Evaluating copper plating in a pth

Abstract

A device comprising a connector configured to electrically connect a measurement device on an annular ring on a first side of a Plated Through Hole (PTH), a probe connected to the measurement device and configured to touch an interior wall of the PTH at a first location, a motor control and a motor to move the probe in the PTH, and a sensor, in the measurement device, to detect electrical measurements through the PTH from the connector to the probe.

Description

EVALUATING COPPER PLATING IN A PTHBACKGROUND

[0001] Plated Through Hole (PTH) technology is a mainstay in Printed Circuit Board (PCB) technology. It supports robust electrical and mechanical connections, making it indispensable in industries like aerospace, automotive, and industrial equipment. While Surface Mount Technology (SMT) dominates due to its ability to support higher component densities and automated assembly, PTH is still essential for components that require secure mounting and for multi-layer interconnections. Current advancements in PTH technology focus on improving manufacturing precision and material quality to enhance performance and durability.SUMMARY

[0002] Aspects of the present invention relate to a device comprising a connector configured to electrically connect a measurement device on an annular ring on a first side of a PTH, a probe connected to the measurement device and configured to touch an interior wall of the PTH at a first location, a motor control and a motor to move the probe in the PTH, and a sensor, in the measurement device, to detect electrical measurements through the PTH from the connector to the probe.

[0003] Further aspects of the present invention relate to a method forming a connection with a connector with an annular ring on first side of a PTH, inserting a probe into the PTH from the second side of the PTH, making contact between the probe an interior wall of the PTH, and taking a measurement of electrical properties of the PTH between the connector and the probe.

[0004] Further aspects of the present invention relate to a method comprising drilling a hole in a PCB, depositing copper in the hole to form a PTH with an annular ring on a first side of the PTH, forming a connection between a measurement device and the annular ring, inserting a probe, connected to the measurement device, into a second side of the PTH, touching the probe to a point on an interior surface of the PTH, and taking a reading of electrical properties of the PTH between the probe and the annular.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The drawings included in the present application are incorporated into and form part of the specification. They illustrate embodiments of the present invention and, along with the description, serve toexplain the principles of the invention. The drawings are only illustrative of certain embodiments and do not limit the invention.

[0006] FIG. 1 illustrates an example schematic of closed loop when copper is present in the Plated Through Hole (PTH).

[0007] FIG. 2 illustrates an example schematic of open loop when copper is absent in the PTH.

[0008] FIG. 3 illustrates a cross sectional slice view of an exemplary PTH in a PCB with example testing components, according to various embodiments of the present invention.

[0009] FIG. 4 illustrates a cross sectional slice view of an exemplary PTH in a PCB with example testing components, according to various embodiments of the present invention.

[0010] FIG. 5 illustrates a cross sectional slice view of an exemplary PTH in a PCB with example testing components, according to various embodiments of the present invention.

[0011] FIG. 6 illustrates a cross sectional slice view of an exemplary PTH in a PCB with example testing components, according to various embodiments of the present invention.

[0012] FIG. 7 illustrates an example method for investigating copper plating in a PTH, according to various embodiments of the present invention.DETAILED DESCRIPTION

[0013] Aspects of the present invention relate to evaluating copper plating in a Plated Through Hole (PTH). While the present invention is not necessarily limited to such applications, various aspects of the invention may be appreciated through a discussion of various examples using this context.

[0014] In the current generation of Printed Circuit Boards (PCB) products, the aspect ratios continue to become larger, and the accuracy of backdrill depth becomes more vital.

[0015] Many main planar boards and IO cards had or were suspected of having thin or missing plating defects in backdri lied holes and were found to have longer back drill stubs. Current backdrill stub tolerance 9 ± 5 mils.

[0016] These defects could possibly cause fails in the field that were not caught in manufacturing / build tests due to the test methods not being robust enough. In some instances, defects may include SI (System Integration) defects or electrical opens. In some instances, SI defects, or electrical opens, refer to issues in electronic circuits where a break or discontinuity in the conductive path occurs. This interruption prevents electrical signals from properly traveling through the circuit.

[0017] New quality assurance methods must be developed to decrease the probability of defective backdrilled PTHs escaping quality checks. Common PTH Failures points include cracking due to thermal stress, opens developed during the manufacturing process, oxidation, and longer back drill stub detriments affecting signal integrity at higher speeds.

