JPH0749363A - Short circuit detection for chip-on-board substrate - Google Patents

Abstract

PURPOSE:To provide a short circuit detection method for a chip-on-board substrate by which a short circuit is surely detected with a simple structure and method. CONSTITUTION:Between two signal lines, where presence of short circuit is inspected, the signal of the same level is made to flow (S1). and power supply current IV1 at that time is measured (S2). Then the signal of different level is made to flow (S3) between them, and power supply current IV2 then is measured (S4). Then, IV2-IV1 is obtained (S5), and if it is above a specified threshold alpha, it is decided that short circuit has occurred (S6).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip-on-board (COB) in which a plurality of semiconductor elements such as integrated circuits are mounted on a printed wiring board, and the elements are connected by electrical connecting means such as wire bonding. The present invention relates to a method for detecting a short circuit on a substrate.

[0002]

2. Description of the Related Art FIG. 5 shows a COB mounted with a semiconductor element.
1 is a printed wiring board, 2 is a printed wiring pattern formed on the printed wiring board 1, 3, 4
Is an IC mounted on this printed wiring board 1.
The terminals 3 and 4 and the printed wiring pattern 2 are electrically connected by a bonding wire 5 as a signal input / output line.

Further, in order to electrically connect the IC 3 and the IC 4 as well, the terminals of the ICs 3 and 4 are directly connected by the bonding wire 5 without the interposition of the printed wiring board 1. FIG. 6 is an explanatory view showing another example of a COB substrate on which a semiconductor element is mounted, 6 is a printed wiring board, 7 is a printed wiring pattern formed on this printed wiring board 6, and 8 is this printed wiring board. An IC mounted on 6 and an IC mounted on this IC 8 are electrically connected by a bonding wire 10 as a signal input / output line between the terminal of the IC 8 and the printed wiring pattern 7. .

In order to mount the IC 9 on the IC 8 for electrical connection, the terminals of the ICs 8 and 9 are mounted by solder balls 11 to electrically and mechanically connect the both. FIG. 7 is an equivalent circuit showing the connection between the ICs 3 and 4 and between the ICs 8 and 9 shown in FIG. In general, when connecting ICs to each other, the input terminal of one IC is connected to the output terminal of the other IC, and the output terminal of one IC is connected to the input terminal of the other IC.

In the figure, 12 is an output buffer of the ICs 3 and 8, 13 is an input buffer of the ICs 4 and 9, and the output buffer 12 and the input buffer 13 are electrically connected by a signal line 14. As the signal line, as shown in FIG. 5, the terminals of the IC are connected by bonding wires, or as shown in FIG.
There is a type in which the terminals of the IC are connected with solder balls.

Similarly, 15 is an input buffer of the ICs 3 and 8, 16 is an output buffer of the ICs 4 and 9, and the input buffer 15 and the output buffer 16 are electrically connected by a signal line 17. An input / output switchable input / output line called a tristate may be used as a signal line connecting the ICs.

After mounting the IC on the printed wiring board as described above, a test program is executed in order to confirm the operation. This test program repeats input and output of test data, which is a combination of a predetermined input signal and output signal, in every predetermined cycle called a test cycle, and whether it operates as expected. A test is performed to see if it is correct.

According to this test, the COB substrate which has become defective due to a cause such as a defect at the time of manufacture, an open, a short circuit or a circuit breakage is rejected.

[0009]

However, in the case of directly connecting ICs, in the above-described conventional method for inspecting a chip-on-board substrate, a signal is transmitted when the connection between ICs is open. It will not be done, so
While 100% detection is possible by switching the input to all terminals to Low level and High level, there is a problem that this may not be possible for short detection.

That is, FIG. 8 is an explanatory view showing a conventional problem, of the two output buffers 21 and 22, the High level is input to the output buffer 21, and the output buffer 2
When the output of these output buffers 21 and 22 is shorted when the Low level is input to 2, the signal value becomes H
It takes an intermediate value between the high level and the low level. At this time, due to variations in the thresholds of the two input buffers 25 and 26 connected to the output buffers 21 and 22 and the signal lines 23 and 24, the input buffer 25 has an intermediate level between the high level and the low level. High level is output from the value signal, and the input buffer 26
Then, the Low level may be output from a signal having an intermediate value between the High level and the Low level, and as a result, it may be the same as the normal case. In this way, even if there is a short circuit, a correct result may happen accidentally with respect to the input test data, and in this case, there is a problem that the short circuit cannot be detected.

