With COVID-19 continuing to rage across the United States and the world, hospitals and medical centers are relying on their medical electronics equipment, including ventilators, to help improve COVID-19 patients’ health. EMS providers, contract manufacturers (CMs), and printed circuit board (PCB) fabricators are the strongest link in the supply chain critical for building medical electronics equipment, including ventilators. These PCB companies help design, assemble, and manufacture the PCBs that are at the heart of these life-saving medical instruments.
At this time of urgency, medical electronics OEMs must keep in mind the basic, yet critical requirements demanded by all medical electronics products: quality, repeatability, and reliability. This trio of requirements must be completely and conscientiously exercised at layout, fabrication, and assembly.
The ISO 13485 standard and U.S. Federal Food & Drug Administration (FDA) regulations fully support those three requirements. As defined, an EMS provider or CM that has ISO 13485 certification holds the “proof of Quality Management System compliance to the standard involved in the Medical Device industry.” Similarly, the tightly controlled FDA approval process requires precise documentation, audits, design capability evaluation, and verification, including clinical trials. For example, this means that when information for a ventilator PCB design is not properly documented, there are flaws in clinical studies, or the design is incorrect or incomplete, then adverse effects arise during PCB assembly, leading to challenges in obtaining FDA approval of the finished device.
With that backdrop, medical ventilators and other medical equipment cannot afford failures whether it’s in the lab or in the field. The burden is on the EMS provider to ensure that PCBs are designed to be extremely reliable and that they deliver quality time after time.
This means that the EMS or CM must have well-disciplined quality measures throughout the assembly and manufacturing process, such as automated optical inspection (AOI). Figure 1 shows an AOI system verifying every component on a PCB and then “passing” the board. Other quality control (QC) steps include first article inspection (FAI), x-ray, and multiple sets of QC checks along the way.
Therefore, maintaining high-quality manufacturing translates directly into high reliability. The EMS provider or CM must always be checking, evaluating, tweaking, and streamlining that process to make it as strong as possible. With such a stringent manufacturing process, quality and reliability come at a price: an EMS provider must diligently pursue each and every step to ensure that it is attaining quality and the resulting reliability. Here, a highly experienced reliability manager on the assembly floor is a valuable asset to make sure there are no shortcuts, cutting corners, or shortchanging each quality step.
These QC steps are all embedded in the process. If manufacturing is run based on a set of disciplined and verified processes, the end result is a ventilator or other medical electronics product that embodies the highest level of quality.
The Role of Experience
Experience is at the crux of manufacturing medical electronics such as ventilators. But along with experience is the need for a continually growing knowledge about electronics engineering. For example, achieving Certified Interconnect Designer (CID) or CID+ certification plays a major part in successfully addressing the complexity of PCB layout, routing, high-speed terminations, impedance control issues, and other related design points.
It’s important to understand device packaging dynamics. Advanced medical electronics products like today’s conventional and portable ventilators rely on such state-of-the-art device packaging as package-on-package (PoP), flip chip, land grid arrays (LGAs), and tiny passive device packages such as 0201 and 01005 packages.
There are also a number of so-called quality gates that a PCB assembly house has to pass through to maintain ultra-reliability. These gates include complying with the ISO 13485 quality standard. The ISO 13485 medical electronics standard is the equivalent of Mil/Aero J standard for manufacturing. Both demand tight tolerance controls. Medical electronics PCBs have similar, and in some cases, stricter requirements than those used in mil/aero products.
At PCB Assembly
The thermal profile and stencil design and associated solder paste are two prime examples of processes that are critical to maintaining quality and reliability during PCB assembly. In simple terms, a thermal profile is a recipe for preparing a surface-mount (SM) component-populated PCB for the infrared (IR) reflow oven. A particular profile must be correctly designed and implemented for a given medical electronics PCB.
The thermal profile records temperatures under different components on the PCB surface to create a custom thermal profile, which includes three different area segments: soak, peak temperature, and cool-off period. As shown in Figure 2, zones 3, 4 and 5 are soak periods; zones 6, 7, and 8 are peak temperatures; and zones 9 and 10 are cool-off periods.
It is important to note that if the thermal profile is not correct, and the board is not profiled properly, the result will be cold soldered balls on the ball-grid array (BGA), chip-scale package (CSP), and/or quad flat no-lead (QFN) devices. If the thermal profile is too hot, bridging results (see Figure 3). Therefore, if a thermal profile for a given PCB isn’t correctly designed, it will either be severely damaged during reflow, or it will incur latent flaws that could cause catastrophic failures at a hospital or healthcare center.
Properly defining a stencil design and associated solder paste dispensing are further examples of the steps critical for maintaining quality and reliability. Using the right paste, correct stencil design, and correct profile eliminates about 75 percent of potential rework and touch-up issues.
Eliminating PCB Defects
Multiple factors must be taken into account to eliminate PCB defects. A comprehensive assembly drawing detailing all necessary assembly processes is a critical first step. For example, process documentation can specify that all components, including BGAs, are to be machine placed, and this documentation can define any rework or engineering change order (ECO) callouts and the use of any special processes. Figure 4 shows an example of a properly created assembly drawing, which can eliminate confusion, answer questions, and reduce board defects.
Assembly processes must also be reliable for repeatability. In this instance, the first article inspection (FAI) is important at the assembly level so that technicians can check for polarities, missing components, and other key issues.
As shown in Figure 5, the system helps to create the first article board by scanning the image of the whole board, called a golden board, and then comparing the images of all the other boards with this golden board to ensure that all the components are placed properly on the board with correct orientation and polarities. It is used as a process verification and inspection tool to significantly reduce the human interface and make the inspection and QC process more reliable, repeatable, and faster by at least 30–50 percent.
During first article pre-reflow inspection — when boards are about to go for reflow — the process can be stopped. It can be changed, however, and a single board or set of two boards as second articles can be run to correct the process. If defects are not caught during the process, they turn up at the end of the process when it can be too late to address them. A shipment could be missed, or rework may be too involved, thus adding time, resources, and extra cost. Planning must also be conducted to determine and document:
Processes that need to be defined.
Use of special equipment (e.g., an arbor press for press fit connectors).
Use of an AOI machine or flying probe tester.
Documentation is also important for technicians in the field who need to read and decipher ECO instructions, which deviate from original build. Likewise, rework instructions, if any, need to clearly state solid quantitative data for measurement and verification purposes, including illustrations, if possible.
At times, instructions can be issued in an assembly drawing to avoid board defects, which could be process-related issues. Also, depending on how progressive an EMS provider is, post reflow x-ray inspection can be specified as part of the process for all BGAs, CSPs, and QFN devices, rather than performing these steps as part of the QC stage of the assembly process. Early intervention enables corrective actions to be taken to prevent board defects such as improper board reflow, poor orientation, wrong thermal profile, and improper flux activation, among other issues.
Lastly, it is essential that an EMS provider or CM always maintains a constant review of its assembly processes and procedures. This ensures that assembly is sustained at the highest levels possible to efficiently produce quality PCBs for ventilators or other medical electronics. Repeatable processes also minimize defects and issues at the QC stage and in the marketplace.