WO2013113766A1

WO2013113766A1 - A method of discovering a risk for damaged components in electronic assemblies

Info

Publication number: WO2013113766A1
Application number: PCT/EP2013/051820
Authority: WO
Inventors: Nils Jacobsson; Roger Jonasson
Original assignee: Micronic Mydata AB
Priority date: 2012-01-31
Filing date: 2013-01-30
Publication date: 2013-08-08

Abstract

The invention relates to a method of discovering a risk for damaged components in electronic assemblies. The method includes: at a component pick and place mounting device, monitoring a mounting of a component on a workpiece, such as a circuit board, by means of at least one electro-static discharge sensor arranged at the device; and detecting electro-static discharge events during said mounting of the component. Further, the invention relates to a component mounting device for pick and place mounting, including a component mounting head configured to pick and place mount components on a circuit board; and at least one electro-static discharge sensor configured to detect electro-static discharge events during mounting of the components.

Description

A METHOD OF DISCOVERING A RISK FOR DAMAGED

COMPONENTS IN ELECTRONIC ASSEMBLIES BACKGROUND [0001] The technology disclosed relates to protection of device mounting processes from potentially device -killing electro-static discharge (ESD) events. In particular, it relates to discovering a risk for damaged components in electronic assemblies caused by ESD events during component mounting.

[0002] ESD has been recognized as a problem during chip manufacturing. Some patent publications have addressed problems during device manufacturing, for reticles and wafer transport. One of the tooling components of chip making is reticles, also known as masks. US Patent 6,614,235, col. 2, discloses tagging reticles with ESD sensor tags to detect ESD events that might justify re-inspection of a reticle, prior to continued use. The reference emphasizes the high cost of individual reticles and the value of protecting them with individual tags.

[0003] Combination of an ESD sensor with a wafer transport container is described in Pat. Pub. No. US 2010/0051692 Al . Results of sensing ESD events experienced by a wafer carrier could be monitored either via RFID or Zigbee RF connection, according to the reference.

[0004] An ESD sensor design is described in US Patent 5,796,256. In addition, 3M™ markets an EM Eye Meter for ESD event measurement. However, in addition to the drawbacks mentioned above, there is no prior art solution for handling ESD events in a process of mounting components on a substrate. SUMMARY [0005] It is an object of the present invention to provide a method of discovering a risk for damaged components in electronic assemblies caused by ESD events during component mounting.

[0006] The object is achieved by a method of discovering a risk for damaged components in electronic assemblies, according to the present invention as defined in claim 1, and by a pick and place mounting device and system according to the present invention as defined in claims 13 and 16. [0007] Thus, according to an aspect of the invention, there is provided a method of discovering a risk for damaged components in electronic assemblies, including: at a component pick and place mounting device, monitoring a mounting of a component on a workpiece by means of at least one electro -static discharge sensor arranged at the device; and further by detecting electro-static discharge events during said mounting of the component. [0008] By detecting electro-static discharge (ESD) events during the very mounting of components, and by doing this by means of monitoring the mounting process, it is possible discover a risk for damaged components, and to do that without having to equip every component with an ESD sensor. The latter is often practically impossible due to the small dimensions of the components.

[0009] For the purposes of this application, it should be noted that the expression "pick and place mounting" is understood by the person skilled in the art as describing the very mounting operation where a component mounting head is moved to a component feeder area, where the mounting head picks one or more components from one or more of the component feeders, and then is moved to a mounting area where the mounting head places the component or components on the workpiece such as a circuit board. Furthermore, the expression "circuit board" is to be broadly interpreted as any kind of substrate that is provided with components.

[0010] For the purpose of this application, a "workpiece" may be a circuit board, a substrate, a thin film or similar. The workpiece may be stationary or be moving during the placement of the components on the workpiece and the concurrent detection of electro-static discharge events. The workpiece in form of a substrate or film may e.g. be mounted on or supported by a stationary or movable support table, or may e.g. be supported by a

continuously moving stage or a stage that is both configured to move a workpiece, e.g. a web- shaped workpiece, stepwise forward and provide for the concurrent placement of the components on the workpiece and detection of electro-static discharge events.

[0011] In one implementation of the method, occurrences of the ESD events are recorded. Thereby, subsequent analyzes can be performed.