[0018] PCB suppliers continually have issues with thin plating in backdrilled plated through holes and out of spec backdrill stubs. Millions of dollars of product has been recalled and caused disruption to delivering systems to customers on time. The defects that made it into systems required additional internal resources to monitor system performance through its life.

[0019] The current methods of non-linear compensation (NLC), time-domain reflectometry (TDR) and 4- wire testing are not always robust enough to catch plating defects of this type, and eddy current tests to characterize backdrill striping does not measure stub length.

[0020] Many PCB specifications require a minimum of 1 mil of plating thickness in a PTH in order to be robust enough to survive 88,000 hours of field use thermal cycling which ranges from 25°C to 85°C.

[0021] In some instances, in a backdrilled PTH, there is potential for missing plating based on the resist opening size used. If a ‘size on size' or negative resist opening is used, there is potential for missing plating defects of various levels of severity.

[0022] In some embodiments, a testing device that uses a probe to detect copper along the PTH wall to test for electrical continuity is proposed. In some embodiments, the proposed test differs from other electrical tests for testing backdrilled holes (4-wire testing) as it can detect missing plating in parts of the PTH by physically probing various location. In some embodiments, as the proposed method is an electrical test, there is less propensity to miss defects of lesser severity. FIG. 1 and 2 show examples of circuit 100 when copper is / not present with the proposed test. In some embodiments, the example circuit 100 may include a measurement tool 150 and a region 125 representing the PTH. FIG 1. depicts a schematic of closed loop when copper is present in the PTH. FIG 2. Depicts a schematic of an open loop when copper is absent in the PTH. In some embodiments, the measuring device can be an Analong or a Digital Multimeter (AMM / DMM) capable of measuring resistance.

[0023] Fig. 3 depicts a cross sectional slice view of exemplary PTH 300 in PCB 350 with example testing components. In some embodiments, only the section of PCB 350 with PTH 300 is depicted. PCB 350 may have many PTH and other components (not depicted) outside of the small section depicted in FIG 3. In some embodiments, copper has been plated on PTH 300 forming annular ring 305 on a first side of the PCB / PTHand copper plating 310 on the walls of the PTH. In FIG. 3, the copper has not been deposited uniformly, depicted by the left side of plating 310 not extending as far as the right side of plating 310 where copper plating was intended to be deposited uniformly through the PTH 300. In some embodiments, a connector 315 may be placed on annular ring 305. In some embodiments, connector 315 is a conductive material made to interface with a metal contact such as annular ring 305. In some embodiments, connector 315 may be connected to measurement tool 360. In some embodiments, PCB 350 may include one or more layers of conductive material 340 and dielectric 345 or other materials (not depicted) used in multilayer PCBs. In some embodiments, a probe 320, connected to measurement tool 360, may be inserted into the PTH 300 and placed against the surface of the PTH 300 making contact with the PTH 300. In some embodiments, the probe may be directed along a path such as path 322. In some embodiments, the probe may be used by measurement tool 360 to take and record several measurements along the interior surface of PTH as the probe travels along the path 322 to one or more locations. In some embodiments, the measurements may be from electrical currents and / or voltage, applied by measurement tool 360, running from the annular ring to the copper plating 310. Possible paths will be discussed further below. In some embodiments, the device includes connector 315, measurement tool 360, probe 320, a motor (not depicted), and a motor controller (not depicted). One skilled in the art will understand that the device may take on multiple configurations and need other components to implement the device. In some embodiments, measurement tool 360 may have one or more sensors configured to detect electrical measurements such as a current, voltage, voltage drop, or resistance from connector 315 to probe 320.

[0024] In some embodiments, the resistive probe approach described herein identifies PTHs walls with missing copper due to improper etching line parameters in the manufacturing line, improper backdrill (striping), and / or exposed copper planes that may be caused by improper backdrilling. In some embodiments, the resistive probes may characterize copper in PTHs vias walls by characterizing the electrical continuity in the copper wall. In some embodiments, voids in copper may appear as an open, while copper in PTHs be characterized as a closed loop of current with the magnitude of the current indicating the quality of the copper plating.

