Zulki’s PCB Nuggets: PCB Microelectronics—Inspection and Calibration

Microelectronics manufacturing is the companion of SMT manufacturing and forms PCB hybrid manufacturing. Tools for SMT manufacturing have been around for a long time and have proven their value. Now, with microelectronics, new and different types of high-powered laser microscopes are populating the microelectronics assembly and manufacturing area to provide highly effective inspection and calibration.

Scopes like the Keyence VK-X 1000 are giving microelectronics customers assurances that substrates and dies are intact during incoming inspection as well as post-assembly verification (Figure 1). Plus, they are precisely calculating measurements. They are also taking highly accurate readings for the specific height, length, and width of wire bond loops and curvatures to make sure specifications are met, as defined in the scope of work.

NexLogic-Fig1-17Jul2019.jpg

Figure 1: High-powered laser microscope.

Inspection tasks include die, epoxy resin and solder mask bleeding, and air bridge. Calculations include length, width, and height in the Z-axis. Also, these scopes create 3D rendering, making the images more vivid.

Microscopes inspect the die surface for defects. Those can be surface anomalies, any type of damage—such as fine cracks, tiny die corner chipping, corrosion, contamination, or oxidation. In this case, die inspection is expected to meet MIL-STD 883 Revision G or E.

The possibility of epoxy resin and solder mask bleeding is inspected as well. At times, misjudging the amount of epoxy under the die for die attach leads to a floating die. That is definitely not desirable. The high-powered laser microscope verifies that the die is 100% on a substrate’s or interposer’s base, creating perfect joints.

As for solder mask bleeding, the mask may bleed onto the pad where wire bonding is to be installed. The issue is the pad’s surface may not be sufficient in size to perform the bonding. Again, these scopes inspect and verify this issue doesn’t exist.

Other times, flux or epoxy residues may create similar issues. If PCB hybrid manufacturing—meaning a combination of SMT and microelectronics manufacturing—is being performed, some residues may be leftover from SMT manufacturing. Those residues may remain on a PCB’s substrate or creep into areas where microelectronic components are to be placed. As a result, the surface becomes uneven or unfit for die attach or wire bonding. When this occurs, the bond to be created at the wire bond pad becomes difficult if not impossible.

Therefore, cleanliness is of the utmost essence. The thinner the wire bond is, the more precise the pad needs to be. Typically, thin wires used for the pad are extremely close to one another. If the thinnest or finest 7/10 of a mil wire is used, the surface needs to be as clean as possible by applying either alcohol, isopropyl alcohol (IPA), or argon gas for extra cleanliness.

They also inspect air bridges. An air bridge is the air distance created to bypass a component located between two other components. That’s done to connect a wire bond from one point to another and overpassing the middle component.

Moreover, aside from inspections, these microscopes calculate length, width, and height in the Z-axis for dealing with height restrictions of dies and substrates. Sometimes, dies are attached in an ENIG or ENEPIG surface finish-based cavity. Dies need to be very precisely height controlled. This permits perfect fit in those cavities before wires can be attached via wire bonding after die attach. The high-powered scopes are perfect tools to view cavity depth as well as to perform height measurements in the Z-axis.

Finally, 3D rendering of the pads, substrate height, or paste height provide microelectronics manufacturing technicians a visual. This allows them to calculate the distance between the substrate and the wire bonding as well as check the thickness of the epoxy or the solder paste that is being used.

It is absolutely essential to calculate intricate fine wire bond loops and curvatures for some projects. For example, a 3D profile is created for a wire bond loop’s 5-µm accuracy in measuring the height. In this 3D profile, various aspects can be viewed. Those include die and epoxy thickness and distance between the substrate or interposer and die. Creating this 3D profile gives a very clear-cut picture, which can easily be precisely measured. It also provides a very good visual, which is used as a proof of effective versus poor microelectronics assembly.

In summary, there are certain PCB manufacturing aspects that even the finest X-ray devices cannot look at precisely, whereas these high-powered inspection tools come into play to deal with intricate details to perform perfect microelectronic assembly.

Zulki Khan is the president and founder of NexLogic Technologies Inc.

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2019

Zulki’s PCB Nuggets: PCB Microelectronics—Inspection and Calibration

07-18-2019

Microelectronics manufacturing is the companion of SMT manufacturing and forms PCB hybrid manufacturing. Tools for SMT manufacturing have been around for a long time and have proven their value. Now, with microelectronics, new and different types of high-powered laser microscopes are populating the microelectronics assembly and manufacturing area to provide highly effective inspection and calibration.

