrode 1
1 are suspended in an insulated state and are alternately connected to both poles of a high frequency power source 12. A circuit board 13 to be treated can be inserted between the electrodes 11, said circuit board being located equidistant from the adjacent electrodes on the left and right. The circuit board 13 is
In order to clarify the loading or unloading of the reaction chamber 1, it can also be suspended in a mounting support movable along a track (not shown) provided in the upper part of the reaction chamber 1. How to hang a circuit board
For example, it is described in US Pat. No. 4,289,598.

FIG. 2 shows that the perforated plate 4 is sealed between the shoulder 3 of the container wall 2 by a seal 14. The hood 7 sealing the top of the reaction chamber is also sealed between the wall 2 by a seal 15. If a sufficiently strong frit 6 is used, the perforated plate 4 can be omitted, in which case the frit 6 supports its own weight and its edges are supported, for example, on shoulders 3 of the container wall 2. At this time, the frit 6 absorbs the difference in air pressure between the inside and outside (external pressure is about 3.5 bar, internal pressure is about 10 ^-4 bar).

Another gain obtained with the present invention is illustrated by FIGS. 3 and 4. A substantially uniform airflow flows out of the frit 6, but this airflow is considerably influenced by the positional relationship of the reaction chamber, electrodes, suspended circuit board, etc. In particular, the flow velocity distribution diagram indicated by the arrows shows that the velocity of the airflow often decreases as it approaches the wall of the container. In the latter case, the flow velocity distribution can be made more uniform by using a frit 6 whose thickness decreases towards the edge, as shown in FIG. However, other non-uniformities in the flow velocity distribution can also be compensated for by appropriate shaping of the frit 6. In a simpler case,
The required shape can be calculated based on fluid mechanics or determined by testing.

The present invention can of course be used with reactors of other shapes, such as vertical ones or those with different cross-sections. The frit also does not necessarily have to be on the top of the reaction chamber. However, it must necessarily extend sufficiently over the entire length and width of the reaction chamber, i.e. it must cover the entire occupied space within the reaction chamber, as seen from the direction of the air flow.

Effects of the Invention With the present invention, a large number of large circuit boards, each measuring one square meter, can be processed quickly and uniformly in large quantities. Further, the present invention has the advantage of providing a uniform distribution of gas and plasma, and therefore can be used not only for plasma etching of circuit boards but also for plasma processing of other workpieces.

[Brief explanation of drawings]

1 is a partially sectional perspective view of a plasma reactor according to the invention, FIG. 2 is an enlarged sectional view of the arrangement of the frits on a perforated plate with a cover hood at the edge, and FIGS. 3 and 4 are different. FIG. 3 is a schematic lateral cross-sectional view of the air flow through a reaction chamber with a frit shape;

Claims (1)

[Scope of Claims] 1 Consists of a reaction chamber, an air supply pipe, an exhaust pipe, and an electrode between which a circuit board to be treated can be placed, preferably on the upper surface of the reaction chamber 1 for gas supply. For etching a circuit board, etc., the frit 6 is sufficiently spread over the entire length and width of the reaction chamber, and the outside thereof is covered by an airtight hood 7. plasma reactor. 2. The plasma reactor according to claim 1, wherein the frit 6 supports its own weight and its edge is supported by the wall 2 of the reaction chamber 1. 3. The plasma reactor according to claim 1, wherein the frit 6 is mounted on a perforated plate whose edges are supported on the wall 2 of the reaction chamber 1. 4. The plasma reactor according to claim 1, wherein the thickness of the frit 6 varies over the entire length and width within the reactor. 5 The thickness of the frit 6 varies within the cross section of the reactor, in other words, it increases from one edge toward the center and decreases toward the other edge across the entire width of the reactor. A plasma reactor according to claim 4.