Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2000-08-16
2001-06-05
Coe, Philip R. (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S022180, C134S023000, C134S032000, C134S152000, C134S16600C, C134S16700R
Reexamination Certificate
active
06240934
ABSTRACT:
SPECIFICATION
The invention relates to a method and to a device for treating very small holes or recesses extending into workpieces with liquid treatment media.
Should workpiece surfaces be treated with liquids, the surfaces are as a rule brought into contact with the treatment media by immersion. Typical examples of usage are represented by the cleaning of substrates, for example of covering pieces, the electroplating treatment of metal parts and plastic material parts and also the electro-plating procedures in the production of circuit boards.
In many areas of technology thin metal layers are applied to the surfaces of materials, in order to impart to the surfaces certain properties, which are required for the use of materials in cases of industrial application. Although there is already a multitude of varying coating techniques available, electro-plating metal plating methods still represent important treatment methods despite the frequent occurence of problems specific to the procedure.
For example, problems can arise, when workpieces with very small holes or with other recesses, which extend into the surface of the workpieces and have small dimensions, are to be treated with liquid medium. In this case these holes and recesses are not adequately or not at all washed through, with the result that the desired treatment cannot be achieved.
In circuit board technology for example the sides of the holes, which extend through the circuit board laminate or which are inserted as blind bores, are provided with a metal layer. For this purpose, after being produced, for example by drilling, these holes or recesses have firstly to be cleared of impurities generally, for example of resin smears caused by boring on the drilled hole wall while the circuit board is brought into contact with etching agents. Furthermore, chemical solutions with surface-active substances (wetting agents) are inserted also for cleaning the holes. After cleaning, the electrically insulating drilled hole walls are activated with solutions containing a noble metal and subsequently are copper-plated or nickel-plated, as a rule with electroless metallization solutions. Then a metal layer with a thickness of roughly 20 &mgr;m is deposited by means of electrolytic plating on the wall surfaces of the holes.
Because of the miniaturisation of circuit structures on circuit boards, smaller and smaller holes are being formed, for example with a diameter of 0.2 mm, in circuit boards, which still need to be reliably plated. For this reason there exist various methods for removing air from these holes and ensuring an adequate exchange of liquid between the inside of the hole and the liquid treatment medium outwith the holes. Special methods are employed for flushing out these very small holes.
In the German Patent document DE 35 28 575 A1 there is known, for this purpose, a method for cleaning, activating and/or plating boreholes in horizontally placed circuit boards, in which the circuit boards run over a drenching line at a constant speed, said line being formed by a jet arranged beneath the travelling line and perpendicular to the direction of movement, and in which the liquid treatment medium is conveyed in the form of a vertical wave to the underside of the circuit board and also a device for carrying out this method is known.
Further papers have been published on this method describing special applications for flushing out drilled holes in circuit boards (for example in DE 36 38 630 A1, DE 36 24 481 A1).
Another solution can be drawn from the German Patent document DE 39 05 100 C2, in which a method is given for the chemical and electrolytic surface treatment of board-shaped workpieces, which are furnished with small openings, in aqueous solutions, the workpiece having two autonomous vibration movements which are independent of one another. The first of the two vibration movements extends perpendicular to the surface of the workpiece and the second in roughly the same direction as the first and at the same time as the latter, the frequency of the first movement being essentially lower than the frequency of the second, representing a heavily pulsating oscillation in quick sucession. The amplitude of the first vibrating movement is essentially greater than the amplitude of the second.
Numerical simulations for determining the flow conditions in drilled holes of circuit boards have shown in addition that oscillations of that type, orientated perpendicular to the surface of the circuit boards, assist the liquid exchange more effectively than oscillations which have vibration components exclusively parallel to the circuit board surface.
However the mentioned solutions to the problem of reliably treating very small holes and especially blind bores are not suitable, since, in these cases, the flow only works in the entry region of the holes. Blind bores and other recesses extend only to a definite depth in a workpiece or solid body. Apart from problems arising also from very small clearance holes, the problem exists here as well in that the liquid flowing in must also flow out again to attain an adequate liquid exchange. Otherwise, at best a very slow material exchange would be possible by means of diffusion.
Because of the boundary layer adhering to the hole wall or because of a finite viscosity from applicable treatment liquids, a through-flow by means of vibration movements cannot be produced in these holes at a depth, which for example, when using aqueous treatment liquids, corresponds approximately to the diameter of the hole.
In order to treat circuit boards with blind bores it is normal for example to treat the circuit boards in a device, in which the circuit boards are introduced in a horizontal position and horizontal direction through a treatment chamber; the circuit boards being situated within the treatment liquid during passage. In this way, it can at least be achieved, that gas bubbles which are situated in the holes on the top of the circuit boards can be removed relatively simply. A reliable exchange of material within the time available for treatment and particularly the removal of the gas bubbles from the holes on the underside of the circuit boards is however not possible with this method. Moreover even gas bubbles can no longer be removed with certainty, using this method, from holes in which the ratio of hole length to hole diameter exceeds a value of approximately 1.
Hence the problem underlying the invention is to avoid the disadvantages of the state of the art and particularly to find a reliable method and a device suited to the purpose of flushing holes provided in workpieces and other tiny hollow spaces, opening outwards, and also recesses with an opening width below 0.5 mm with a liquid treatment medium. In particular, a method and device for treating circuit boards provided with blind bores is to be produced.
The solution to the problem consists in directing a liquid jet of the treatment medium on to the surface of the substrate to be treated which has a diameter which is smaller than the opening width of the holes or recesses, i.e. in drilled holes of the diameter of the holes to be treated in the surface of the substrate. By substrate is meant any solid body or workpiece to be treated. By means of this it is possible to direct a flow of treatment medium into the inside of the holes and recesses such that an effective rinsing of the blind bore is also achieved even when these holes have a very small diameter, for example of 75 &mgr;m. The jet directed into the inside of the recess is reversed at its base, so that, within the hole, jets of treatment medium which are directed outwards are also formed.
According to the invention, this is effective primarily when the jet of treatment medium has a diameter, which at most amounts to half the diameter of the hole. If a jet has a diameter which is greater than the diameter of the hole, then the flow effect, according to the invention, can no longer be achieved in the hole.
REFERENCES:
patent: 4119439 (1978-10-01), Boucher
patent: 4559664 (1985-12-01),
Brenn Gunter
Durst Franz
Meyer Heinrich
Schafer Michael
Streup Heribert
Atotech Deutschland GmbH
Coe Philip R.
Paul & Paul
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