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

As I’ve said in earlier columns, the demand for smaller circuitry and packaging, as well as ever-shrinking PCB real estate, have continually pushed PCB assembly and manufacturing protocols. Newer, smaller, portable, and ingestible medical devices are opening new frontiers and are leading OEMs from other industries down that same road.

Part of these technological advances deal with a new twist or turn associated with PCB microelectronics assembly. It involves a combination of flip-chip and BGA (FCBGA) packaging, as shown in Figure 1. This is nothing new since this type of packaging has been around for the past 15 years. But now, it’s entering into a more prominent phase since FCBGA is of utmost importance in the microelectronics assembly and manufacturing of newer, smaller medical devices, as well as small mil-aero, commercial, and industrial devices.

zulki_0920_figure.jpg

Figure 1: A BGA and a flip-chip interposer. (Source: Thorsten Meyer, Wikipedia, with minor modifications in red)

But before going there, let’s take a step back to take another look at conventional BGA packaging to fully understand the importance of FCBGAs.

With conventional BGAs, I’m talking about traces and spaces in mils (one-tenth of an inch) rather than in microns. For example, 25 microns equals one mil. This means that if you are running a trace from two pads of a BGA on an FR-4 or any other organic substrate like Rogers, you need to have a BGA pad pitch of at least 30 mils on a 10-mil ball size to run a trace of three or more mils in between adjacent pads. That’s not possible from a real estate and size perspective when it comes to microelectronics simply due to the fact everything is so tiny.

This is where FCBGA comes in. This flip-chip assembly shrinks the conventional BGA down to one-third to one-fourth the original size and, at the same time, all the necessary connections can fit into that one-third or one-fourth of the physical size of the BGA. By doing so, more valuable space is created on an already small flex or rigid-flex circuit board. In other words, the same circuitry can be designed on a lot smaller real estate, when you go from BGA interposer to a flip-chip.

That’s only part of the story that an FCBGA brings to the PCB microelectronics assembly area. The other is more extensive and lands squarely on both the EMS supplier or contract manufacturer and the OEM. Both parties must have an understanding of new advances in the redistribution of layers (RDL). In the case of a flip-chip, in particular, RDL conveys signals from a die out to pins that solder it to the circuit board and through the BGA, effectively reducing the amount of real estate involved.

At the top of the RDL list, at the outset of a PCB microelectronics assembly project, EMS providers collaborate with their OEMs on the correct flip-chip material. Will organic or inorganic material be used for making the substrate to install BGA and flip-chip? And will chip connection C4 or C2 material be used for the flip-chip bumps? Regardless of which one is chosen, careful considerations must be applied because each has different characteristics and has a definite application.

In many instances, C4 bumps are used in area array flip-chip packages. However, it’s not suitable for ultrafine-fine flip-chip devices. The key reason is C4 solder bumps melt and collapse on the wide opening copper pads. On the other hand, C2 bumps are connected to copper substrate pads, which are a surface treated with organic solder preservative (OSP), with reflow and no-clean processes, ideally speaking.

Also, discussion and recommendation take into account wafer size, whether it’s six-, eight-, or 12-inch. Bumps have to be put on each chip, but typically on the wafer-level—not on the individual die-level—and the industry term for this process is under bump metallization (UBM). Six-inch wafers are less costly to process compared to eight- or 12-inch wafers.

Beyond these key points to be considered, there are a number of others:

  • Making the bumps either with C2, which is copper pillar, or C4, which are solder bumps
  • Solder paste to be used, such as SAC 305 or tin-silver, or another type, like tin-lead
  • Recommended BGA pad size on the die and the RDL substrate
  • Will the OEM provide bumps at the wafer-level or on the die-level?
  • What type of flatness is acceptable to the OEM customer when it comes to the RDL substrate as it pertains to attaching the die on a substrate like PCB?
  • What are the advantages and disadvantages of using an organic RDL substrate like FR-4 or Rogers versus inorganic material like gallium arsenide or alumina?

As indicated here, the introduction of FCBGA presents new questions and challenges for PCB microelectronics assembly. They are best resolved when OEMs get an early start with their EMS providers to discuss how to effectively approach the microelectronics assembly of new and smaller devices, whether they be medical, military, industrial, or commercial. The important thing to keep in mind is that you are creating a flip-chip from a BGA and still making the same connections. The result is utilizing only 30–40% of the circuit board space to perform all the connections.

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

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2020

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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07-08-2020

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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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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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Zulki’s PCB Nuggets: 7 Steps to Successful Assembly for Medical Devices Using Microelectronics

02-12-2020

Seven major steps need to be taken to achieve successful SMT and microelectronics assembly for medical electronic devices. Zulki Khan explains how these key steps take on special significance for newly emerging implantable and ingestible medical devices and result in medical devices that are robust, smaller, highly reliable, more powerful, and lighter.

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Zulki’s PCB Nuggets: Successful PCB Microelectronics Assembly

01-15-2020

In addition to coverage of PCB microelectronics subjects, Zulki Khan addresses one of the most crucial areas: PCB fabrication that creates the circuit board undergoing microelectronics assembly. The burning question is, “Why is fabrication vitally important when it comes to successful microelectronics assembly?”

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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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