Electronic circuit designers have to consider plenty of things designing a printed circuit board. It becomes critical to consider the type of PCB to design, but design components such as the components, separation of ground levels (if it incorporates a hybrid of digital and analog PCB), placement of components, among many other considerations. However, one key aspect that every designer needs to take into consideration entails pitch size. In this article, I will detail fine pitch PCB and its assembly process.
A Brief about Fine Pitch PCB
A fine pitch PCB implies printed circuit boards having a considerably high number of components for every square inch. Therefore, components prove close together with the board’s design guidelines pushing the fabrication limits of the printed circuit board fabrication. A fine pitch PCB also gets inferred as a high-density PCB.
Before we get into the design and assembly process, it becomes imperative to understand a few things about high pitch PCBs, especially regarding crucial components.
- Screw terminal 2.54 mm pitch. The screw terminal component is crucial and comes as a simple two-position screw terminal containing 2.54mm pitch pins. Such a pitch allows it to align with the typical 0.1-inch perf boards.
- 2.54 mm screw terminal blocks. It comes as a side-entry screw terminal block and contains a 2.54mm or 0.1-inch pitch. It can become an excellent alternative to the typical 0.1-inch female or male headers that most printed circuit boards feature. The reason this becomes possible entails the terminals proving capable of releasing and holding wires through adjustment of screws, which allows for temporary connections to the PCB.
- 2.54mm terminal blocks. The 2.54 terminal block is an important component in a PCB that helps keep loose wiring in check when making PCB-to-wire connections. The spacing allows them to fit perfectly into breadboards (solderless).
- Veroboard pitch. It implies a 2.54mm hole size drilled into the copper track rows that feature this PCB design.
It becomes crucial to understand what these terms imply as you will constantly encounter them in the fine pitch PCB assembly process.
How to Design a Fine Pitch PCB
Fine-pitch components always become a common feature for high-density applications and often drive up production capabilities and cost. If a component is smaller, the pads also become small, and thus, will necessitate the need for the place and pick machines to prove accurate. However, when deploying grid-array and leadless-based components, it becomes essential to carry out x-ray inspection when assembling.
As a designer, it becomes imperative to develop a closely-knit relationship with the PCB manufacturer/assembler to help you come up with a fine pitch PCB. It becomes essential because plenty of the details and decisions will depend on the facilities available on the assembly company. Your printed circuit supplier has to furnish you with broad guidance regarding risks, especially from CAM operators, among other technical representatives from board houses.
At RayMing PCB and Assembly, our support and engineering teams will guide you in ensuring that the realization of top-quality results becomes feasible, primarily in assembly and manufacturing. For any inquiries, please check our homepage and get in touch with us.
Designing often requires a layout, something that a designer must think through carefully before starting the design process. Otherwise, it becomes easy to get trapped into the numerous pitfalls that can render your design inefficient. So what are some of these potential pitfalls you can face?
Potential Fine Pitch Layout Problems and Important Steps to Avert Them
The layout process of hundreds of PCB components within a small limited space can prove daunting and complex. In most cases, it will require plenty of trial runs to avert pitfalls and issues. Below, some of the crucial pitfalls to avoid.
- Misplaced or unplaced components from the schematic
- Overpopulated the PCB without adequate room for trace design
- A lack of consideration for isolation and high-speed traces
- Lack of compactness
It, therefore, becomes essential to carry out the design process process-wise and below the process.
- Component selection. Firstly, it becomes pivotal to select small components to ensure they fit within the limited board space when placing. However, it can always become a careful balance between saving the board space and saving costs.
Remember, it always proves costlier to assemble finer pitch components, especially when they have to get populated. It becomes more arduous when the components need a particular inspection like the ground array, which relies on x-ray inspection.
The cost always shoots when tolerances become tighter, and you have to get your priorities right. For instance, if you want to save or cut costs, picking larger components might prove ill-advised. Most integrated circuits come complete as a package, and it could prove useful to consider the datasheet when populating your schematic.
