Zulki’s PCB Nuggets: Vital Details for Implantable Medical Devices

In an earlier column, I discussed ingestible medical devices known as smart pills and smart cameras, and the role PCB microelectronics plays in the assembly and manufacturing of those products. Another segment of the medical electronics devices market is rapidly growing, as well: implantable medical devices, which medical personnel surgically or otherwise insert into various parts of the human body. They range from cardiac pacemakers or blood pressure sensor monitors onto smaller devices implanted into different human organs.

The same additional PCB microelectronics assembly and manufacturing care and attention going toward ingestible medical devices are also critical for implantable medical devices. In particular, the scope of work is of the utmost importance. General guidelines and product requirements must be defined in very specific and detailed work instructions that are associated with every single step in the assembly and manufacturing of an implantable medical device.

Like an ingestible smart pill or smart camera, medical device OEMs have to keep in mind that an implantable medical device is very sensitive since it’s going inside the human body. This means not taking any chances or making any assumptions. This is especially true for PCB SMT and microelectronics assembly and manufacturing in the areas of device handling and cleaning, inspection, and bill of materials (BOM). Keeping a detailed record of each of the steps during the different manufacturing steps is also of utmost importance.

It may sound like an insignificant task, but cleaning takes on greater meaning with devices undergoing PCB microelectronics assembly and manufacturing. Circuit boards like rigid and flex circuits, stiffeners, and dies all must be wiped with isopropyl alcohol (IPA). Guidelines and standard procedures in this particular area should specify the IPA concentration level, such as 70% or 80%. Furthermore, assurances need to be made that IPA strength is properly evaluated for SMT when IPA cleaning is applied to parts, including stiffeners for flex assemblies. Also, humans cannot directly touch some ingestible projects; in cases like this, there are specific requirements, such as wearing latex-free gloves to handle those fixtures and using tooling that is made from stainless steel.

Inspection, BOM, and Microelectronics

Qualified and trained quality control professionals should perform a detailed incoming material inspection to assure that there are no shipping damages. As part of that inspection, incoming materials are checked to make sure they are visually clean and conforming to product quality specified in related documents.

Further, there has to be a checklist for all incoming material. Included is a certificate of compliance (COC) or certificate of analysis (COA). Both need to be available for the inspection process. Also, it’s important to note different devices have different record-keeping time periods. Some require three years of record-keeping and others as many as seven years. If there’s non-conformity in this regard, the OEM customer should be immediately notified.

The BOM should be very specific, complete, and descriptions must be as detailed as possible. For example, a preferred epoxy is listed for a flex circuit, and a detailed description is given. However, if that particular epoxy is not available, then a secondary epoxy should be listed as an alternate.

When it comes to microelectronics, it’s important to note that sensors are increasingly being used. Sensor dies could be MEMS, pressure sensors, or different kinds of sensors, like mechanical vibration sensors. Again, details are vital. Clear and complete descriptions should be provided about the type of epoxy/paste used to attach a sensor die and an ASIC, for example. For wire bonding, details are important for describing the type to be used—whether it’s gold, aluminum, platinum, or copper—and the wire thickness needs to be spelled out, too.

Device encapsulation takes on a different and greater meaning since implantable medical devices are going into the human body. That means encapsulation materials must be carefully selected. In some cases, a conductive ink may need to go over the glob top or encapsulation gel. At times, more than one glob top coating is required, meaning further details need to be specified and carefully implemented at product realization stages.

More Details

There are also a number of other carefully orchestrated details that must be considered and implemented for implantable medical device assembly and manufacturing. For instance, epoxies must be dispensed using highly precise techniques. When certain compounds are to be mixed together, they must be mixed in exact proportion, all the while keeping pot life in mind; after mixing the epoxy, it has to be used within a certain time period. Otherwise, it will dry up or lose its potency.

