Zulki's PCB Nuggets: Cleanliness is Next to Reliability

Today’s PCBs are highly populated with increasingly smaller device packaging. As a result, these advanced device packages are extremely difficult to clean due to tight densities and configurations, especially with bottom terminated components.

Current OEM system designs, and those on the drawing board, are driving these newer technologies, which are the foundation of advanced PCB assembly and manufacturing.

Against this backdrop, cleaning processes—as a major part of PCB assembly and manufacturing—take on new meaning. Cleanliness in manufacturing plays a major role, now more than ever, to not only perform optimal assembly, but also to achieve high reliability. This can come in handy when we are talking about Mil/Aero projects.  

However, calibrating cleanliness to comply with new technology advances is one area that is often taken for granted. Consequently, prudent OEMs, especially those dealing in Mil/Aero and RF/Microwave applications, must pay special attention to this particular area as their advanced products undergo PCB assembly and manufacturing.

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Let’s take a step back and consider all those fluxes, pastes, and adhesives we use on a daily basis on the assembly floor. In most instances, after undergoing those processes a PCB retains some residues from those materials. Those remaining residues, however miniscule, must be properly cleaned. Figure 1 shows the flux and paste residues under a device.

Why is that important? Think about those bottom terminated devices like BGAs, QFNs, and DFNs, among others. You cannot physically see flux or paste residue in those hidden device areas. If even the smallest residue gets stuck in those vulnerable device areas, they can create issues and challenges along the assembly path.

This risk is especially true if you are using very fine pitch BGA, QFN, and DFN devices. Let’s say some residues are left in those bottom terminated areas. As a result, it will be difficult–to nearly impossible–to perform underfill for those devices. Leftover flux and paste contamination across different QFN and DFN balls and bumps does not allow enough room for underfill material to go in and secure those devices.

Those devices must be properly cleaned. If not, because these are active fluxes, there’s a high probability of creating corrosion or contamination; the fluxes have active ingredients which trigger that contamination or corrosion over time. In short, that creates reliability issues during assembly and later on in the field as latent failures.

PCB cleanliness is especially critical for Mil/Aero and RF/microwave applications. Mil/Aero, in particular, demands stringent compliance with such standards as Military Standard (MIL/STD) 1246C. In part it says, “This standard provides a basis and a uniform method for specifying product cleanliness levels and contamination control program requirements. The emphasis is on contaminants that cause damage through physical interactions rather than chemical interactions.”

RF and microwave applications also require stringent cleaning processes to maintain specified reception and transmission signal speeds. If these products are not cleaned properly, and residues remain there, the speed of these extremely high-speed signals do not travel at optimal levels. As a result, higher than normal signal to noise ratio (SNR) is generated, which is not desirable. Furthermore, residues deteriorate signals and signal propagation, thereby making these products less than optimal.

What is Cleanliness, How is It Done, and How Do We Measure It?
There are multiple aspects to cleanliness, defined by IPC class 2 or class 3. Typically, every single board assembled with water soluble flux goes through deionized (DI) water cleaning, which is standard process for board cleaning after the assembly is complete. Here, it’s highly important to control the washer’s different parameters. What is the water temperature? What is the flow of that water pressure? And what is the conveyor speed on which the board is going through to make sure that your cleanliness is properly performed?

With standard cleaning, you have to make sure to review, examine, and calculate for the optimal cleaning to be performed. In a second category of cleaning, there are cases where DI water cannot perform all the cleaning.  Or, perhaps, there are certain components on the PCB that water can damage.

In cases like these, special chemistry (saponifiers) and batch cleaning processes are used for cleaning. A saponifier, also known as an aqueous cleaner, is formulated to remove resin, rosin, no-clean and water-soluble flux residues. 

Also, during batch cleaning, you need to assure that water is not touching certain components as specified in their datasheets. Your choice of batch cleaning techniques with saponifiers and different chemistries depends on a PCB’s application and the type of components on a board. Batch cleaning is a slower process compared to DI water because it isn’t as automated as the inline washer process.

As I’ve said here, DI water is the industry standard cleaning process. Both DI water and batch cleaning are used for Mil/Aero and RF/microwave PCB applications. However, Ionographic testing is required to determine how clean those PCB are which is done by performing measurements on the purities of the board.

