It is absolutely mind-boggling that more people have a fear of dying in a plane accident than any other mode of transportation. In fact, you will be hard-pressed to find many people that are afraid of riding in a car. Yet, out of 100 transportation deaths, chances are that 95 (95.3%) of them will be by car, as compared to other modes of transportation, while only one (0.9%) will be during an airplane flight . Perhaps, at least partially because of this unfounded fear of flying, on the rare occasions when a plane does crash, it is studied until the root cause can be determined. Access to this essential information (due to the requirement that planes utilize flight recorders), coupled with an understanding of how planes are built, enables designers and manufacturers to make necessary safety improvements.
The same is true for building PCBAs. Knowledge of the manufacturing process is an essential asset that allows engineers and PCB designers to make decisions that will maximize board yields rates. The range of sizes and shapes that circuit boards may take is vast and application or installation environment-dependent. Even so, board construction can be divided into categories based upon the type and number of layers in the PCB stackup. Let’s take a look at the types of board construction and then delve into how multilayer PCBs are made, which offer the most design flexibility.
Types of PCB Construction
Today, circuit boards can be found almost everywhere. This includes the smallest electronic devices, most complex medical laboratory equipment, most sophisticated aerospace vehicles and virtually everywhere else. All of these boards fall into one of the construction type groups listed in the table below.
PCB CONSTRUCTION TYPE COMPARISON
|Lower manufacturing costs||Limited trace routing|
|Double-Sided||Increased surface area for mounting components||Longer time for PCBA|
|Multilayer||Smaller board size, more complex routing|
More complex fabrication
In the table above, single-sided indicates the board has traces and components on one side and double-sided indicates that the board has traces and components on both sides (top and bottom). As shown, single and double-sided boards do have advantages; such as simpler manufacturing and costs. However, the demand for smaller and more functional electronics requires that multilayer PCBAs where SMDs and higher stackup designs can be used for more complex internal layer routing. To fully leverage the advantages of the more compact multilayer boards is best done with an understanding of how they are built.
How Multilayer PCBs are Made and Why It’s Important to Know
The manufacturing steps for PCBAs are basically the same for all construction types with some important distinctions. These variances are related to the layup or multilayer stackup, which includes signal layers with etched copper traces, ground layers that are typically solid planes and insulation or dielectric between them. Specific issues for board fabrication and PCB assembly that are common for multilayer designs are as follows:
Multilayer PCB Construction Issues
- Layer alignment
Multilayer boards, in contrast to single and double-sided PCBAs that usually have two or more layers to align, may have stackups that include dozens of layers. For current flow through the board’s internal layers, plated through holes (PTHs) must be properly positioned which requires the board layers to be accurately aligned.
Delamination is when the copper laminate becomes detached. This can occur on the surface or on internal layers. Surface delamination can be fixed, if irreparable damage to the board does not occur. For multilayer boards, there are more potential areas where delamination can happen. In this case, the board will most likely need to respin.
- Moisture and contamination
Any type of contamination can be a problem for your board by interrupting operation or creating shorts that can damage the board, components, and traces. However, moisture is particularly dangerous due to the many ways it can be introduced on or within a multilayer circuit board. The best PCB moisture protection includes attacking this issue during manufacturing and packaging.
- Drilling precision
Typically, multiple layers are drilled simultaneously which means alignment is critical. However, the bottom layer of these stacks will usually have a larger deflection or the hole will be larger than for the internal layers. This can pose a problem as a larger annular ring diameter may be necessary for the larger deflection.
- Via selection
Another important issue when building multilayer boards is what is the best via option. Your choice of vias does impact your board build. For example, blind and buried vias require greater precision than through-holes. Component packages that have fine pitches and require via-in-pad vias can also be problematic for some contract manufacturers (CMs).
|Tempo‘s Custom PCB Manufacturing Service|
The list above includes issues that must be considered when your design calls for multilayer PCBAs. And your choice of CM may be the difference between high-quality boards manufactured quickly and an inefficient process that may not meet your capability needs. Tempo Automation is the PCB industry leader for prototyping and low-volume production of high-quality, complex PCBAs that will meet your requirements.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on how multilayer PCBs are made and what you need to know to ensure your boards meet your needs, contact us.
 These statistics are from published data by the National Transportation Safety Board (NTSB) for 2017. https://www.ntsb.gov/investigations/data/Pages/Data_Stats.aspx