Further, those compounds need to be in a temperature-controlled environment before, during, and after they are mixed. When curing a conductive epoxy or coating, specific instructions should be given in minutest details, such as curing a specific compound mixture with a curing temperature range and defined time. Even to store the device before or after for an encapsulation epoxy—details like optimal storage temperature, ambient or temperature-controlled—need to be reviewed and implemented, keeping in mind the epoxy’s technical specification datasheet.

When MEMS are used, especially sensors, it’s vital that the sensing membrane is protected for the MEMS since this is the pressure sensor die. If it’s not assembled properly, a malfunction can result. That’s because it is so sensitive that the slightest of vibrations or even when applying wire bonding can adversely affect the membrane, and in worst cases, they can damage the sensing membrane. Sometimes, a glass layer can be placed in the middle of a MEMS device to assure that the pressure sensor is properly protected.

It's also important for the implantable medical device OEM to know that the product undergoes assembly and manufacturing in an ISO Class 100,000 or 10,000 cleanrooms. Moreover, questions have to be raised about ESD control requirements in the cleanroom and SMT floor. There can be devastating effects if cleanroom and SMT floor personnel aren’t properly grounded, humidity isn’t controlled, and ESD is not properly maintained. MEMS devices, sensors, and other key devices can be affected so that they don’t work in an optimal fashion.

Summary

Implantable medical devices in PCB microelectronics assembly and manufacturing demand an extra measure of details compared to conventional PCB SMT assembly and manufacturing.

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

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2019

Zulki’s PCB Nuggets: Vital Details for Implantable Medical Devices

12-04-2019

In addition to smart pills and smart cameras, which Zulki Khan covered in a previous column, another segment of the medical electronics devices market is rapidly growing, as well: implantable medical devices, which medical personnel surgically or otherwise insert into various parts of the human body. Zulki explains the extra measures required for these devices.

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Zulki's PCB Nuggets: Multi-tier Wire Bonding—Diving Into PCB Microelectronics

11-07-2019

As the name implies, multi-tier wire bonding involves several levels of wire bonding beyond the single level of wire bonding, which is traditionally used in semiconductor and/or PCB microelectronics assembly. Here, you have two, three, and four levels of wire bonding, in some cases, called stacked wire bonding. Also, multi-tier wire bonding offers OEMs a solution when the number of inputs/outputs (I/Os) are far beyond the traditional ones that are used in the single wire-bonding application.

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Zulki’s PCB Nuggets: Smart Pills & Cameras—The Next Frontier for PCB Microelectronics

10-23-2019

"Take two aspirin and call me in the morning," is the proverbial, jovial, and often-cited elixir that doctors have prescribed over the years for whatever ails you. Today, medical electronics are adopting the same concept but with new technologies. Now, the phrase, "Take two aspirin," takes on new meaning, as medical electronics move into new frontiers of inspecting a human’s gastrointestinal tract with new, revolutionary ingestible smart pills and "pill cams."

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Zulki's PCB Nuggets: A Better Grasp of Glob Top Epoxy Factors

09-25-2019

In my last column, I cited important aspects of glob top epoxies, calling attention to the fact there are different epoxy manufacturers. In this column, I will continue to emphasize six other important factors of glob top epoxies.

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Zulki’s PCB Nuggets: Get a Handle on Glob Top Epoxies

09-12-2019

Most often, glob top is the prevalent method EMS providers use today. However, the most important point to be made about glob top is the fact that multiple manufacturers are producing different glob top epoxies. And within each manufacturer, there are numerous types of epoxies being produced. Another key point is that EMS providers and contract manufacturers generally are the ones deciding on the kind of epoxy to use. This column will further describe how you can get a handle on glob top epoxies.

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Zulki’s PCB Nuggets: Protect the Die and Wire Bonding for Effective PCB Microelectronics Assembly

07-31-2019

Protecting bare dies on a PCB or substrate is a major process of microelectronics assembly. As we’ve said before, microelectronics assembly and manufacturing work in tandem with traditional SMT manufacturing for complete PCB hybrid manufacturing of today’s smaller form factor products, including IoT, wearables, and portable devices.

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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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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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