Further, FIG. 9 is an explanatory view showing another conventional problem, which is provided with a selector 29 for selecting the output of the two input buffers 27, 28.
When the circuit configuration is such that the outputs of 28 cannot be detected at the same time, there are variations in the capabilities of the two output buffers 32 and 33 connected to the input buffers 27 and 28 via the signal lines 30 and 31, respectively. For example, when the output buffer 32 has a low capacity and the output buffer 33 has a high capacity, a high level is input to the output buffer 32 and a low level is input to the output buffer 33. At this time, the output buffer 32 and the output buffer 33 are input. When the output of is short-circuited, the value of the signal becomes close to the low level.

Here, if the thresholds of the input buffers 27 and 28 are equal, the outputs of both the input buffers 27 and 28 are at the low level. At this time, the selector 29
Therefore, when the output of the input buffer 28 is selected to be taken out, the output from the selector 29 is at the low level, but the input of the output buffer 33 is at the low level, so the signal lines 30 and 31 are short-circuited. Even if there is not, the output of the input buffer 28 is at the Low level, and depending on the state of the selector 29, the result may be the same as the normal case. In this way, even if there is a short circuit, a correct result may happen accidentally with respect to the input test data, and in this case, there is a problem that the short circuit cannot be detected.

Therefore, in the case of short-circuit detection, it is necessary to increase the test data and test a large number of combination patterns to increase the detection rate in order to prevent defective products from being shipped. There is a problem that the test time becomes long and the test efficiency decreases. FIG. 10 is an explanatory view showing an example of a conventional countermeasure for surely detecting a short circuit. In order to monitor a signal on a signal line 36 connecting between two ICs 34 and 35, wiring patterns 37 for taking out test terminals are individually provided. Signal line 3
Although the signal lines 36 are provided corresponding to No. 6 and the signal line 36 is connected through the wiring pattern 37, the wiring density 37 for the test causes a problem that the mounting density is reduced.

FIG. 11 is an equivalent circuit showing another example of conventional countermeasures, in which 38 is an output buffer of one IC and 39 is an output buffer.
Is an input buffer of the other IC, 40 is a signal line connecting between them, and the test terminal 41 is connected to the input side IC itself.
Is provided and connected to the analog switch 42 so that a signal can be taken out from any test terminal 41.
A halfway level at the time of short circuit can be detected, but a special circuit needs to be provided on the integrated circuit, which causes a problem that the IC becomes expensive.

The present invention has been made in order to solve the problem that a short circuit at a connection point between ICs on a chip-on-board substrate cannot be reliably detected.
It is an object of the present invention to provide a short-circuit detection method for a chip-on-board substrate, which can detect a short circuit reliably by using a short test program without modifying an IC or a printed wiring board on which the IC is mounted.

[0016]

In order to achieve this object, the present invention comprises a plurality of semiconductor elements mounted on a printed wiring board, and the semiconductor elements are electrically connected by a plurality of signal lines. In the short-circuit detection method for a chip-on-board substrate, a means for detecting and measuring the power supply current of the chip-on-board substrate is provided, and a signal of the same level and a different level are provided between the two signal lines that are to be inspected for the presence of a short circuit. Signal is applied, the power supply current in each case is measured, and the difference between the power supply current when a signal of the same level and the power supply current when a signal of a different level is applied is detected between the two signal lines. It is characterized by detecting a short circuit.

[0017]

According to the present invention described above, first, a signal of the same level is made to flow between two signal lines whose presence or absence of a short circuit is to be inspected, and the power supply current in that case is measured. Next, signals of different levels are passed between the two signal lines, and the power supply current in that case is measured. Then, if the difference between the power supply current when a signal of a different level is passed and the power supply current when a signal of the same level is passed is large, a short circuit has occurred.
This can be removed as a defective product.

[0018]

Embodiments Embodiments will be described below with reference to the drawings.
FIG. 1 is a flowchart showing a short-circuit detecting method for a chip-on-board substrate according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a configuration for executing the short-circuit detecting method for a chip-on-board according to the present embodiment. The configuration of this embodiment will be described with reference to FIG.

