TWM657323U - Equipment used to detect defects inside the ABF layer - Google Patents

Abstract

The utility model relates to a device for detecting internal faults of an ABF layer. The technical solution of the utility model provides a solution for testing open circuit and short circuit faults hidden in the ABF layer, and it can help manufacturers isolate faults on traces in the ABF layer before mounting the die on the ABF layer, which cannot be accomplished by the AOI method.

Description

Equipment for detecting internal faults in ABF layers

This novel invention relates to a device for detecting internal faults in ABF layers.

ABF (Ajinomoto stacked film) can be used for laser drilling and fine trace/space processing and has been widely used in substrates for modern packages such as BGA (ball grid array). However, with the increase in the number of layers and the reduction in the size and pitch of copper or other metal traces, existing solutions (such as AOI (automatic optical inspection)) cannot conveniently test faults inside the ABF layer.

In addition, existing VTEP (vectorless test extended performance) boards are too large, so the capacitive coupling is not localized enough to a single trace under test in the ABF layer, so an open or short fault on the trace may be masked. Moreover, due to the extremely small size of the ABF layer trace, the capacitive coupling is small and it is difficult to detect the received signal for pure capacitance measurement.

Therefore, a method and apparatus for testing open and short circuit faults hidden in the ABF substrate is needed.

This practical and novel technical solution provides a solution for testing open and short circuit faults in the ABF layer, and it can help manufacturers isolate faults on traces in the ABF layer before mounting the die on the ABF layer, which is impossible to accomplish with the AOI method.

This practical new technical solution has the following advantages:

1. It can test open circuit and short circuit faults hidden in the ABF layer, which AOI cannot do.

2. The technology is cost-effective compared to X-ray methods. This can be achieved by relying on our mature frequency response measurement products.

3. Series inductance can be introduced with excitation to help convert pure capacitance measurement into a more sensitive frequency response measurement in a relatively low frequency band. In conjunction with more localized capacitive coupling, the solution presented in this utility model can help overcome the shortcomings due to the VTEP board approach. Without connecting the series inductance, a wider frequency band may be required to monitor the inherent resonant characteristics of the ABF trace for fault detection, and the equivalent inductance of the resonance comes from the structure of the trace.

Specifically, the utility model relates to a device for detecting internal faults of an ABF layer, the device comprising: a contact probe that contacts a metal material at the bottom of the ABF layer to establish an electrical contact point; a non-contact probe that is located at the top of the ABF layer and points to the point where the contact probe trace comes out of the ABF layer, so that localized capacitive coupling will be established between the non-contact probe and the point where the trace comes out of the ABF layer; an external connection with two or more excitation ports; and, optionally, one or more inductors that are connected in series with the contact probe to achieve LC resonance between the excitation ports.

Preferably, the apparatus includes means for measuring S11, S21 or Z11 (for detecting open circuit or short circuit faults).

In one embodiment, the device of the utility model includes two excitation ports used separately, wherein the first excitation port, the series inductor and the localized capacitive coupling together form a test loop, and an LC resonance will be formed in the loop. Preferably, the device also includes: a device for measuring S11, S22, Z11 or Z22 (for detecting open circuit faults), and/or a device for measuring Z33 or the resistance between two traces inside the ABF layer (for detecting short circuit faults) and a third excitation port.

When using the device of the utility model, if the curve showing the value or phase of S11, S21, S22, Z11 or Z22 shifts to the right, it can be determined that the ABF layer to be tested has an open circuit fault; if the curve of S21 or Z33 does not show significant changes over the entire frequency span, it can be determined that the ABF layer to be tested has a short circuit fault.

It is understood by those skilled in the art that the technical solution of the utility model inherently also relates to a method for detecting internal faults of an ABF layer, which is characterized in that it includes the following steps: arranging a contact probe, the contact probe contacts the metal material at the bottom of the ABF layer to establish an electrical contact point; arranging a non-contact probe, the non-contact probe is located at the top of the ABF layer and points to the contact probe. The point where the trace emerges from the ABF layer, so that localized capacitive coupling will be established between the non-contact probe and the point where the trace emerges from the ABF layer; arranging an external connection with two or more excitation ports; and, optionally, arranging one or more inductors, the one or more inductors being connected in series with the contact probe to achieve LC resonance between the excitation ports.

Preferably, the method includes measuring S11, Z11 or S21 (for detecting open circuit or short circuit faults).

In one embodiment, the method includes arranging two excitation ports for separate use, wherein the first excitation port, the series inductor and the localized capacitive coupling together form a test loop, and an LC resonance is formed in the loop; and the method preferably includes: measuring S11, S22, Z11 or Z22 (for detecting open circuit faults), and/or arranging a third excitation port and measuring Z33 or the resistance between two traces inside the ABF layer (for detecting short circuit faults).

