Exploring Methods for Rapid PCB Prototyping

At Rush PCB Inc., we are always under pressure to help our customers bring their new products faster to market. Rapid prototyping allows designers and engineers to test their concepts faster, iterate their boards quicker, and validate their designs more quickly before they start investing in full-scale production. We use several methods, techniques, and strategies to enable rapid PCB prototyping.

Advantages of Rapid Prototyping

There are several advantages of rapid prototyping. These include:

Time-to-Market is Faster — When engineers and designers get their working prototypes faster, they can finalize and launch their products sooner. This enables them to gain a better competitive edge.

Faster Design Validation — Testing prototypes early on informs the design and engineering teams about any potential areas for optimization or design flaws that must be corrected. This way, they can avoid re-spins later, when it may be more expensive.

Faster Iterations — Rapid prototyping helps designers achieve faster iterations, resulting in a better fit for the product in the market. They can refine their design with more iterations.

Cost Reductions — Rapid prototyping reduces development expenses while avoiding potential delays.

Faster Response to Changing Requirements — It is possible to address new technical challenges and changing customer needs with greater agility.

Fast Prototyping Techniques

Designers and engineers use some key techniques for rapid PCB prototyping. Some techniques they use include:

1. Prototype-Specific Design Rules:

To speed up their prototypes, designers often relax design rules, thereby enabling faster layout processes and manufacturing. This includes using:

• Larger trace widths and spacing
• Larger via sizes with higher spacing
• Relaxed impedance mismatches
• Single- or double-sided PCBs, without solder mask and legend printing

While the above relaxation in rules allows optimizing the speed, they do not offer long-term reliability or board size reduction.

2. Simplifying the Design

Designers also resort to simplifying their schematics and board layout by removing unnecessary complexity and components. This includes

• Small SMD packages like 01005 or 0201 only when essential

• Avoiding complex packages like QFPs, BGAs, DFNs, etc.

• Minimizing the layer count to about two by removing ground and power planes

• Using low voltage clearance rules like 50V, unless the circuit uses higher voltages

• Eliminating advanced interfaces of the type DDR, if possible

The above can help reduce the effort required in PCB layout and fabrication times.

3. Reusing Designs

Reusing existing schematic and PCB layout designs, symbols, and footprints can help accelerate prototyping. With design reuse, designers can avoid redrawing schematic capture and repeating layouts that consume time.

4. Prioritizing Functional Validation

Designers accelerate prototyping by focusing on validating only the core product functionality when testing the prototype for proof of concept. They relegate reliability testing, compliance, and other in-depth testing for later.

5. Building Multiple Revisions

Complex products can require several prototype revisions, and designers often plan for parallel prototypes to reduce the overall time.

6. Prototyping with Simulated Components

If real parts are not readily available, designers often use model boards, dummy components, or simulating other elements during prototyping before completing all dependencies. Of course, simulating electronic components may have limited feasibility.

7. Performing Regression Testing

To reduce prototyping time, designers often prepare automated test suites and scripts. This helps them validate key functionalities every time they build a new revision of the prototype. This helps them to detect any regressions easily.

Development Cycle for Rapid PCB Prototyping

Apart from relaxing a few rules and simplifying the design, a major part of the development cycle is the same for prototyping and regular development. Typically, in serial order, these involve:

1. Conceptualizing the design goals and the system architecture

2. Creating block diagrams and initial schematics

3. Making BOM, selecting components, and footprints

4. Laying out the initial PCB

5. Fabricating the first prototype

6. Assembling the prototype and developing a basic test setup

7. Functionally testing critical circuits and features

8. Analyzing results, improving the design, updating schematics

9. Rapidly iterating layout, fabrication, assembly, BOM, and test procedures

10. Repeating until design validation and achieving all criteria

The above cyclic approach enables engineers and designers to converge on an optimal design much faster than is possible through traditional linear development methods.