In the figure, numeral 51 indicates a plurality of I on the printed wiring board.
This is a chip-on-board (COB) substrate on which C or the like is mounted, and the structure of this COB substrate 51 is the same as that described in FIG. 5 or FIG. 6 described above. Reference numeral 52 denotes a COB prober which is detachably connectable to a terminal or the like of the COB substrate 51 capable of measuring the power supply current, and 53.
Is a logic tester such as a general-purpose IC tester which is connected to the COB prober 52 and which inputs and outputs only the logic level to measure the logic level. These configurations have been conventionally used for the inspection of the COB substrate. It is used.

Reference numeral 54 is a power supply current detection circuit connected to the COB prober 52 and capable of detecting a current and measuring the change thereof. The power supply current detection circuit 54 is composed of an A / D converter or the like, and is provided on the COB substrate 51. It is possible to receive the power supply current flowing in the IC of the above through the COB prober 52, detect this, and measure the change. In addition, in some large-scale general-purpose testers, in addition to the logic level measurement, the power-supply current can be detected and measured by the tester itself. In this case, the general-purpose tester can be used for the logic tester 53 and the power-supply current detection circuit 54. Can be used instead of.

FIG. 3 is an equivalent circuit of a connecting portion between ICs on the COB substrate 51. Reference numerals 55 and 56 are ICs, 57 is a plurality of output buffers constituting one IC 55, and 58 is a plurality constituting another IC 56. Is a signal line for connecting the output of each output buffer 57 and the input of each input buffer 58, and is +5 to each output buffer 57.
Power such as V is supplied. As the signal line 59, the terminals of the IC are connected by bonding wires as shown in FIG. 5, or as shown in FIG.
There is a type in which the terminals of the IC are connected with solder balls.

Here, for example, the signal line 59a and the signal line 59
When b is short-circuited, these signal lines 59a, 59
If the levels of the signals input to the output buffers 57a and 57b that output signals to b are different, the output buffer 5
An abnormally large current flows between 7a and 57b, which is reflected in the power supply current. In this embodiment, a short circuit is detected by utilizing this change in power supply current.

FIG. 4 is an explanatory diagram showing an example of the test data used in the present embodiment. The test data is such that signals of the same level flow between the two signal lines 59 to be inspected for the presence or absence of a short circuit. And the combinations 1 and 2 for inputting signals of the same level to the respective output buffers 57, and the respective output buffers 57 so that signals of different levels flow between the two signal lines 59 whose presence or absence of the short circuit is to be inspected. It consists of combinations 3 and 4 for inputting a level signal.

That is, in the combination 1 or 2, in order to pass the signal of the same level between the two signal lines 59 to be inspected for the presence or absence of the short circuit, for example, in the combination 1, the low level signal is input to the output buffer 57a. In this case, the output buffer 57a outputs a signal to the signal line 59b which may be short-circuited with the output of the output buffer 57a.
A low-level signal is also input to b, and there is a possibility that the output of the output buffer 57b may be short-circuited with the signal line 59c.
A low-level signal is also input to the output buffer 57c that allows a signal to flow to the.

In the combination 2, contrary to the combination 1, the high level signal is input to the output buffer 57a, so that the high level signal is also input to the output buffer 57b and the output buffer 57c. ing. Further, in the combination 3 or 4, in order to allow signals of different levels to flow between the two signal lines 59 to be inspected for the presence or absence of short circuit, in the combination 3, the output buffer 57 is used.
If a high-level signal is input to a, the output buffer 57b that outputs a signal to the signal line 59b that may short-circuit the output of the output buffer 57a is L
A high-level signal is input to the output buffer 57c which inputs a low-level signal and causes a signal to flow through the signal line 59c which may short-circuit the output of the output buffer 57b.

Further, in the combination 4, contrary to the combination 3, the low level signal is input to the output buffer 57a, the high level signal is input to the output buffer 57b, and the low level signal is input to the output buffer 57c. It is designed to input a level signal. Then, a test program is created so that these can be input to each output buffer 57 at a predetermined timing, and the test program executes the COB substrate short-circuit detection method of this embodiment.

The test data is not limited to the combination shown in FIG. 4, and both the signal of the same level and the signal of a different level can be input between the two signal lines whose presence or absence of the short circuit is to be inspected. Good. The processing procedure of the COB substrate short circuit detection method in this embodiment will be described below with reference to FIG.

In this embodiment, the test data described with reference to FIG. 4 is used. The test data of the combination 1 and the combination 2 described in FIG. 4 is input to each output buffer 57 so that signals of the same level flow between the two signal lines 59 that are to be inspected for a short circuit (S
1) At this time, the power supply current flowing through the ICs 55 and 56 is detected by the power supply current detection circuit 54 and measured (S).
2).