[0012] In one implementation, the method comprises recording, for each ESD event, properties of the ESD event. The recording of properties include recording a strength of the electro-static discharge event; and recording at least one of an identification of the component presently being mounted and a position of the mounting head at the occurrence of the electro- static discharge event. These properties are useful for further analyzing. By either identifying the component or identifying the position of the mounting head, or both, subsequent fault detection is facilitated.

[0013] In one implementation, the method comprises analyzing the properties of at least one of the electro-static discharge events; and determining, on basis of said analysis, whether or not the corresponding workpiece is at risk of failure. This is a general subsequent analysis, which in turn can be used for more detailed analyses, and which reduces the burden of more detailed analyses by providing information about which workpieces are not at risk of failure.

[0014] In one implementation, the method comprises subjecting a workpiece determined to be at risk of failure to stress testing.

[0015] In one implementation, the method includes testing a component determined to be subject to an electro-static discharge, and further approving the component as tested and incorporating the component into a finished assembly.

[0016] In one implementation, the method includes testing a component determined to be subject to an electro-static discharge, and further requiring rework of, or replacing, the component tested and incorporating the reworked component, or the replacement component, into a finished assembly.

[0017] In one implementation, the method includes monitoring a component during pick and place assembly, and further approving the component as not having been subjected to electro-static discharge during assembly and incorporating the component into a finished assembly.

[0018] In one implementation, the method comprises automatically determining, e.g. by computer post-processing of obtained ESD event data, a risk of failure, after the completion of at least one pick and place mounting job for placement of components on a workpiece but before incorporation of the workpiece into a larger assembly, by comparing a recorded measurement value associated with at least one ESD event recorded during the at least one pick and place mounting job with a predetermined threshold value and further identifying, e.g. by automatically discarding, components and/or workpieces that have been subjected to the at least one ESD event based on the comparison, thereby avoiding

incorporation of workpieces carrying components that have become defect due to an ESD event during the component mounting.

[0019] In one implementation, the method comprises repositioning of the electro- static discharge sensor or sensors in tandem with movement of the component mounting head. By having the ESD sensor(s) following the component mounting head, the number of ESD sensors, and/or their detection range can be limited. Furthermore, determination of properties of the ESDs is facilitated since the distance between the ESD sensor and the ESD event is kept approximately constant.

[0020] In one implementation of the method, monitoring and detection is performed from an opposite side of the workpiece than the side where the component mounting head is located. Thereby the freedom of positioning the ESD sensor(s) is increased.

[0021] The technology disclosed can be practiced in a component mounting device for pick and place mounting, which includes a component mounting head configured to pick and place mount components on a workpiece, such as a circuit board; and at least one electro- static discharge sensor configured to detect electro-static discharge events during mounting of the components. This device as well as implementations thereof exhibit advantages corresponding to those provided by the corresponding method and its implementation described above. Optionally, this instrumented pick and place device can be paired with a processing device that analyses the ESD data, identifies actionable events and recommends or initiates corrective actions. In one implementation, the processing device may analyse the ESD data, further automatically identify actionable events and automatically, without any intervention by the operator, recommend or initiate corrective actions and/or even

automatically discarding a component or workpiece without any intervention by the operator. In one implementation, the technology disclosed above can be practiced in a system including the device and a processing device for processing ESD data.

BRIEF DESCRIPTION OF THE DRAWINGS [0022] FIG. 1 shows an example of a component mounting device; [0023] FIG. 2 is a schematic perspective view of an example of a mounting head;

[0024] FIG. 3 is a schematic perspective view of a part of an implementation of a component mounting device according to the present invention;

[0025] FIG. 4 is a schematic perspective view of a part of another implementation of a component mounting device according to the present invention; and

[0026] FIG. 5 is a block diagram of an implementation of a system according to this invention. DETAILED DESCRIPTION [0027] The following detailed description is made with reference to the figures. Preferred implementations are described to illustrate the technology disclosed, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows.

[0028] The technology disclosed relates to discovering potentially device-killing electro-static discharge (ESD) events occurring in conjunction with device placement or mounting processes. In particular, it relates to use of ESD sensors during component mounting on a circuit board by means of pick and place mounting. Particular aspects of the technology disclosed are described in the claims, specification and drawings.

