When I set out to buy my first car there was no shortage of advice from family and friends on how not to get stuck with a lemon. I cannot say how many times that I heard, “You get what you pay for.” Even being forewarned, I still managed to purchase a couple of cars that had more problems than I suspected. I can vividly recall lying in the snow on the side of the interstate trying to fix my car and get to an appointment for which I was already late. My Achilles’ heel when buying a car was always paying too much attention to its appearance and not enough to how mechanically sound or it was.
Failing to pay enough attention to the quality of construction of your boards can present a number of problems for your PCB development process. These can range from the inability of your boards to be manufactured to low yield rates or even premature failures in the field. However, there are ways in which these time-consuming and costly contingencies can be eased by design actions. Let’s first begin by answering your question, “What is the PCB fabrication process?” and then look at the importance of understanding the process for PCB development.
What is the PCB Fabrication Process?
It might not be helpful to jump directly into fabrication without knowing the relationships and steps between the schematic or idea you have in mind and getting that idea made. Before defining PCB fabrication, it may be helpful to define a few other terms and their interrelationships.
PCB Development: PCB development can be defined as the process of taking a circuit board design from the design to the production. This typically includes three stages: design, manufacturing and testing. And for all but the simplest designs, this process is iterative with the objective of arriving at the highest quality design within the development time allotted.
PCB Manufacturing: PCB manufacturing is the construction of your board design. This is a two-step process that begins with board fabrication and ends with printed circuit board assembly (PCBA).
PCB Testing: PCB testing, sometimes referred to as bring up, is the third stage of PCB development; performed after manufacturing. Testing during development is done to evaluate the board’s ability to perform its intended operational functionality. During this stage, any errors or areas where the design should be modified to improve performance are identified and another cycle is initiated to incorporate the design changes.
PCB Assembly: PCB assembly or PCBA is the second step or stage of PCB manufacturing in which the board components are mounted to the bare board through a soldering process.
PCB Development Stages
With that in mind, what is the PCB fabrication process?
The PCB Fabrication Process
PCB fabrication is the process or procedure that transforms a circuit board design into a physical structure based upon the specifications provided in the design package. This physical manifestation is achieved through the following actions or techniques:
Imaging desired layout on copper clad laminates
Etching or removing excess copper from inner layers to reveal traces and pads
Creating the PCB layer stackup by laminating (heating and pressing) board materials at high temperatures
Drilling holes for mounting holes, through hole pins and vias
Etching or removing excess copper from the surface layer(s) to reveal traces and pads
Plating pin holes and via holes
Adding protective coating to surface or solder masking
Silkscreen printing reference and polarity indicators, logos or other markings on the surface
Optionally, a finish may be added to copper areas of surface
Now, let’s see what this information means for PCB development.
Is it Important to Understand the PCB Fabrication Process?
The question can and probably should be asked: “Is it important to understand the PCB fabrication process?” After all, PCB fabrication is not a design activity, it is an outsourced activity that is performed by a contract manufacturer (CM). Although, it is true that fabrication is not a design task, it is done in strict adherence to the specifications that you provide to your CM.
In most cases, your CM is not privy to your design intent or performance objectives. Therefore, they would not be aware of whether you are making good choices for materials, layout, via locations and types, trace parameters or other board factors that set during fabrication and may impact your PCB’s manufacturability, production yield rate or performance after deployment, as listed below:
Manufacturability: The manufacturability of your boards depend on a number of design choices. These include ensuring that adequate clearances exist between surface elements and the board edge and the material selected has a sufficiently high coefficient of thermal expansion (CTE) to withstand PCBA, especially for no-lead soldering. Either of these could result in the inability of your board being built without redesign. Furthermore, if you decide to panelize your designs then that too will require forethought.
Yield rate: Your board can be successfully fabricated, while fabrication issues exist. For example, specifying parameters that stretch the tolerance boundaries of your CM’s equipment can result in higher than acceptable numbers of boards that are unusable.
Reliability: Depending upon your board’s intended usage it is classified according to IPC-6011. For rigid PCBs, there are three classification levels that set specific parameters that your board’s construction must meet to achieve a specified level of performance reliability. Having your board built to meet a lower classification than your application requires will likely result in inconsistent operation or premature board failure.
The examples listed above are not exhaustive but represent the types of problems you may experience if proper fabrication specification decisions are not made during design.
Understanding the PCB fabrication process is important
Therefore, the answer is an emphatic yes! It is important that you understand the PCB fabrication process as the design choices you make for this stage can reverberate throughout PCB development, production and even into operation. Your best defense against the types of problems that can result from not incorporating knowledge of the PCB fabrication process into your design decisions is the utilization of design for manufacturing (DFM) rules and guidelines that are based upon the capabilities of your CM.
In order to make the best use of DFM to guard against unnecessary time delays and additional manufacturing costs, you need to employ a comprehensive and capable PCB design analysis, such as Cadence provides. With packages, such as the Document Automation Tool, you can create multiple detailed views to aid your CM during the PCB fabrication process.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
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