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Zulki’s PCB Nuggets: Three Die Attach Methods for Microelectronics Manufacturing

06-27-2019

Die attach technology is increasingly being applied in PCB hybrid manufacturing (i.e., combining traditional SMT manufacturing with microelectronics) to comply with the requirements of small PCBs, especially rigid, flex, and combination rigid-flex circuit boards. These smaller boards are used in a variety of IoT, wearable, and portable applications.

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Zulki’s PCB Nuggets: Consider the Integrity of Wire Bonding

06-12-2019

While reliability and integrity can be regarded as synonymous as far as PCB manufacturing with microelectronics assemblies is concerned, the integrity of wire bonding—the methodology of interconnecting the wire to the bond pad—takes on other reliability-associated process qualities. Here are three factors that need to be implemented to create the integrity of wire bonding.

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Zulki’s PCB Nuggets: Avoid PCB Wire-bond Loop Failures

05-30-2019

Today, hybrid PCB manufacturing is making greater inroads into our industry, which is the marriage of traditional SMT manufacturing together with microelectronics and wire bonding. In many cases, the OEM working with EMS providers doesn’t fully understand the nuances of effective wire bonding and related failures.

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PCB Hybrid Manufacturing: Coming Your Way

05-15-2019

Today, PCB manufacturing is rapidly evolving to include SMT as well as microelectronics, such as chip-on-board (CoB) installation, flip-chip assembly, wire bonding, and die attach. SMT merged with microelectronics is also known as hybrid manufacturing. This is occurring because PCBs have begun shrinking at a faster pace in recent years due to the introduction of wearables, IoT devices, and portables demanding smaller circuit boards.

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2014

Tighter Scrutiny Needed for PCB Cleaning Agents

05-13-2014

PCB cleanliness on the assembly floor is now getting more attention, due to tiny residues and contaminants being left on assemblies after new, advanced assembly processes. Cleaning methodologies, testing, analysis, and special chemistries are being taken to a new level to assure customers of ultraclean boards to avoid costly latent issues.

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Zulki's PCB Nuggets: Tighter Scrutiny Needed for PCB Cleaning Agents

05-13-2014

PCB cleanliness on the assembly floor is now getting more attention, due to tiny residues and contaminants being left on assemblies after new, advanced assembly processes. Cleaning methodologies, testing, analysis, and special chemistries are being taken to a new level to assure customers of ultraclean boards to avoid costly latent issues.

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Uncovering Assembly Problems of High-Speed PCBs

03-12-2014

The high-speed board may be perfect when it comes to BGA assembly. All the balls properly collapse; all the thermal profiles are accurately determined and performed. All soak temperatures, pre-heat, soak, and cool-off periods fall within manufacturer limits and ranges. Yet, this high-speed board fails at high speed at the time of system functional level testing in the system.

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Zulki's PCB Nuggets: Uncovering Assembly Problems of High-Speed PCBs

03-12-2014

The high-speed board may be perfect when it comes to BGA assembly. All the balls properly collapse; all the thermal profiles are accurately determined and performed. All soak temperatures, pre-heat, soak, and cool-off periods fall within manufacturer limits and ranges. Yet, this high-speed board fails at high speed at the time of system functional level testing in the system.

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EMS Discovers Mature IC Technologies

01-14-2014

Columnist Zulki Khan asks, "Did you know that really new, up-to-the-moment PCB technologies are nesting on the doorstep of PCB assemblers?" In fact, he says some of these technologies are very mature, but they're completely new to the assembly side of things.

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Zulki's PCB Nuggets: EMS Discovers Mature IC Technologies

01-14-2014

Columnist Zulki Khan asks, "Did you know that really new, up-to-the-moment PCB technologies are nesting on the doorstep of PCB assemblers?" In fact, he says some of these technologies are very mature, but they're completely new to the assembly side of things.

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2013

Another Look at AOI

11-13-2013

PCB inspection is taking on greater significance as boards and packaging become increasingly smaller, with greater functionality. Automated optical inspection (AOI) and its backup associate, X-ray, team up to catch a variety of board assembly problems. But it's AOI that's at the forefront of this process.

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Zulki's PCB Nuggets: Another Look at AOI

11-13-2013

PCB inspection is taking on greater significance as boards and packaging become increasingly smaller, with greater functionality. Automated optical inspection (AOI) and its backup associate, X-ray, team up to catch a variety of board assembly problems. But it's AOI that's at the forefront of this process.

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Zulki's PCB Nuggets: ECOs Reviewed - The Importance of Accuracy

09-11-2013

Designers can perfectly layout a design and, in theory, follow written specifications to the letter, but when one factors in the practicality of that design, virtually everything associated with it has its limitations--ranging from the material used to make the board to assembly, machine tolerances, and process limitations.

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