[0029] The technology disclosed relates to the detection/recording and/or registration of ESD events and an identification of placed components on a workpiece that were exposed to the detected ESD events and where the ESD events are caused by or at least occurs during the placement of the components on the workpiece. In the following the workpiece will be exemplified with a circuit board, and more particularly a PCB.

[0030] The technology disclosed may be practiced as a device incorporated into a system or as a method of detecting defect assemblies of electronic devices. As a device, it includes an ESD sensor in proximity to a device placement head, combined with sensor monitoring hardware and software. Another device implementation positions one or more ESD sensors on an opposite side of a circuit board from a device or component placement head. An array of these sensors may be part of a stage used to support the circuit board. As a method, it includes sensing and recording ESD events, which may be combined with analysis and testing. [0031] The technology disclosed may be used to improve the device mounting processes and, more generally, to prevent unexpected device failure due to ESD events during board assembly. Reduced manufacturing costs and improved rework flows may result.

[0032] The problem of coupling a measured ESD event to a certain component already placed on a circuit board in electronic assemblies is addressed by measuring during placement of the components on circuit boards by using one or more ESD sensors within operative range of a component mount head and detecting the ESD events during the placement and/or mounting of the components.

[0033] The technology disclosed suggests placing an ESD sensor in the electronic component assembly process equipment close to the component place position and monitoring the ESD events together with the component assembly event in such a way that the ESD event is linked to the component mount event. This information will be stored in a database to enable analysis of needed corrective actions.

[0034] The technology disclosed may be used in a method of identifying components in electronic assemblies that have been exposed to electro-static discharge events, including the steps of: during placement of a component on a circuit board, using one or more electro-static discharge (abbreviated ESD) sensors within operative range of a component mount head; and

detecting ESD events during placement and/or mounting of the component.

[0035] The method further includes recording occurrence of the ESD event and recording the strength of the ESD event and at least one of the component being placed or mounted or a position of the mount head when the ESD event happened.

[0036] The method may further include subjecting at least some identified circuit boards to early testing, before incorporation of the circuit boards into larger assemblies, based on the analysis of the ESD events and/or subjecting at least some identified circuit boards to rework based on the analysis of the ESD events.

[0037] In one implementation of the invention, the device and method further includes repositioning the ESD sensor in tandem with movement of the component mount head. [0038] In one implementation of the invention, the device and method further includes using a plurality of the ESD sensors positioned on an opposite side of the circuit board from the component mount head.

[0039] In one implementation of the invention, the method for and device may be configured to both repositioning an ESD sensor in tandem with movement of the component mount head and using a plurality of the ESD sensors positioned on an opposite side of the circuit board from the component mount head.

[0040] As schematically shown in Fig. 1 , an example component mounting device, or machine, comprises a machine frame 1, a component feeding device 3, including a plurality of component feeders, and arranged at a component feeder area of the machine frame 1 , a gantry system 5 having a first beam, or X beam, 7, and a second perpendicular beam, or Y beam, 9, attached to the machine frame 1 , a component mounting head 11 movably attached to the X beam 7, and a board transportation system 13, attached to the machine frame 1. The component feeding device 3 presents electronic components to the mounting head 11. The board transportation system 13 transports substrates between a conveyor line and a working area of the component mounting machine. The mounting head 11 is movable along the X beam 7 and the X beam is movable along the Y beam 9. Thereby, the gantry system 5 makes it possible to move the mounting head 11 between the component feeding device 3 and the substrate. Further, the mounting head 11 is movable in the vertical direction, and is also able to rotate around a vertical axis. It also contains a suction device. This makes it possible to pick up, by activating the suction device, electronic components from the component feeding device 3, transport them to the substrate, and release them at a precise location on the substrate. During the transport from pick up to the substrate a vision centering device 15 may be passed to get an accurate position of picked components.

[0041] An example component mounting head 300, as shown in Fig. 2, comprises a mounting head body 301 , a vacuum controller 303, rotatably attached to the mounting head body 301 , a rotatable nozzle holder 305 comprising a nozzle selection unit 307 attached to the vacuum controller 303, and a nozzle guide 309, which is rotatably carried by a vertically movable frame element 31 1, and a plurality of nozzles 313, held by the nozzle holder 305. The nozzle guide 309 is vertically movable by means of the frame element 311, while the nozzle selection unit 307 is vertically fixed. [0042] When starting to pick components the vertically movable frame element 31 1 is in its upper position where nozzles 313 are selected using the nozzle selection unit 307.