[0025] In some embodiments, Ohms law may be used to characterize the existence of copper in the PTH wall given the high conductivity of copper.

[0026] In some embodiments, the disclosed test may be automated and use a flying probe approach.

[0027] Fig. 4 depicts a cross sectional slice view of an exemplary PTH 400 in PCB 450. In some embodiments, only the section of PCB 450 with the PTH 400 is depicted. PCB 450 may have many PTH and other components (not depicted) outside of the small section depicted in FIG 4. In some embodiments,copper has been plated on PTH 400 forming annular ring 405 and copper plating 410 on the walls of the PTH 400. In FIG. 4, the copper has non-uniform plating, depicted by the steps in plating 410 where copper plating was intended to be deposited uniformly through PTH 400. For example, dotted lines 412 depict the intended deposition of copper. In some embodiments, a connection point 415 may be placed on annular ring 405. In some embodiments, connection point 415 may be connected to measurement tool 460. In some embodiments, PCB 450 may include one or more layers of conductive material 440 and dielectric 445 or other materials (not depicted) used in multilayer PCBs. In some embodiments, a probe 420, connected to measurement tool 460, may be inserted into PTH 400 and placed against the surface of the PTH 400. In some embodiments, the probe may be directed along a path such as path 422. In some embodiments, the probe may take several measurements along the interior surface of the PTH 400 as it travels along the path 422. In some embodiments, the area 492 is thinner than the intended thickness depicted in area 490. Thus, as probe 420 passes over area 494 the current reading, read by measurement tool 460, changes indicating a decreased in the comprehensiveness of the copper plating. In some embodiments, when probe 420 is over area 494, measurement tool may read an open circuit, indicating that there is no copper plating present.

[0028] Fig. 5 depicts a cross sectional view of an exemplary PTH 500 in PCB 550. In the previous views, only thin slice of a PCB was shown, in Fig. 5 the cross sectional view also depicts the section of PCB 550 behind the cross sectional plane (e.g., the visible back wall of PTH 500). In some embodiments, only the section of PCB 550 with the PTH 500 is depicted. PCB 550 may have many PTH and other components (not depicted) outside of the small section depicted in FIG 5. In some embodiments, copper has been plated on the PTH 500 forming annular ring 505 and copper plating 510 on the walls of the PTH 500. In FIG. 5, the copper has not been deposited uniformly, depicted by the steps in plating 510 where copper plating was intended to be deposited uniformly through the PTH 500. For example, In FIG. 5, the PTH 500 was intended to have a uniform coating completely covering the conductive material at point 595. In some embodiments, a connection point 515 may be placed on annular ring 505. In some embodiments, connection point 515 may be connected to measurement tool 560. In some embodiments, PCB 550 may include one or more layers of conductive material 540 and dielectric 545 or other materials (not depicted) used in multilayer PCBs. In some embodiments, a probe 520, connected to measurement tool 560, may be inserted into the PTH 500 and placed against the surface of the PTH 500. In some embodiments, the probe may be directed along a path such as path 522. In some embodiments, the probe may take several measurements along the interior surface of the PTH 500 as it travels along the path 522. In some embodiments, the PTH 500 has been backdril led, see area 501 . In some embodiments, probe 520 may detect the depth of the backdri Hi ng . For example, in FIG 5 if backdrilling was intended to leave a complete connection between conductive material 541 and copper plating 510, however as depicted the backdrilling removed material from the interface from at point 595. In some embodiments, the probe may detect that no copper is present bellow point 595 and thus the backdrilling may have removed more material than intended. For example, since more material wasremoved than was intended the interface between copper plating and the conductive material 541 may be compromised.

[0029] Fig. 6 depicts a top down view of PCB 650 with a PTH 600. In some embodiments, path 622 depicts a path that a probe 620 may follow. In some embodiments, path 622 may be used in combination with paths (e.g., path 322, 422, and 522) going into and out of the PTH 600. For example, probe 620 may corkscrew around the walls of PTH 600 going deeper with each revolution. For example, the probe 620 may complete a complete a first circle around the wall of the PTH 600 at a first dept and then move deeper incrementally completing subsequent circles around the walls of the PTH 600. For example, the probe 620 may move deeper into the PTH 600 and then withdraw to the edge of the PTH 600 before rotating incrementally around the wall of the PTH 600 and repeating the process. In some embodiments, as the advances along the path it may stop incrementally to take measurements, or the system may take measurements as the probe 620 is moving. As will be understood by one skilled in the art, the path that the probe 620 follows may be designed to investigate a particular failure point or feature consideration. In some embodiments, a location of the probe 620 is based on velocity and time measurements recorded during movement of the probe 620.