In the method, if the curve showing the magnitude or phase of S11, S21, S22, Z11 or Z22 shifts to the right, it can be determined that the ABF layer to be tested has an open circuit fault; if the curve of S21 or Z33 does not show a significant change over the entire frequency span, it can be determined that the ABF layer to be tested has a short circuit fault.

L1, L2: Inductor

10: Substrate

20: Solder ball

Figure 1 shows an overview of the first sensing setup of the utility model, where (1) shows a contact probe on the bottom of the ABF layer, (2) shows the trace to be measured inside the ABF layer, (3) shows the localized capacitive couplings C1 and C2, (4) shows the protective layer on top of the ABF, and (5) shows a non-contact probe on top of the ABF layer (which can contact the protective layer but not the ABF).

Figure 2 shows an overview of the second sensing setup of the utility model, where (1) shows the contact probe on the bottom of the ABF layer, (2) shows the trace to be tested inside the ABF layer, (3) shows the localized capacitive couplings C1 and C2, (4) shows the protective layer on top of the ABF, (5) shows the non-contact probe on top of the ABF layer (which can contact the protective layer but not the ABF) and (6) shows the external connections.

FIG3 shows typical faults generated on the trace inside the ABF layer of the present utility model, where (1) shows an open circuit fault and (2) shows a short circuit fault.

FIG4 shows an equivalent circuit for explaining the detection principle of the first sensing setting, wherein (a) shows a reference; (b) shows an open circuit fault on trace 1, and a dotted circle represents an open circuit fault; and (c) shows a short circuit fault between two traces, and a dotted circle represents a short circuit fault.

Figure 5 shows the simulation results of the first sensing setup, detecting open and short faults based on the S21 amplitude, where curve 1 represents the reference S21, curve 2 represents the open fault S21 on trace 1, curve 3 represents the open fault S21 on trace 2, and curve 4 represents the short fault S21.

Figure 6 shows the simulation results of the first sensing setup, detecting open and short faults based on the S21 phase, where curve 1 represents the reference S21 phase, curve 2 represents the S21 phase for a short fault, curve 3 represents the S21 phase for an open fault on trace 1, and curve 4 represents the S21 phase for an open fault on trace 2.

Figure 7 shows the simulation results of the first sensing setup, detecting open and short faults based on the Z11 phase, where curve 1 represents the reference Z11 phase, curve 2 represents the Z11 phase for an open fault on trace 1, curve 3 represents the Z11 phase for an open fault on trace 2, and curve 4 represents the Z11 phase for a short fault.

Figure 8 shows the simulation results of the second sensing setup by checking S11 and S22 for open circuit fault detection, where curve 1 represents the benchmark of S11 without open circuit fault, curve 2 represents the benchmark of S22, curve 3 represents S22 with open circuit fault, and curve 4 represents S11 with open circuit fault.

Figure 9 shows the simulation results of the second sensing setup by checking the Z11 and Z22 phases for open circuit fault detection, where curve 1 represents the Z11 reference phase, curve 2 represents the Z22 reference phase, curve 3 represents the phase with Z22 having an open circuit fault, and curve 4 represents the phase with Z11 having an open circuit fault.

Figure 10 shows the simulation results of the second sensing setup, short-circuit fault detection by checking the Z33 amplitude (it is also possible to check the resistance using only DC measurement), where curve 1 represents Z33 for a short-circuit fault condition, and curve 2 represents Z33 for a baseline without a short-circuit fault.

The term "fault" in this context includes both open circuit faults and short circuit faults.

The parameters S11 (input reflection coefficient or return loss of the first port), S21 (transmission coefficient between two interleaved loops), S22 (output reflection coefficient or return loss of the second port), Z11 (open circuit impedance of port 1), Z22 (open circuit impedance of port 2) and Z33 (open circuit impedance of port 3) all have meanings known in the art. The measurement of the parameters (including the generation of curves) can also be carried out in a conventional manner by means within the device or by means of external means under conventional conditions known to those skilled in the art.

The implementation scheme of the utility model is shown in Figures 1 to 3. Figure 1 shows a first test setup for detecting internal faults of the ABF layer of the substrate 10, where a contact probe is used to contact the metal material (e.g., solder ball 20) at the bottom of the ABF layer to establish an electrical contact point, while a non-contact probe is on the top of the ABF layer, and the probe is pointing to the point where the contact probe trace comes out of the ABF layer, so that localized capacitive coupling will be established between the non-contact probe and the point where the trace comes out of the ABF layer. In addition, one or more inductors are used to be connected in series with the contact probe to achieve LC resonance between two excitation ports in the test setup. In addition, FIG. 3 shows a typical fault simulated in this disclosure, where two open faults tested are generated on traces inside the ABF layer, and a short fault is generated between two traces.

The detection principle of this (first) sensing setup can be explained using the simplified equivalent circuit shown in Figure 4. When an open circuit fault occurs on any trace inside the ABF layer, it will destroy the original trace (modeled as an additional capacitor C3 in Figure 4), and thus the resonant frequency of the transmission between the two ports will increase, as shown in the simulation results in Figure 5-7.