The IPC standard for cleanliness is equivalent of 10 micrograms per inch squared of sodium chloride (10µg/in2 of NaCl). That standard is now outdated. Current cleanliness requirements, especially for fine pitch devices are in the range of 2 to 3 mg NaCl equivalent/in2. This measurement is also a process control indicator at an EMS company.

Once the PCBs are cleaned, it may be necessary to further measure the cleanliness level, especially in case of RF and Mil/Aero applications. For this, Ionograph contamination tester comes in handy. It measures the purity of a board, say for example, 99.99% purity or 95.75% purity. So, it gives us a specific quantifiable number, which cannot be challenged or disputed. And that is typically required for extra clean boards that are required either in Mil/Aero or RF/microwave applications.

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

 

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2021

Zulki's PCB Nuggets: Cleanliness is Next to Reliability

12-09-2021

Today’s PCBs are highly populated with increasingly smaller device packaging. As a result, these advanced device packages are extremely difficult to clean due to tight densities and configurations, especially with bottom terminated components. Current OEM system designs and those on the drawing board are driving these newer technologies, which are the foundation of advanced PCB assembly and manufacturing.

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Zulki’s PCB Nuggets: Thermal Compression Bonding for Extra Fine Pitch Flip Chips

10-20-2021

Medical OEMs and others moving toward developing and producing small, portable products may want to investigate the emerging technology of thermal compression bonding or TCB. TCB is ideally suited for miniature products that use fine pitch flip chip devices undergoing PCB microelectronics assembly.

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Zulki’s PCB Nuggets: WBAN Steps Into PCB Microelectronics Assembly

09-15-2021

A new miniature wireless network is stepping out of academic journals, into micro-miniature medical device applications, and subsequently onto the PCB microelectronics assembly floor.

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Zulki’s PCB Nuggets: Photonics Comes to PCB Microelectronics Assembly

08-11-2021

Photonics has been around for many years. Today, that technology is beginning to make its presence known in PCB microelectronics assembly and in a variety of new applications. But we need to step back a bit and revisit reasons why photonics is so vital to meet today’s demands for increasingly higher speeds in advanced systems.

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Zulki’s PCB Nuggets: Sub-Micron Die Bonding—Don’t Be Misled by Five Micron Placement Standard

07-14-2021

It is critical for an EMS company or microelectronics service provider to have the capabilities to design, define, implement, and assemble sensor, biosensor, and MEMS device placement with sub-micron accuracy. Not only should they be able to do that with high accuracy, but also, they should be able to quantitatively verify that accuracy.

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Zulki’s PCB Nuggets: Meet the New Player in PCB Microelectronics Assembly—Interposers

06-09-2021

Today, everything is shrinking and getting smaller, as I have written about in earlier columns. Now, a new player is coming in to help make PCB real estate more available on small flex and flex-rigid circuits undergoing microelectronics assembly. That new entrant is an interposer, which is a type of connector that takes connections from one side of the substrate or board or material to the other side.

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Zulki’s PCB Nuggets: How Effective Is Your PCB Microelectronics Assembly?

05-05-2021

There is a good chance that all PCB microelectronics assembly and manufacturing processes are not created equal. In today’s day and age, that can be a major issue for medical OEMs who are now in the midst of developing or producing their newly advanced miniature medical products.

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Zulki’s PCB Nuggets: Five Key Benefits for Onshoring PCB Microelectronics Assembly

04-06-2021

There are five key benefits to U. S. OEMs for onshoring PCB microelectronics assembly and manufacturing, but this discussion is prefaced by this fact: the future lies in PCB microelectronics assemblies compared to traditional SMT assemblies.

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Zulki's PCB Nuggets: Onshoring for PCB Microelectronics Production?

03-04-2021

Many OEMs may not be aware that here in the U. S., microelectronics assembly and manufacturing is leading in technology advances and provides OEMs a relatively easier way to bring that production back to the U. S. compared to on shoring PCB SMT production.

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Zulki's PCB Nuggets: Take a Deep Dive Into U.S. Medical Device Production

01-27-2021

There are new angles, new thinking emerging for medical OEMs to consider in order to keep production in the U. S. versus overseas. The foremost thinking (biggest challenge) associated with those angles focuses on whether the product can be produced cost effectively in a timely fashion, so it’s distributed in the supply chain for a given medical device OEM.