[0030] FIG. 7 depicts an example method 700 for investigating copper plating in a PTH.

[0031] Method 700 begins with operation 705 of forming a PTH in a PCB. In some embodiments, the PTH may be formed in a hole in the multilayer PCB. In some embodiments, copper plating is intended to be uniformly deposited in the hole. In some instances, a PTH may be created by drilling and plating a hole through the PCB to create connections between layers. The PTH may have an annular ring (e.g., a capture pad) at one end or both ends). In some embodiments, after the necessary connections are established, a secondary drilling process, known as backdrilling may be performed. In some instances, backdrilling removes the unused portion of the hole, called the stub, which extends beyond the last connected layer. This removal reduces signal reflections and interference caused by the stub, resulting in cleaner signal transmission and improved performance of high-speed circuits.

[0032] In some instances, forming a PTH is a manufacturing process used to ensure reliable electrical connections between layers of a PCB. In some instances, a hole is drilled through a PCB in a location that requires interlayer connectivity. In some instances, a cleaning process may be used to remove any debris or contaminants. In some embodiments, an electroless plating process deposits a thin layer of copper on the walls of the holes and on the surface to form an annular ring. In some instances, the electroless plating is followed by electroplating, which adds more copper to increase the thickness and conductivity of the platedPTH. In some instances, a protective solder mask may be applied, and surface finishes such as gold or tin may be added to protect the copper and prepare it for component soldering.

[0033] Method 700 continues with operation 710 of making an electrical connection with the annular ring on the first side of the PTH.

[0034] Method 700 continues with operation 715 of inserting a probe on the second (e.g., opposite the annular ring) side of the PTH. In some embodiments, the probe may be inserted such that it touches an interior wall of the PTH. In some embodiments, the probe may be inserted to a set distance inside of the PTH and at a particular placement of the PTH. For example, the PTH may have a designated placement system such as degrees of rotation (e.g., 0 may be the starting point, 180 may be the opposite side PTH from the starting point, and 360 may bring the probe back to the starting point). For example, the depth may be set at 1 mil, 5 mils, or 10 mils (where a mill is a thousandth of an inch). The particular size and feathers of the PTH may dictate a different coordinate system without deviation from the system disclosed herein.

[0035] Method 700 continues with operation 720 of taking an electrical measurement. In some embodiments, the electrical measurement may be a resistance measurement between the annular ring and the probe. For example, if there is a very high resistance or no conductivity there may be a lapse in the copper plating of the PTH. In some embodiments, the electrical measurement may be a current measurement between the annular ring and the probe. For example, the current measurement may be used to indicate the presence of copper plating at the probe or between the probe and the annular ring. In some embodiments, a resistive threshold may be defined such that any resistance (e.g, an infinite or a resistance above 2x10-8Q-m) above the threshold indicates a break or effective break in the plating between the probe and the annular ring.

[0036] Method 700 continues with operation 725 of stepping the probe to a new position of the PTH. As described herein, the stepping of the probe may be designed to generate a picture of the metal coating inside the PTH (the metal coating is described as copper herein but may be any suitable material). In some embodiments, the stepping may bring the probe to a new position inside the PTH. In some embodiments, velocity of probing (change in x) / (change in y) may be used to identify depth location of measurement of interest. In some embodiments, the initial time measurement (at the point of entry) may act as a point of reference, all subsequent measurement may give a time signature that may be used to know depth of measurement using equation 1 and 2 or other similar equations.

[0037] sec =ts- tp* (Equation 1).

[0038] V = ^7 * sec = mils (Equation 2).

[0039] In some embodiments, ts— Time Signature and tp— Probe Start Time.