When a short circuit fault occurs, the transmission between the two ports will be short-circuited due to the short circuit fault. Therefore, as shown in FIG5 , when a short circuit fault occurs between the two traces to be tested, the transmission between the two ports will be almost close to 0.

In addition, defects can also be detected by measuring S11 or Z11, as shown in Figure 7, based on the same principle explained in the above paragraph.

Another sensing setup (second one) is shown in Figure 2. For open fault detection, either excitation port 1 or port 2 can be used alone. For port 1, it forms a test loop with localized capacitive coupling C1 together with the series inductor L1, and LC resonance will be formed inside the loop. Therefore, any open fault occurring in the loop (on the trace inside the ABF layer) will change the resonant characteristics by reducing the equivalent capacitance and be detected by the frequency response measurement of the S11 or Z11 parameters, as shown in Figures 8 to 10. For short fault detection, excitation port 3 can be used to check the Z33 amplitude (or just check the resistance between the two traces inside the ABF layer, because a short fault will cause a significant reduction in resistance).

Compared to the first sensing solution that tests pairs of traces, the second sensing solution can test a single trace at a time. Therefore, in order to cover more possible sensing solutions, this disclosure provides a supplementary solution.

Implementation example: Simulation results of fault detection

Numerical simulations were performed to verify the fault detection capability of the present invention, setting the inductance L1 and L2 to 500nH, and it can be a single inductor or several inductors in series. For the case where no inductor is used, the inductance from the ABF trace will shift the resonant frequency to a relatively high value.

Figures 5 and 6 show the simulation results of the first sensing setup. When an open circuit fault occurs on the internal trace of the ABF layer, the S21 curve (along with the maximum transmission frequency) will shift to the right, and this is caused by the reduction of the equivalent capacitance of the LC resonance. If we choose to measure the power transfer at a certain frequency (for example, at 1.05GHz), the open circuit fault will cause the power transfer to decrease by about 30dB, or 1000 times. When a short circuit fault occurs, the power transfer will be significantly reduced to a constant (almost 0) over the entire frequency span, and it can be explained by the equivalent circuit shown in Figure 4.

Figure 6 shows another alternative using the phase of S21 as an indicator for detecting faults. For an open circuit fault, the resonant frequency (phase equal to 0 frequency point) will shift to the right, while for a short circuit fault, the phase remains constant over the entire frequency span.

Figure 7 shows another alternative to using the measurement results of S11 or Z11 as an indicator for detecting faults. Similar to the results of Figure 6, when an open circuit fault exists, the resonant frequency will shift to the right; while for a short circuit fault, the change in phase over the entire frequency span is negligible.

Figures 8 to 10 show the simulation results of the second sensing setup. As shown in Figures 8 and 9, similar to the first sensing setup, an open-circuit fault will cause the equivalent capacitance to decrease, thus shifting the resonant frequency to the right. For the short-circuit fault detection result using the excitation port 3 as shown in Figure 10, it will reduce the Z33 impedance magnitude or the resistance between the two traces to almost a constant over the entire frequency span, so the short-circuit fault can be easily detected.

The simulation results shown above demonstrate that this practical new technology solution can solve the challenge of detecting open or short faults hidden in the ABF layer used in modern packages, which cannot be accomplished by traditional AOI methods. The simulation results shown in this disclosure document verify how to detect faults by frequency response measurements using the above parameters, or by monitoring the transmitted power at a single frequency point. Considering the increased density and shrinking size of ABF layers used in modern IC packages, the solution proposed in this article will become more important for future IC package test solutions to isolate open and short faults in ABF substrates at an early stage.

L1, L2: Inductor

10: Substrate

20: Solder ball

Claims (5)

An apparatus for detecting internal faults of an ABF layer, the apparatus comprising: a contact probe that contacts the metal material at the bottom of the ABF layer to establish an electrical contact point; a non-contact probe that is located on the top of the ABF layer and points to the point where the contact probe trace exits the ABF layer, so that localized capacitive coupling will be established between the non-contact probe and the point where the trace exits the ABF layer; an external connection having two or more excitation ports; and, optionally, one or more inductors that are connected in series with the contact probe to achieve LC resonance between the excitation ports. An apparatus for detecting internal faults of an ABF layer as described in claim 1, comprising a device for measuring S11, S21 or Z11. An apparatus for detecting internal faults of an ABF layer as described in claim 1 comprises two excitation ports used separately, wherein the first excitation port, the series inductor and the localized capacitive coupling together form a test loop, and an LC resonance is formed in the loop. An apparatus for detecting internal faults of an ABF layer as described in claim 3, comprising a device for measuring S11, S22, Z11 or Z22. An apparatus for detecting internal faults of an ABF layer as described in claim 3, comprising a device for measuring Z33 or the resistance between two traces inside the ABF layer and a third excitation port.