JP3053323B2 - High speed plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed plating method using a pulse current.

[0002]

2. Description of the Related Art Nickel,
Electroplating of gold, silver, palladium and the like is performed. FIG. 7 (B) shows a method of plating the surface of the lead frame 80. A plating solution jet 82 from a nozzle 81 is shown.
Was generated, and the jet 82 was sprayed on the surface of the lead frame 80, and the surface of the lead frame 80 was plated by applying a current using a DC power supply (not shown) (hereinafter, this method is referred to as a jet plating method). .

[0003]

However, in the above-mentioned jet plating method, the plating solution does not
Flows from the central part to the peripheral part, and when plating is performed with continuous energization, the plating solution has a high concentration in the central part. On the other hand, since the plating solution from which the plating metal has already been removed to some extent flows in the peripheral portion, the plating solution concentration decreases, and as a result, the plating thickness in the central portion increases, as shown in FIG. This causes a phenomenon that the peripheral portion becomes thin. Therefore, as shown in FIG. 6, when the jet plating method by pulse current providing an off-time during the power-on period is performed, the strong plating solution blown out from the nozzle 81 flows to the peripheral portion during the non-power-on period, and the plating solution having a high concentration is discharged. Since power is supplied while covering the surface of the lead frame 80, the plating thickness can be theoretically made uniform. However, in the pulse plating method, in order to obtain a uniform plating thickness, the off time (T _Off ) is theoretically set to be equal to or longer than the time when the plating solution passes through the surface of the lead frame 80, and the on time (T _Off ) is set. _ON ) must be within a short range where the concentration of the plating solution does not unbalancely decrease, and the overall plating amount is proportional to the current value according to Faraday's law. There was a problem of falling. Therefore, in the actual plating line, the pulse plating method is adopted, but the off-time (T _Off ) is appropriately shortened, and plating is performed with a strong current to improve productivity. Therefore, the plating thickness at the center (mainly the pad portion) of the lead frame is thick and the plating thickness at the tip of the lead is thin. In this case, plating is performed based on the plating thickness at the tip of the lead. There was a problem that it was uneconomical. In addition, such a problem occurs not only in the jet plating method but also in a plating method in which a plating solution flows. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a high-speed plating method capable of making the plating thickness more uniform.

[0004]

According to the present invention, there is provided a semiconductor device comprising:
The high-speed plating method described is a high-speed plating method using a flowing plating solution and applying a positive pulse to a planar plating target to perform plating. A negative pulse smaller than the positive pulse is applied to perform more uniform plating on the surface of the plating object.

[0005]

In the high-speed plating method according to the first aspect of the present invention, a negative pulse whose average value is smaller than the positive pulse is supplied during the rest period in the pulse plating method. During this period, the plating metal formed on the surface of the plating object becomes ions again and moves downstream. In this case, the metal that has turned into ions (ie, electropolished) from the protruding plating metal portion flows downstream along with the flow of the plating solution, and thus, a period during which a negative pulse current flows, that is, Even when the time during which the positive pulse current serving as the plating current is interrupted is short, the concentration of the plating solution on the downstream side is ensured, so that a more uniform plating thickness can be obtained. Since the total plating amount is proportional to the current supplied according to Faraday's law, the average value of the positive pulse current needs to be sufficiently larger than the average value of the negative pulse current.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will now be described with reference to the accompanying drawings to provide an understanding of the present invention. 1 is a graph showing a waveform of a plating current according to one embodiment of the present invention, FIG. 2 is a graph showing a waveform of a plating current according to another embodiment, and FIG. 3 is a schematic block diagram of a power supply device for high-speed plating. FIG. 4 is a circuit diagram of a power supply unit and a power control unit. FIG. 5 is an external view of a power supply device for high-speed plating.

First, a power supply unit for high-speed plating will be described. As shown in FIG. 3, a DC power supply of two circuits connected in series in a power supply unit 11 is formed from a commercial power supply of 200 V AC. The DC power supply is controlled to generate positive and negative pulses. FIG. 4 shows the details of the power supply unit 11 and the power control unit 12. The power supply unit 11 includes a transformer 1 connected to 200 VAC.
3 and a rectifier 1 connected to the secondary side of the transformer 13
4 and 15 and constitutes two power supplies connected in series. The power control unit 12 performs waveform shaping by the power MOS FETs 16 and 17 connected to the two power supplies, and can output a pulse current of a predetermined current or voltage.

In the stage preceding the power MOS FETs 16 and 17, transistors 19 and 20 for driving the power MOS FETs 16 and 17 by dividing the pulse signal input by the operational amplifier 18 into a plus signal and a minus signal. Is provided. And the power control unit 1
2 is a shunt 2 for detecting plating current on the output side.
1 is provided so that the plating current and the plating voltage can be fed back.

As shown in FIG. 3, the power control unit 12
The arithmetic and control unit 22 for controlling C
The central processing unit 23 includes a PU, a ROM in which a program is described, and a RAM for temporarily storing operation data. The central information processing unit 23
4, a communication control unit 25 for receiving a signal of the RS-422 or RS-232C standard, and an analog input unit 27 which has an AD converter therein and converts an input analog signal into a digital signal and inputs the digital signal; LED display section 28 for displaying current and voltage, liquid crystal display section 29 for displaying a measured current waveform and a preset waveform, I / O control section 30 for performing input and output to the outside, and data of past plating conditions Alternatively, a waveform data memory unit 31 for storing newly set plating condition data and the like is connected.