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2020

Zulki’s PCB Nuggets: Wire Bonding and CoB for PCB Microelectronics Assembly

12-09-2020

Real estate continues to be a precious commodity for substrates, package sizes, dies, and PCBs. But now, the industry is taking another stab at further reducing PCB real estate. Zulki Khan examines wire bonding and chip on board (CoB) to point out what might be best for your medical electronics device while undergoing PCB microelectronics assembly.

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Zulki’s PCB Nuggets: Consider Low-Temp Solder for PCB Microelectronics Assembly

11-11-2020

With newer, smaller devices coming on the market, EMS providers and contract manufacturers (CMs) must adjust their PCB assembly technologies to comply with these demands. Zulki Khan details how thermal profiling and the use of the correct solder paste become an even more critical step than before in conventional SMT and the newer microelectronics assembly.

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Zulki’s PCB Nuggets: What’s Different Between C2 and C4 for PCB Microelectronics Assembly?

10-21-2020

In Zulki Khan's last column he talked about flip-chip ball grid array (BGA), or FCBGA, making its grand entrance into PCB microelectronics assembly. But that subject requires a lot more digging to get the full story for OEMs planning highly advanced products that demand PCB microelectronics assembly. In that regard, C4 and C2 bumps for flip-chip assemblies are among the top techniques that require close attention.

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Zulki’s PCB Nuggets: FCBGA Packaging Enters PCB Microelectronics Assembly

09-09-2020

The demand for smaller circuitry and packaging, as well as ever-shrinking PCB real estate, have continually pushed PCB assembly and manufacturing protocols. Part of these technological advances involves a combination of flip-chip and BGA (FCBGA) packaging. Zulki Khan explains the importance of FCBGAs.

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Zulki’s PCB Nuggets: DOEs on Call for New Wearable Medical Devices

08-05-2020

Zulki Khan explores how biosensors for human-machine interfaces (HMIs) and new, flexible electrodes are leading the way, are among the most recent developments and promise more sophisticated medical wearable devices for health monitoring.

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Zulki’s PCB Nuggets: Soft Electronics Pose PCB Microelectronics Assembly Challenges

07-08-2020

Zulki Khan explains how PCBs have moved from traditional large rigid boards to considerably smaller rigid and combinations of rigid and flex circuit boards, even to the point that bare chips and wire bonding are used during the PCB microelectronics assembly of these tiny boards.

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Zulki’s PCB Nuggets: Medical Miniaturization and PCB Microelectronics Assembly

06-24-2020

Medical electronics continue to be a gamechanger, with miniaturization being foremost today in the minds of medical OEMs. Zulki Khan discusses how there is a growing demand for even greater device and component miniaturization that plays a major role in the PCB microelectronics assembly of these medical devices today.

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Zulki’s PCB Nuggets: Add Hi-rel to ISO 13485 for More Robust Ventilator PCBs

05-13-2020

It's important to meet FDA and ISO 13485 standard quality and reliability requirements for ventilators and other medical equipment. Zulki Khan explains how there’s still more that ventilator OEMs need to put into practice, specifically in the high-reliability or “high-rel” area to further add to ISO 13485.

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Zulki’s PCB Nuggets: Urgent Call for Ventilators—PCB Technology at the Ready

04-15-2020

An urgent call is out to medical equipment makers that thousands—even millions—of ventilators are in the greatest demand in our history due to the worldwide COVID-19 outbreak. Zulki Khan explains how new ventilator makers—as well as traditional ones—must weigh a number of key PCB design, assembly, and manufacturing factors.

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Zulki’s PCB Nuggets: Putting the Heat on for Thermal Profiling

03-11-2020

A unique thermal profile is designed for each PCB job undergoing conventional SMT assembly, as virtually every PCB assembly professional knows. But what about a PCB assembly project involving both conventional rigid board and an extraordinarily small rigid or rigid-flex circuit undergoing microelectronics assembly? Zulki Khan covers PCB hybrid assembly, which requires two separate, unique, and distinctly different thermal profiles.

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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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