Before vertical movement for component pick up the nozzle holder 305 is rotated to a desired angle. Nozzles to be used are then released in the vertical direction using the nozzle selection unit 307. Selected nozzles will follow the vertical movement of the movable frame element, or Z-frame. When the Z-frame moves down a movement detector (not shown) will sense whether any nozzle 313 is stopped. The downwards movement of the Z-frame 311 will be stopped when one or more nozzles 313 get mechanical contact with a component 327, depending on whether it has been determined that one or more nozzles 313 are going to be used for lifting the component (components). When a nozzle is stopped the related vacuum valve, included in the vacuum controller 303, activates and one or more components are sucked onto one or more nozzles. Picking multiple components can be performed

simultaneously or in separate sequences. Picking one component 327 can be performed using one or more nozzles, and can be synchronized with a nozzle group synchronizer. When picking is done, the mounting head 300 is moved horizontally to the placing area above the circuit board with all components vertically lifted. During this movement the position of picked components will be detected to get a correct mounting position of each component. Placing is performed in a similar way as picking, but including releasing the component(s) on the circuit board instead of picking them.

[0043] The problem of discovery of damaged component devices in electronic assemblies is addressed during placement of the components on circuit boards by using one or more ESD sensors within operative range of a component mount head and detecting ESD events during the placement and/or mounting of the components.

[0044] The problem of unexpected device failure resulting from events during component device placement onto circuit boards is addressed by using one or more ESD sensors within operative range of a component mount head and recording ESD events. This may be enhanced by analyzing the recorded ESD events and identifying assemblies at risk of device failure due to the ESD events. It may be further enhanced by testing at least some of the identified assemblies and/or reworking the identified assemblies.

[0045] Random ESD events during production can cause immediate defects or potential future defects in electronics that lower the quality of the objects produced. When producing electronics used by the aerospace, medical or defense industry, high quality is extremely important and improving the quality is valuable.

[0046] Random ESD events during the electronic component assembly process can be monitored. Then a later step in production could combine information about the ESD event with the knowledge of the ESD sensitivity of the specific component being assembled or the ESD sensitivity of the component already assembled to decide if a corrective action is needed.

[0047]

We disclose placing an ESD sensor in the electronic component assembly process equipment close to the component place position and monitoring the ESD events together with the component assembly event in such a way that the ESD event is linked to the component mount event. This information will be stored in a database to enable analysis of needed corrective actions.

[0048] In one implementation of the component mounting device 50 it comprises a component mounting head 52 for pick and place mounting components 60 on a circuit board 58. The component mounting head 52 can be of the kind described above or some other suitable kind. In Fig. 3 the component mounting head 52 is shown most schematically. At least it comprises one or more nozzles 54, by which it is able to pick components at a components feeding location and place them on the circuit board 60. Reference numeral 56 denotes a picked up component, which is being moved to its mounting position on the circuit board 60. The component mounting device 50 further comprises an ESD sensor 62 having a sensor head 64.

[0049] The ESD sensor 62 is either attached to or repositioned in tandem with the component mounting head 52, close to the ESD sensitive component 56. When the component 56 is being mounted on the circuit board, e.g. a PCB, and an ESD event occurs it is monitored with the ESD sensor 62. Sensing of ESD events can be coordinated with a program or controller that guides the operation of the component mounting head, so that the component 56 being placed and the location of the mount head at the time of any recorded ESD event will be known. Recording of ESD events can be combined with recording of sensitive components involved and/or a location of the mount head at the time of the event. For that matter the component mounting device 50 comprises a recording device 68, see Fig. 5, which is configured to record inter alia occurrence of ESD events and ESD properties, and which is connected with the ESD sensor(s) 62.

[0050] The ESD sensor can be of any known type, such as ESD detector disclosed in

US 7821751 which includes detector circuitry and a detector antenna structure, which corresponds to the sensor head 64 shown in Fig. 3. The detector antenna detects the radiated energy which is present in an electric field when an ESD event occurs. The detected energy is interpreted as an ESD event signal by the detector circuitry.