Component ratings should also guide your selection of components. It represents another crucial aspect that needs consideration for every component. Additionally, a balance needs to get created and weigh the desired margin to build components like capacitors concerning package size.
- Board size. It comes as the subsequent step after the component selection in assembling the PCB. Here, you have to define a reasonable board size for starters. Additionally, based on the existing mechanical constraints, a dimensions limit might become important, especially on the Z, X, or Y due to the environmental variables. If, for instance, the board’s mechanical details are under development and the size proves negotiable, then the process becomes easier.
Characteristically, the size of the board will direct the needs of the mechanical hardware. You, therefore, have to specify and verify the size of the targeted board to the mechanical unit responsible for the assembly. However, it becomes crucial to check the potential usefulness of the small board. It can get accomplished by placing bulky components, outside connectors, and large integrated circuits that need extra surrounding room to break signals. All of these consider sensitive traces besides their isolation or separation from the other components of the board. It becomes easier to save costs by selecting pre-set board shapes/sizes like fitting plain square shapes with particular dimensions.
Important considerations to make at this point include clearances, trace width, and vias proportions. However, remember the importance of concessions, especially when it comes to costs. With the determination of the fine-pitch integrated circuits by this point, the requirements then get defined. Remember, the fine-pitch IC determines the design needs. For instance, a 0.4mm ball pitch BGA component needs the specs fulfillment of the same to function seamlessly. Whenever you want to use a high-speed integrated circuit that needs differential pairs besides impedance control, a vendor has to get reviewed. For instance, a connector may require diverse odd-shaped slots and may subsequently under the custom capability.
- Component placement. At this point, the placement of component start and includes fitting them close together but with sufficient room vias, traces, planes, etc., and proves more of a trial process until completed.
Firstly, placement starts with high-speed and high-power components besides connectors and extra mechanical components. Once placed, you get an established framework to start working from. Considerations when it comes to fine pitch design optimization of the board space, you have to consider the following.
- Via-in-pads. It comes as a non-recommendation from assembly houses, though one can free up some space between tightly-spaced components for the traces. It especially entails establishing vias on component pads, and these come as capacitors, resistors, ICs, etc., to conserve the routing room. Nonetheless, a risk exists that components may not receive enough solder connection due to the surface area the “via” consumes.
- Decoupling capacitors. It mostly gets placed on top, near, or below sensitive pins. Placement becomes critical on the PCB. However, these decoupling capacitors might end up occupying plenty of routing/board space. It sometimes happens that some of the capacitors get left out, and this adds the risk of noise on sensitive digital/analog signals. However, the risk may prove minimal.
- Fiducial marks. Incorporating these image system’s guide markers allow the machine (pick and place) to identify the location of the printed circuit board. A 1mm diameter circle atop the copper layer (devoid of solder mask) is commonly incorporated at the PCB’s corners. While not necessarily required for the printed circuit board assembly, it helps with the placement precision when the vendor assembles.
- Tooling holes. It represents a crucial and useful addition to the testing and assembly process of PCBs. It helps align drilling holes, solder stencils, text fixtures, and pick and place equipment. Tooling holes can become instrumental for board mounting into an enclosure.
- Special modifications. Reducing the volume that odd-shaped and bulky components occupy makes it important to trim off a component’s segment by trimming. Such segments may entail needless metallic shields and component protrusions.
- 3D parts. It becomes possible to import comprehensive connector and extra mechanical-based part’s step files to allow for precision planning and placement. It allows for the depreciation of clearance between the board edge and the parts pads.
- Test points. It also becomes critical to remember the capacity of testing every signal that gets related to the fine-pitch components.
Final thoughts
It always becomes pivotal to balance the complexity and cost aspects regarding printed circuit board assembly and fabrication besides understanding that the concessions can save you time and money during the product’s production and development. Hopefully, this piece has answered some pertinent fine pitch PCB assembly issues you might have had. However, in case of further inquiries, go to our homepage and get lodge your questions.
