Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-06-24
2001-02-13
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S211000, C204S229800, C204S230200
Reexamination Certificate
active
06187153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improvements in plating processes and equipment, and more particularly to improvements in methods and apparatuses for monitoring performance of plating apparatuses, particularly for use in plating palladium onto integrated circuit leadframes.
2. Relevant Background
Leadframes are electrically conducting structures that are used in the manufacture of packaged integrated circuit devices. Typically, a semiconductor chip is mounted onto or adjacent a leadframe, which includes a number of leads or conductors by which connections can be made to other circuitry, and the circuits of the chip are selectively connected to the leads. After the chip and leads are connected, a portion of the leadframe and the chip are encapsulated to form a package, usually of plastic, in which the chip is delivered and used.
In the construction of many leadframes, the leadframe may be coated with palladium to provide desired conductivity and other properties, and to facilitate the bonding of gold connection wires between the leadframe and the chip. The layer of palladium is a usually of importance to customers because the palladium plays an important part in enabling proper bonding of the gold wires that connect the chip to the leadframe and of enabling solid connections to be made to the leads of the leadframe in use.
However, in order to provide the desired palladium coating, multiple underlying coats are generally required. For example, on a copper leadframe, usually four conductive coats are successively electroplated onto the leadframe structure to assure the integrity of the top palladium layer. To assure that the palladium “sticks” and has the proper electrical characteristics, typically, the layer immediately below the palladium layer is nickel.
In most manufacturing processes, which are usually under computer control, however, failures in the computer system may go undetected for some time. This may result in production of potentially large lots of unacceptable leadframes. It may be, in fact, possible for defective product to be shipped to the customer, resulting in the subsequent production of parts which may not meet specifications and which may require expensive identification, correction, and substitution of proper parts.
To address these problems, frequently the production lines have been monitored by x-ray equipment, in which the thickness of the material being deposited is x-rayed. Such x-ray monitoring, however, requires manual operation, and also requires expensive equipment, which itself requires expensive regulation and maintenance.
What is needed, therefore, is a method and apparatus for monitoring the electroplating process so that if the conditions required for proper palladium electroplating become improper to form the desired palladium layer, an operator can be warned, or, optionally, the production line can be automatically shut down.
SUMMARY OF THE INVENTION
In light of the above, therefore, it is an object of the invention to provide a method and apparatus for monitoring the electroplating process which warns the operator, or, optionally, automatically shuts down the production line if the conditions required for proper palladium electroplating become improper to form the desired palladium layer.
It is another object of the invention to provide a method and apparatus of the type described, which can be used in conjunction with an electroplating line that is operated under computer control, and which operates independently of the computer and its control.
It is yet another object of the invention to provide a method and apparatus for monitoring the electroplating currents in an electroplating machine, wherein if a current in a palladium depositing cell falls below a current in a nickel depositing cell, a signal is generated, which may be used to stop the electroplating machine.
These and other objects, features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of the invention, when read in conjunction with the accompanying drawings and appended claims.
The method and circuit of the invention uses electronic circuitry, which may be redundant to the a computer plating operating and monitoring system used in conjunction with a leadframe electroplating production line. The circuitry monitors a plating function in the process which has a known amperage to provide a reference current that can be compared to the amperage required in the palladium cell. For example, the reference cell may be a nickel strike head, which generally requires less current than the palladium cell, when operating on leadframes having the same surface area. The circuit compares the amperage in the palladium cell to the reference cell. If the amperage in the palladium head falls below the amperage of the nickel strike head, the line can be automatically shut down, or an alarm can be generated to warn the operator of a potentially failing condition.
Thus, according to a broad aspect of the invention, a method is presented for monitoring the operation of an electroplating machine of the type which has least two cells for depositing at least two different metals sequentially onto a substrate, which may be an integrated circuit leadframe, or the like. The method includes comparing a first electroplating current in a first one of the cells with a second electroplating current in a second one of the cells. If the electroplating machine is operating normally, the first current is less than the second current. If however, the second current is less than the first current, an error signal is generated. If desired, the method may also include stopping the electroplating machine in response to the error signal.
The method may also include conditioning the first and second signals prior to the comparing step to reduce effects of any common mode differences or ground loops. The step of comparing a first electroplating current in the first cell with a second electroplating current in the second cell comprises comparing a first electroplating current in a cell in which nickel is deposited with a second electroplating current in a cell in which palladium is deposited.
According to another broad aspect of the invention, a method for monitoring an electroplating operation of an electroplating machine is presented. The electroplating machine is of the type which has a first electroplating cell for depositing nickel onto an integrated circuit leadframe and a second electroplating cell for subsequently depositing palladium onto the leadframe. The method includes applying a first current to the first electroplating cell to form a nickel deposit on a leadframe substrate and applying a second current to the second electroplating cell to from a palladium deposit on the nickel deposit. The second current is greater than the first current if the electroplating machine in operating normally. The first current and second currents are compared during the electroplating operation, and if the second current is less than the first current, an error signal is generated. If desired, the electroplating machine may be stopped in response to the error signal.
According to yet another broad aspect of the invention, an electroplating machine is presented. The electroplating machine has a first cell for depositing a first metal onto a substrate, and a second cell for depositing a second metal onto the substrate. A first current generator applies a first current to the first cell during a first electroplating process, and a second current generator applies a second current to the second cell during a second electroplating process. The second current is larger than the first current during normal operation of the electroplating machine. A comparator is connected to compare a magnitude of the first current with a magnitude of the second current, to produce an output when the second current is less than the first current. Optionally, a circuit is provided for stopping the electroplating machine in response to
Drew David M.
Moehle Paul R.
Brady III W. James
Garner Jacqueline J.
Gorgos Kathryn
Leader William T.
Telecky , Jr. Frederick J.
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