Fabrication Methods for Rapid Prototyping

Constructing the physical embodiment of the design happens during the build stage of development. Designers build or fabricate a new board during each iteration of the prototype cycle. They test each new prototype board, or a set of prototype boards, to validate the functionality and operation.

Typically, the fabrication processes yield a bare PCB, to which there are no components attached, although the designer has laid out the footprints and corresponding pads on the board. Subsequently, they connect the components to the board using through-hole soldering, surface mount soldering, or a combination of the two. This yields the final PCBA ready for testing. Depending on the complexity of the board and the capabilities of the CM, the process can be time-consuming.

New methods for rapid prototyping can improve the overall speed of fabricating the board. One of these methods is additive manufacturing or 3-D printing. These new fabrication processes are capable of building prototypes within a day.

1. Additive Manufacturing

Additive manufacturing, often used synonymously with 3-D printing, is the process of fabricating objects by adding successive layers of material. This method offers engineers and designers the convenience of fabricating a single or a few PCB prototypes very easily. Some types of additive manufacturing methods are:

1. FDM or Fused Deposition Modeling:

As implied by the name, the FDM or Fused Deposition Modeling method creates objects by stacking various layers and fusing them. The method uses various thermoplastics for the layers and fuses them through a heating and cooling process. Typical FDM materials are:

• ABS or Acrylonitrile Butadiene Styrene
• PET or Polyethylene Terephthalate
• PETG or Polyethylene Terephthalate Glycol
• TPU or Thermoplastic Polyurethane

For creating PCB prototypes, the designer combines FDM with LDW or Laser Direct Write, SLA or Stereolithography, and other processes. These add conductive materials and embedded components.

2. SLS or Selective Laser Sintering

As a power bed fusion technique, the SLS or Selective Laser Sintering technique uses a laser to make polyamide or nylon parts. The process uses a powdery substance to start, which the operator then heats to form various shapes.

3. SFF or Solid Freeform Fabrication Method

Rapid prototyping techniques often have the advantage of requiring minimum equipment for fabrication. Typically, the SFF or Solid Freeform Fabrication method uses a single machine—a 3-D printer—and nothing else, not even for tooling. Other than creating the initial computer model, the process requires no human intervention for the final product.

2. Additive-Subtractive Fabrication Method

The conventional method of PCB fabrication is the subtractive method, where the operator removes unwanted material from a larger solid block. Additive manufacturing is the opposite method that builds the final shape by adding layers of material. Some manufacturing methods use both additive and subtractive methods together for fabricating PCB prototypes.

1. LOM or Laminated Object Manufacturing

The LOM or Laminated Object Manufacturing is another rapid prototyping technique similar to other methods already discussed above. The process uses a bottom-up method that adds successive layers. The operator typically glues the layers together, and these may be made of plastic, paper, or even metal. They form the final product by cutting away the excess material with a knife or laser tool.

Although there are many processes and techniques available for rapid prototyping, LOM is the most popular. The fabricator creates the PCB stack up by adding successive layers, using an adhesive to secure them. This is the additive process in the fabrication. There are several conductor layers, which the fabricator must etch away to create the necessary circuit. The removal of copper and drilling of holes for vias and other holes is the subtractive process in the fabrication.

3. Additional Rapid PCB Prototyping Considerations

Whatever the fabrication process, the final output is a bard board without components. Subsequently, engineers must attach or assemble the components on the board to complete the prototype.

A new additive fabrication technology is available that allows the embedding of certain types of components during the fabrication. While this is still not a widespread method, it is gradually becoming more popular. However, these new techniques for PCB prototyping and fabrication typically require the use of proper design tools for the best outcomes.

Conclusion

Although there are many options available for rapid PCB prototyping and fabrication, we at Rush PCB Inc. have discussed only the most popular ones. Being aware of the options available and the tools necessary to rapidly make PCB prototypes allows the designers and engineers to make intelligent choices according to the resources available to them.