PCB DFM Guidelines – Design for Manufacturing
DFM comes from the acronym of the word “Design For Manufacturing”, and can also be replaced by DFMA (Design for Manufacturing and Assembly), it means to make a design thinking about facilitating the processes in the manufacturing stage of a device.
The main purpose of PCB DFM is to facilitate the manufacture of products in the best possible way and at the lowest cost, this will include a number of considerations such as:
- Search for a simplified PCB assembly, which is easy and simple to design and manufacture;
- Make a selection of appropriate materials that do the job well but are not the most expensive;
- Use shapes and designs that optimize the use of raw materials and refine the product in such a way that it still retains its aesthetic details.
Five stages of DFM in PCB
There are five DFM processes to keep in mind when working on a PCB or PCBA project, these phases are:
- Cycle of use: This is how people will use the product and also includes the PCB assembly process, what steps will be required, what tools will be needed and how the assembly will be completed as quickly and easily as possible.
- Design: This includes design of the electronic circuit, PCB design, location of the connectors, suitability of the position of the connectors and feedback with the Industrial designer to know where to place the indicators, control buttons, connectors and cables going to and from the printed circuit board.
- Material: Here you define if the material requires special conditions such as heavier weight copper (commonly 1oz or 2oz) or thicknesses for the PCB substrate material (e.g. FR4 or aluminum) or its thickness as there are PCBs with thicknesses from 0.4mm to 2mm (they are not the only ones) depending on the application e.g. some RF designs will require PCBs to have smaller thicknesses.
- Environmental: Environmental requirements may include roHS certifications, lead free PCB assembly certifications, electromagnetic emission limitation and electromagnetic interference resistance certifications such as FCC, as well as other special certifications applicable to the use of the device depending on its environment of use.
- Compliance/Testing and calibration: The set of tests or analyses to which the printed circuit board will be subjected before assembly must also be defined. This is especially important if the printed circuit board is large, contains many components or is so costly to manufacture that the tests will ensure that no defective elements will be overlooked from an electronic point of view. These tests can also be associated with laboratory PCB tests aimed at obtaining any of the certifications already described.
The process should occur in the early stages of design even long before the creation of sketches begins, it can be said that PCB design for manufacturing should start together with the idea of the device to be designed understanding above all, how it is going to be used by the customer.
In order to work and be effective, it must include all parties involved in the design for manufacturability process: electronic engineers, PCB designers, industrial designers, PCB manufacturers, mold makers and material suppliers. The DFM must be “cross-functional,” it is important to be able to have a broad and clear view of the design process at all levels: components, functional blocks, systems and assembly, to ensure that the design is conceived in such a way that it does not have unnecessary costs.
An early PCB DFM rule reduces the cost of requested changes during the design process. As the design progresses in time through the product design cycle, changes become more costly and more difficult to implement (It is this difficulty that makes such changes costly). A well-planned and executed DFM allows design changes to be executed quickly, in the least costly location.
Bringing together the stakeholders in your product development process early in the design process is easier if you are developing a new product, but even if you are thinking of developing a second version for a product that already exists in the market, a full PCB design for manufacturing checklist is necessary. Too often, mistakes in a design are repeated again when replicating a previous design. Question and critique every aspect of your design during this DFM process.
When starting a DFM process try to find out what problems you might face, make a design sequence, list the problems you might face at each stage and then look for similar products, analyze how you have solved these problems and try to implement this solution yourself.
It may help to talk to your electronic designer or your PCB designer and ask how they have solved similar problems on previous designs.
You can also contact the manufacturer, both the printed circuit board manufacturer and the enclosure supplier, or consult with your industrial designer.
Always ask yourself, is there a way to do it better?
You better spend a lot of time, dedication and sacrifice in developing a good DFM process, it will pay off in the subsequent PCB design and PCB manufacturing process.
PCB DFM Checklist
- Cycle of ues “Process”
If you are building prototypes, there is no need to wear aerospace category requirement materials or PCB fabrication with high environmental certifications; nor should you require fabrication of very complex board shapes if you are only going to build small quantities. Unless the design requires it, because it means the construction of tools and dies for manufacturing small volume parts, and will increase the cost of PCB prototyping.