[0040] Method 700 continues with operation 730 of analyzing the measurements to determining if the PTH has been explored completely by the probe or the probe is at the end of the PTH. If the probe is at the end of the PTH, the method may continue to operation 730. If the probe has not finished exploring the PTH, the system may return to operation 715.

[0041] Method 700 continues with operation 735 of characterizing the depth and / or location of any measured anomalies (e.g., anomalous readings) by the distance / time measurements from operation 720. In some embodiments, there may be expected / acceptable measurement parameter indicating an acceptable thickness and / or coverage of copper in the PTH. In some embodiments, if the electrical measurements are within a tolerance, there is no need to calculate a resistive value of the copper plating. In some embodiments, a deviation from the expected measurements may indicate an issue with the plating and thus an evaluation of the plating at those points may be performed, based on the measurements, as described herein. For example, if no voltage and / or current is detected at the probe it may indicate there is an absence of plating. The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustration, and combinations of blocks in the block diagrams and / or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

[0042] The descriptions of the various embodiments of the present invention have been presented for purposes of illustration but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope of the described embodiments. The terminology used herein was chosen to explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

[0043] In a preferred embodiment of the present invention described herein, there is provided a method comprising: drilling a hole in a PCB; depositing copper in the hole to form a Plated Through Hole (PTH) with an annular ring on a first side of the PTH; forming a connection between a measurement device and the annular ring; inserting a probe, connected to the measurement device, into a second side of the PTH; touching the probe to a point on an interior surface of the PTH; and taking a reading of electrical properties of the PTH between the probe and the annular ring. The method may further comprise: recording a position of the measurement based on the velocity, direction, and travel time of the probe. The method may further comprise: determining if the measurement is outside of an acceptable reading; and recording the position as an anomalous reading. The method may further comprise calculating, based on a determination that the measurement is outside of an acceptable reading, a resistive value, wherein the calculating is based on a current reading at the probe with a known voltage being applied at the annular ring. The method may further comprise: determining, based on a resistance measurement above a threshold, that there is an absence of the coating at the position of the anomalous reading. The method may further comprise: moving the probe to a new position along the interior wall of the PTH; and measuring the electrical properties of the PTH between the connector and the probe at the new position.

Claims

CLAIMS1. A device comprising: a connector configured to electrically connect a measurement device on an annular ring on a first side of a Plated Through Hole (PTH); a probe connected to the measurement device and configured to touch an interior wall of the PTH at a first location; a motor control and a motor to move the probe in the PTH; and a sensor, in the measurement device, to detect electrical measurements through the PTH from the connector to the probe.

2. The device of claim 1, wherein the measurement device is configured to detect a voltage drop through the PTH from the annular ring to the probe.

3. The device of claim 1, wherein the measurement device is configured to detect a current running from the annular ring to the probe given an applied voltage.

4. The device of claim 1, wherein the motor is configured to incrementally step the probe along an interior surface of the PTH.

5. The device of claim 1, wherein the first location of the probe is based on velocity and time measurements recorded during movement of the probe.

6. The device of claim 1, wherein an anomalous reading at a position indicates an absence of a coating at the position.

7. A method comprising: forming a connection with a connector with an annular ring on a first side of a Plated Through Hole (PTH); inserting a probe into the PTH from a second end of the PTH; making contact between the probe an interior wall of the PTH; and taking a measurement of electrical properties of the PTH between the connector and the probe.

8. The method of claim 7, further comprising: recording a position of the measurement based on the velocity, direction, and travel time of the probe.

9. The method of claim 8 further comprising:determining if the measurement is outside of an acceptable measurement parameter; and recording the position as an anomalous reading.

10. The method of claim 9; calculating, based on a determination that the measurement is outside of the acceptable measurement parameter, a resistive value, wherein the calculating is based on a current reading at the probe with a known voltage being applied at the annular ring.11 . The method of claim 9 further comprising: determining, based on a resistance measurement above a threshold, that there is an absence of a coating at a position of the anomalous reading.

12. The method of claim 7 further comprising: moving the probe to a new position along the interior wall of the PTH; and measuring the electrical properties of the PTH between the connector and the probe at the new position.

13. The method of claim 7 further comprising: repeating the moving and measuring at to record measurements at set points along the PTH.

14. The method of claim 7 further comprising: applying a voltage to the annular ring through the connector.

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