[0051] Another example of an ESD sensor is the "ESD Pro Event Detector" marketed by 3M Company.

[0052] In another implementation of the component mounting device 50, the ESD sensor 62 is attached under the workpiece 58, e.g. PCB. When the ESD sensitive component 56 is mounted on the workpiece 58 by the mounting head 52 and an ESD event occurs it can be monitored with the ESD sensor 62.

[0053] In either application, multiple sensors 62 could be used. With three or more sensors, the location of an ESD event could be triangulated. For the under PCB

implementation, more sensors might be used to eliminate any need for sensor movement. The sensors 62 could be embedded in a stage that supports the PCB 58 during component placement. For the sensor on mounting head implementation, it could be assumed that ESD events would flow over or through the mounting head, given its proximity to the circuit board 58. This could make it unnecessary to rely on multiple sensors, other than for redundancy.

[0054] Multiple ESD sensors 62 could be mixed between positioning over and under the PCB 58.

[0055] Statistical quality control testing is sometimes used during production. That means that less than all sub-assemblies or final assemblies are tested. Moreover, tests may be more or less exhaustive, as testing time has a measurable cost.

[0056] Recording of an ESD event may be used to identify subassemblies or final assemblies to test. It can be used to select subassemblies for testing prior to final assembly. It can be used to select how extensively to test. For example, some ESD events may trigger stress testing, beyond normal functional testing.

[0057] Over time, statistical analysis of recorded ESD events and results of testing can be modeled and relationships between ESD event strength and failure of particular components or component types can be determined. Then, identification of subassemblies or final assemblies to test, to test prior to final assembly or to test extensively can be a function of ESD event strength and component or component type.

[0058] The technology disclosed may be practiced as device incorporated into a system or a method of protecting assemblies of electronic devices.

[0059] The specification describes technologies that can be applied to discovering, predicting or guarding against damaged component devices in electronic assemblies.

[0060] In general, one aspect of the technology described can be embodied in methods that include the actions of, during placement of a component on a circuit board, using one or more ESD sensors 62 within operative range of a component mount head; and detecting ESD events during placement and/or mounting of the component. By operative range, we mean that the ESD is effective from where it is positioned to sense ESD events taking place between the component mount head and the workpiece, e.g. PCB. An array of ESD sensors is considered to be within operative range if at least one of the sensors is in operative range of the event. Other implementations of this aspect include corresponding systems, apparatus, and computer program products.

[0061] Different implementations of the method optionally include one or more of the features of the following implementation. The actions may be repeated for a plurality of components 60 on the same circuit board 58. The occurrence of the ESD event is recorded. Recording includes different properties of the ESD event, such as a strength of the ESD event and an identification of at least one of the components being mounted, or a position of the mounting head 52 when the ESD event happened, or both. The recorded ESD event properties are then analyzed to identify circuit boards 58 at risk of failure due to the ESD events. At least some identified circuit boards 58 are subjected to stress testing based on the analysis of the ESD events. At least some identified circuit boards 58 are subjected to testing, called early testing, before incorporation of the circuit boards 58 into larger assemblies, based on the analysis of the ESD events. At least some identified circuit boards 58 may be subjected to rework based on the analysis of the ESD events. Other implementations of these features may include corresponding systems, apparatus and computer program products. [0062] According to an implementation of a system 70, as shown in Fig. 5, it comprises the component mounting device 50, and a processing device 72, which is connected, wireless or by wire, with the recording device 68 described above.

[0063] The processing device 72 may be configured to analyze the detected and/or registered ESD events and to determine which of the components placed on the workpiece that were exposed to an ESD event that may lead to that those identified components no longer function properly. The processing device 72 may further be configured to provide, e.g. to an operator, a report of the detected/registered ESD events and/or a report identifying the placed components that might have been damages by an ESD event during the placement operation.

[0064] The processing device is configured to analyze the ESD properties, which it receives from the recording device 68, and to determine, on basis of the analysis, whether or not the corresponding circuit board 58 is at risk of failure.