It must take into account the quantity of parts to be manufactured, the material to be used, the finishes, the tolerances required and whether secondary processes are required.
The design is the backbone of the product ideation process, here you must take into account all the conditions that must be met. PCBA components should not be oversized in either dimensions or electronics capability. However, proper component selection should follow electronic design standards by selecting those components that can withstand at least twice the capacity over which they will be used.
Tracks should be of adequate size for the amount of current they will have to carry. Signal tracks should be small enough so that they do not take up unnecessary space. Dimensional tolerances should be defined.
Boards that will require automated assembly by pick and place machines should have fiduciary added to them in order to speed up the manufacturing process.
You should also talk to your manufacturer to define if tooling holes are required. Be sure to discuss the design with your contract manufacturer, who can ensure that your design conforms to good manufacturing principles for PCBA fabrication.
It is important to select the right material for your printed circuit board. DFM Requires you to review some aspects of the material to be used such as:
Mechanical properties: How strong should the material be?
Color: should the welding mask have a specific color? The silkscreen should generally contrast with the mask.
Thermal properties: How heat-resistant should it be?
Electrical properties: Does the Board conduct large amounts of current? Will there be large amounts of voltage? The thickness of the tracks must be taken into account for current calculations and the gap spacing for voltage calculations.
Flammability: How flame resistant should the material be?
What is the required thickness? What is the type of substrate material to be used? Is it better to use FR4 or does it need to dissipate heat? So it is better to use aluminum.
Again, be sure to discuss the material with your PCB manufacturer, what compatible materials they have in inventory, which would allow you to secure a lower material
Your product must be designed to withstand the environment to which it will be exposed.
Will the Board be used in a hostile environment? Vibration? Will it be subjected to high temperatures? Will it be exposed to the sun’s rays? Can it work in environments with high humidity content? Will it be designed to work in flammable atmospheres?
- Compliance testing
Except for some prototypes produced in low quantities, all products must meet safety and quality standards. Sometimes these are IPC PCB standards, sometimes they are regional standards, and sometimes they are internal standards specific to the company or to you as a customer.
Do you need any ISO certification?, who will provide UL testing, ETL etc.? Who will perform and where will such testing be performed?
Factors Affecting Design for Manufacturing
PCBA DFM’s goal is to reduce manufacturing costs without reducing performance. In addition to the points mentioned above, there are also other elements that can affect its design and assembly.
- Reduce total number of parts to be used
This is the easiest way to reduce PCBA manufacturing costs because we will use less material, the intervention of engineers will be less, the production processes will be shorter, the labor force will be lower and even the weight could be reducing shipping cost.
- Unify the use of the shapes of the parts and materials
Making custom parts requires time and money. It is better to standardize the dimensions and shapes of PCB boards that you could use in different devices or make designs that can perform different functions according to the components that are installed on them, a single board that can perform several functions.
- Use modular assemblies
If you base your manufacturing on commercial modules and non-customized designs; you will be able to modify the product smoothly at a lower cost.
- Design for easy connection of your PCBs
It is always better if you can make a design where you do not need a large number of PCB connectors as these will increase the price, however, if so, you should use commercial connectors.
- Keep quantity and size to a minimum;
- Use standard connectors as much as possible;
- Use self-tapping screws for faster and better placement;
- Avoid screws that are too long or too thick, split washers, threaded holes, special heads and heads that require special tools.
- Minimize reorientation of parts during assembly.
PCBs should be designed to require minimal manual interaction during assembly.
- Decrease the number of steps required during your manufacturing process
The more steps your product development process includes, the more likely it is that an error will occur. As long as processes are kept simple, errors are reduced. Only include those processes that are essential to the manufacture of your device.
- Define acceptable
Focus initially on your Board being able to perform the functions it is supposed to perform then you can worry about show grade finishes.
FS Technology hope that these tips about design for manufacturing can help you to obtain a good quality PCB aimed at reducing final assembly costs.