The current and voltage data measured from the output side of the power control unit 12 are input to a measurement unit 32 having an AD converter therein, and are converted into digital signals.
The signal processing is performed by the central information processing unit 23, and even if there is disturbance such as a change in the concentration of the plating solution, the waveform of the output current or the output voltage is controlled to be constant within a set range, and the current value and the current value are controlled. The voltage value is displayed on an LED display unit 28 provided separately as shown in FIG. The output of the waveform data memory unit 31 is processed by an analog control unit 33, converted into an analog pulse signal having a constant positive and negative height and width, and input to the operational amplifier 18.

The plating solution is stored in a plating tank (not shown), is pumped up by a pump, and is blown out from a nozzle. The plating tank has a thermometer for measuring the plating solution temperature and a concentration meter for measuring the concentration of the plating solution. These outputs are transmitted to the central information processing section 23 via an analog input section 27. Then, as shown in the central information processing section 23 as an example in Japanese Patent Application Laid-Open No. 5-263299 filed earlier by the present applicant, the temperature and concentration of the plating solution, the pulse period, the positive pulse energizing time,
With the positive pulse current value, the negative pulse conduction time, and the state value of the negative pulse current value as inputs, perform a fuzzy inference on the plating state, compare the inferred value with a set value determined by previously required plating conditions, There is provided a fuzzy control program for inferring an optimum control value of the state value by repeating fuzzy feedback for adding and subtracting a correction value to and from the inference value until the inference value determined by the fuzzy inference matches the set value.

That is, under appropriate conditions, an appropriate pulse current including a negative pulse is applied as shown in FIG.
When plating is performed by a method as shown in the following, when the plating solution is energized when the plating solution covers the back surface of the lead frame 80 which is an example of a planar plating object, plating is performed with a plating solution having a uniform concentration. When a positive pulse is applied, plating is performed to a uniform thickness. However, if the cycle of the positive pulse current is short, a plurality of platings will be performed while the plating solution passes through the lead frame surface, and the plating solution in the peripheral portion becomes thinner and the plating thickness becomes thinner. When a negative pulse current is applied during the positive pulse rest period, the plating metal attached near the center of the lead frame is electrolyzed and metal ions move to the periphery, so that the plating solution can be made uniform, thereby Uniform plating can be performed.
In this case, the pulse conditions are different depending on the plating state value when the plating solution pump pressure is constant.Therefore, fuzzy inference is performed for various conditions, the current waveform is determined, and the plating speed is also determined. The optimum control value is inferred in consideration of the above.

These conditions are input from the key input unit 24 and are displayed on the LCD display unit 29. In addition, while monitoring the actual plating state, the waveforms of the plating current and the plating voltage are measured, converted into digital signals by the measuring unit 32, converted into signals by the central information processing unit 23,
This is displayed on the D display unit 29. FIG. 5 shows an LCD display unit 29.
Is shown, the plating conditions can be set and monitored while observing the current waveform (voltage waveform in some cases). The preset optimal control value is stored in the waveform data memory unit, and when plating is performed, the optimal waveform that meets the conditions is selected by the central information processing unit 23, and this is actually selected by the analog control unit 33. , And applied to the power control unit 12.

FIGS. 2A to 2C show current waveforms including a negative pulse current according to another embodiment, but the waveforms can be selectively set according to plating conditions. It is to be noted that other current waveforms can be selected and set, and can be freely used by being stored in the waveform data memory unit.

[0015]

According to the high-speed plating method of the present invention, since a negative pulse current can be passed in addition to a positive pulse current for plating, a flowing plating solution is used. When plating is performed, the plating solution in a portion where the plating solution becomes thin can be covered by passing a negative pulse current, and thereby more uniform plating can be performed. In addition, it is possible to increase the negative pulse current value and reduce the pulse width, so that the plating time can be reduced by 20 to 30% as compared with the normal pulse current plating. For this reason, the productivity of plating can be significantly increased.

[Brief description of the drawings]

FIG. 1 is a graph showing a waveform of a plating current according to one embodiment of the present invention.

FIG. 2 is a graph showing a waveform of a plating current according to another example.

FIG. 3 is a schematic block diagram of a power supply device for high-speed plating.

FIG. 4 is a circuit diagram of a power supply unit and a power control unit.

FIG. 5 is an external view of a power supply device for high-speed plating.

FIG. 6 is a current waveform of pulse plating according to a conventional example.

FIG. 7 is an explanatory diagram of a plating state.

[Explanation of symbols]

11: power supply unit, 12: power control unit, 13: transformer,
14: Rectifier, 15: Rectifier, 16: Power MOS · F
ET, 17: power MOS-FET, 18: operational amplifier, 19: transistor, 20: transistor, 21:
Shunt, 22: arithmetic control unit, 23: central information processing unit,
24: key input unit, 25: communication control unit, 27: analog input unit, 28: LED display unit, 29: LCD display unit, 3
0: I / O control unit, 31: waveform data memory unit, 32:
Measuring unit 33: Analog control unit

Claims (1)

(57) [Claims] In a high-speed plating method in which a positive pulse is applied to a planar plating object by using a flowing plating solution to perform plating, an average value of the positive pulse is measured during all pauses of the positive pulse. A high-speed plating method, characterized in that a negative pulse smaller than the above pulse is energized to perform more uniform plating on the surface of the object to be plated.