Contract manufacturers play an important role in helping electronics companies get through Low-Rate Initial Production (LRIP) and eventually scale to high volume for new products. Contract manufacturers also help companies as part of NPI by producing PCB prototypes and PCBA prototypes. To ensure your product can be produced at or near target cost and with sufficient yield, some level of collaboration and communication with the contract manufacturer is essential. For companies without captive operations, they will have to communicate with the contract manufacturer on their own, or they will need to have their PCB design services firm determine the best approach.
In the PCB industry, we often refer to design for manufacturing rather than just DFM. For simpler designs that can be produced in high volume with minimal quality control measures, DFM and DFA practices are quite straightforward. For more advanced designs, such as those using HDI PCB manufacturing processes or advanced materials, successfully implementing DFM for a new PCB often requires deeper communication with a contract manufacturer. If you know what questions to ask early, you can avoid production delays and redesigns later.
Information You Need from Your PCB Contract Manufacturer
A PCB contract manufacturer has to provide a substantial amount of information about their process and the design constraints this imposes. This is bare-bones information for a standard PCB production process for simple boards or multi-layer boards. Process limits have to be converted into design constraints so that your PCB CAD system does not create features that are not manufacturable.
Process Limitations
Typically, a PCB contract manufacturer will give process capabilities information in table format, such as that shown below. They will typically provide a table with process limits for a standard or more advanced process, the latter of which carries higher cost. The table below is copied from one of our PCB contract manufacturer partners which we frequently use for client projects.
Table of process data from Sunstone Circuits.
With data presented in a table format, it’s quite simple to convert this information into PCB design rules in your CAD software. While it is true that 90% of constraint violations based on process limitations can be fixed easily, there is always the risk that a single constraint violation drives significant changes in the design. This should underscore why it’s so important to get this information early, as it saves design time, design cost, and delays before PCB manufacturing.
Standard PCB Stack-Up
Don’t assume that your preferred contract manufacturer or PCB supplier can provide the materials you specify. They may not stock the materials you specify in your stack-up, and the materials will need to be ordered, or the materials may not be available with reasonable lead time. Also, do not assume that a PCB manufacturer’s standard stack-up will meet an impedance spec in your design. Both assumptions can result in additional fees to design and qualify a controlled impedance stack-up, or to order specific materials for your design.
Depending on the level of advancement in your design, you might be able to use a standard PCB stack-up from the manufacturer. This will specify certain dielectrics and layer thicknesses that can be used in many designs.
Standard PCB stack-up example.
Looking up and using the standard stack-up from a PCB manufacturer eliminates any of the guesswork when designing a stack-up. You can also reach out to the manufacturer to inquire if they stock specific materials or equivalents.
Fabrication and Assembly Notes Review
Build requirements are specified in fabrication notes and assembly notes, which are then included in a master drawing. These drawing notes specify a range of requirements, most of which can be easily handled by most contract manufacturers. However, there are certain requirements one might specify in a fabrication drawing that should be checked against fabricator process capabilities:
- Surface finish, edge plating, and cancellation options
- Routing and drilling precision, particularly board cut-out or back drilling precision
- Misregistration precision, particularly in multiple lamination builds
- Warpage or planarity precision, particularly on HDI PCB designs
- Via fill and cap options and materials
Example PCB fabrication notes. Access these example fabrication notes at this link.
Once again, the material specifications in this list can influence reliability, and some manufacturers may not even offer the capability. In products targeting high-reliability areas like automotive and aerospace, reliability is always a major concern, and only certain materials will be qualified for use in these assemblies. It’s always best to ask first to ensure the fabrication capabilities will match your manufacturing needs.
PCB Assembly Capability
When component packages get very small, attrition rates tend to go up, and not all manufacturers can control defects. For this reason, some manufacturers will not offer assembly of certain types of components. In some cases, they offer assembly for smaller packages or fine-pitch parts only at a higher price, which then often carries a higher attrition requirement for components. In the worst case, the assembly is no-bid due to a lack of capability.
Some components where this applies include the highest-density SMD packages:
- 0201 and smaller case size parts
- Fine-pitch BGAs and micro BGAs
- Fine-pitch high pin count QFNs
- Similar bottom-terminated packages such as LGAs
Very small SMD passives.
Products with these components can see costs balloon, and yet certain products simply cannot be designed without these extremely small packages. Once again, it’s best to request information from your assembler and confirm they can handle assembly of these components with reasonable cost and attrition rates.
How Your PCB Design Services Firm Can Help
PCB design services providers have a responsibility to gather the relevant DFM requirements and manufacturing-driven constraints before starting a new design. It is not just about determining what type of PCB will be manufactured, it’s also about ensuring the design requirements align with capabilities, available materials, and performance criteria. The best PCB design firms have a comprehensive supply chain strategy with preferred manufacturers for client builds.
Whether you’re designing high-speed PCBs for mil-aero embedded systems or a complex RF product, you should work with a design and development firm that can ensure your product will be reliable and manufacturable at scale. NWES helps aerospace OEMs, defense primes, and private companies in multiple industries design modern PCBs and create cutting-edge embedded technology, including power systems for high reliability applications and precision control systems. We’ve also partnered directly with EDA companies and advanced ITAR-compliant PCB manufacturers, and we’ll make sure your design is fully manufacturable at scale. Contact NWES for a consultation.