[0065] According to different implementations of the present invention the strength of the ESD event is measured, and compared with a threshold. If the strength exceeds the threshold it is decided that there is a risk of damaged components, and the circuit board is subjected to post-processing. The post-processing can include different subsequent, and/or alternative steps, such as troubleshooting the circuit board in order to discover any damaged components and either replacing them or discarding the whole circuit board, or simply discard the circuit board in the first place without troubleshooting. The post-processing can be done at the production site, in line with the production or off line, or at some other location before the circuit board is to be mounted in a device, etc.

[0066] Thus, in one example, the present method includes testing, by means of for instance the processing device 72, a component determined to be subject to an electro -static discharge, approving the component as tested and incorporating the component into a finished assembly.

[0067] In another example, the present method includes testing, by means of the processing device 72, a component determined to be subject to an electro-static discharge, requiring rework of the component tested and incorporating the reworked component into a finished assembly. [0068] In yet another example, the present method includes monitoring a component during pick and place assembly, approving, by means of the processing device 72, the component as not having been subjected to electro-static discharge during assembly, and incorporating the component into a finished assembly.

[0069] According to an implementation of the mounting head, the ESD sensor is fully integrated with, or assembled with, the mounting head. Thus, the ESD sensor automatically moves along with the mounting head.

Claims

CLAIMS 1. A method of discovering a risk for damaged components in electronic assemblies, including:

at a component pick and place mounting device, monitoring a mounting of a component on a workpiece, such as a circuit board, by means of at least one electro-static discharge sensor arranged at the device; and

detecting electro-static discharge events during said mounting of the component.

2. The method according to claim 1 , comprising repeating said monitoring and detecting for a plurality of components being mounted on the same circuit board.

3. The method according to claim 1 or 2, further including recording occurrences of the electro-static discharge events.

4. The method according to any one of claims 1-3, further including, for each electro- static discharge event, recording properties of the electro -static discharge event comprising: recording a strength of the electro-static discharge event; and

recording at least one of an identification of the component presently being mounted and a position of the mounting head at the occurrence of the electro-static discharge event.

5. The method according to claim 3 or 4, further including analyzing the properties of at least one of the electro-static discharge events; and

determining, on basis of said analysis, whether or not the corresponding circuit board is at risk of failure.

6. The method according to claim 5, further including subjecting a circuit board determined to be at risk of failure to stress testing.

7. The method according to claim 5 or 6, further including subjecting a circuit board determined to be at risk of failure to testing before incorporation of the circuit board into a larger assembly.

8. The method according to any one of claims 1-7, further including repositioning of said at least one electro-static discharge sensor in tandem with movement of the component mounting head.

9. The method according to any one of claims 1-8, said monitoring further including using at least one electro-static discharge sensor positioned at an opposite side of the circuit board from the component mounting head.

10. The method according to any of claims 1-9, further including testing a component determined to be subject to an electro -static discharge, approving the component as tested and incorporating the component into a finished assembly.

11. The method according to any of claims 1 -9, further including testing a component determined to be subject to an electro-static discharge, requiring rework of the component tested and incorporating the reworked component into a finished assembly.

12. The method according to any of claims 1-9, further including monitoring a component during pick and place assembly, approving the component as not having been subjected to electro-static discharge during assembly and incorporating the component into a finished assembly.

13. A component mounting device for pick and place mounting, including:

a component mounting head configured to pick and place mount components on a circuit board; and at least one electro-static discharge sensor configured to detect electro-static discharge events during mounting of the components.

14. The device according to claim 13, comprising a recording device configured to record occurrence of electro-static discharge events and connected with said at least one electro- static discharge sensor.

15. The device according to claim 14, wherein the recording device is configured to record properties of each electro-static discharge event including a strength of the electro- static discharge event, and at least one of an identification of the component presently being mounted and a position of the mounting head at the occurrence of the electro -static discharge event.

16. A system including the device according to claim 13, comprising a processing device connected with the recording device, and configured to analyze the properties of at least one of the electro -static discharge events; and determine, on basis of said analysis, whether or not the corresponding circuit board is at risk of failure.

17. A system including the device according to claim 13, comprising a processing device connected with the recording device, and configured to analyze the properties of at least one of the electro -static discharge events; and determine, on basis of said analysis, whether or not to subject the corresponding circuit board to testing before incorporation of the circuit board into a larger assembly

18. The device according to any one of claims 13-15, said at least one electro -static discharge sensors being movable, wherein the movement is coupled in tandem with movement of the component mounting head.