Next, it is desired to inspect for the presence or absence of the short circuit 2
The combination 3 described in FIG. 4 is applied to each output buffer 57 so that signals of different levels flow between the signal lines 59 of the book.
And the test data of the combination 4 is input (S3), the power supply current flowing through the ICs 55 and 56 at this time is detected by the power supply current detection circuit 54, and this is measured (S4). here,
The measured value of the power supply current when the signals of the same level are input to the respective output buffers 57 is IV1 measured so that the signals of the same level flow between the two signal lines 59 to be inspected for the presence or absence of a short circuit, measured in S2. The measured value of the power supply current when the signals of different levels are input to the output buffers 57 so that the signals of different levels flow between the two signal lines 59 which are to be inspected for the presence or absence of the short circuit, measured in S4. IV
If it is 2, the difference (IV2-IV1) between the measured value of the power supply current when the signals of different levels are input and the measured value of the power supply current when the signals of the same level are input is obtained and this (IV2 -IV1) is determined whether it is larger than a preset threshold α (S5).

The threshold α is the amount of change in the power supply current due to the operation of the IC logic, and is set according to the difference in the impedance of the IC. Above S
In (5), if (IV1−IV2) ≧ α, it is determined that one of the signal lines is short-circuited and a short-circuit current is flowing, and this is rejected (S6). Also, in S5 above,
If (IV1−IV2) <α, it is determined that there is no short circuit (S7).

In the short-circuit detection method of this embodiment, if any one short-circuit can be detected, it is possible to inspect the presence / absence of a short-circuit at all connection points between ICs at a time, and the amount of test data is small. Test data by many combinations as in the past is unnecessary. As described above, in the method of detecting a short circuit on the COB substrate of the present embodiment, the short circuit is detected from the change in the power supply current. Even with a push-pull type buffer in which the signal level is a halfway value and it is difficult to detect a short circuit, the short circuit can be detected reliably.

[0032]

As described above, according to the present invention, a signal of the same level and a signal of a different level are made to flow between two signal lines whose presence or absence is to be inspected, and the power supply current in each case is measured. Since the short circuit between the two signal lines is detected from the difference between the power supply current when the signals of different levels are supplied and the power supply current when the signals of the same level are supplied, the mounting density is reduced. Changing the wiring of the chip-on-board board or making the IC expensive
There is an effect that a short circuit can be surely detected without changing the circuit configuration.

Since the short circuit is detected from the change in the power supply current when the same signal flows and when different signals flow as described above, the data amount of the test program improves at least the short circuit detection rate and the test time. Since it can be shortened, the test efficiency can be improved. Therefore, the manufacturing cost of the chip-on-board substrate can be reduced by improving the test efficiency, and the quality can be improved by improving the short-circuit detection rate.

[Brief description of drawings]

FIG. 1 is a flowchart showing a flow of a short-circuit detection method in an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the configuration of the present embodiment.

FIG. 3 is an equivalent circuit of a connecting portion between ICs on a COB substrate.

FIG. 4 is an explanatory diagram showing an example of test data of the present embodiment.

FIG. 5 is an explanatory diagram showing an example of a COB substrate.

FIG. 6 is an explanatory diagram showing another COB substrate.

FIG. 7 is an equivalent circuit of a connecting portion between ICs on a COB substrate.

FIG. 8 is an explanatory diagram showing a conventional problem.

FIG. 9 is an explanatory diagram showing other conventional problems.

FIG. 10 is an explanatory diagram showing a conventional countermeasure example.

FIG. 11 is an equivalent circuit showing another conventional countermeasure example.

[Explanation of symbols]

 51 COB board 54 Power supply current detection circuit

Claims (1)

[Claims] 1. A short-circuit detection method for a chip-on-board substrate, comprising: mounting a plurality of semiconductor devices on a printed wiring board; and electrically connecting the semiconductor devices by a plurality of signal lines. A means for detecting the power supply current and measuring it is provided, and a signal of the same level and a signal of a different level are sent between the two signal lines that are to be inspected for the presence of a short circuit, and the power supply current in each case is measured. , A short circuit between the two signal lines is detected from the difference between the power supply current when a signal of a different level is supplied and the power supply current when a signal of the same level is supplied. Short detection method.