A Guide to Design for Manufacturability

In manufacturing, engineers often use terms such as DFM and DFMA, which can sometimes be confusing. This article TechSparks aims to clarify the meaning and importance of DFM to help you better understand and apply it in the manufacturing process.

Table of Contents

What is Design for Manufacturing

You can find the DFM design for manufacturing definition on Wikipedia, and the screenshot below shows what it is. In this article TechSparks intends to express its concepts in plain language. It serves as a connection between design engineers and production operators, aiming to simplify, enhance, and optimize electronic design. The ultimate goal is to help companies produce high-quality products at a lower cost.

When your project is still in the design and development stage, it’s important to consider DFM manufacturability analysis. This ensures a close link between design and manufacturing, leading to successful product realization. Here are some questions to consider for DFM analysis:

  • Identifying and resolving potential design issues
  • Avoiding component layout errors
  • Exploring cost-effective alternatives
  • Enhancing production efficiency without compromising quality
  • Optimizing production lines to reduce costs
wiki design for manufacturing

Importance of Design for Manufacturability

For most companies, their primary objectives in production are clear: achieving low cost, high output, high quality, and ensuring long-term supply. Essentially, they aim to maximize profitability while minimizing expenses. These goals align closely with the essence of DFM, as DFM guidelines are crucial for improving efficiency, accelerating production speed, and enhancing product quality.

It is widely acknowledged that the cost of production is heavily influenced by product design, with approximately 70% of the total product cost attributed to the design phase. Factors such as the chosen materials and production processes greatly impact costs.

Influence of each product cycle
Influence of Each Product Cycle
Here are the significant implications of the DFM guidelines:
 
  • Reduce the overall production cost of the project;
  • Achieve fast turnaround and bring products to market in a short period of time;
  • Reduce new product development time and cost;
  • Reduce the number of design revisions;
  • Reduce rework rate;
  • Identify errors and failures before production begins;
  • Upgrade products to make higher quality products.
Application of DFM in each stage of product
Application of DFM in Each Stage of Product

What happens without Design for Manufacturing Analysis?

Lack of Better Options

Procurement of electronic internal components can be a headache. Often, the same electronic components can be obtained at different prices from various suppliers, directly impacting the overall cost of the printed circuit board. You may think that PCB DFM mainly competes for prototypes, and the quantity purchased is small, so you don’t have to worry too much about it. This is an unacceptable point of view. Neglecting attention to cost in small quantities can lead to significant cost increases once the prototype moves into mass production.

To illustrate this, let’s consider an example. If a component is used 10 times in a design and the price of a single component increases by 1 cent, the cost of a single board will increase by 10 cents. In batch projects, the order quantity is often 100,000 or even more. Therefore, the cost impact can be substantial. Furthermore, this example only accounts for a single component. Considering that a PCBA board may contain tens or hundreds of components, the additional cost can quickly accumulate.

Another critical concern is the supplier’s capacity to meet the demand. If a specific component is crucial for the PCBA, and it faces a shortage, it poses significant risks for the enterprise, especially during the final stages of production. In such cases, there may be a need to redesign the circuit board to accommodate alternative materials, resulting in potential delays and additional efforts for the design team.

dfm in PCBA

PCBA Failure

In PCBA, when considering DFM, it is important to also address DFMA (Design for Manufacturing and Assembly). Here are some common issues to be mindful of:

  • Poor solder joints: During the wave soldering process, component rotation is necessary, and any errors can result in subpar solder joints for both SMD and through-hole components. Proper component layout also plays a role in ensuring good solder coating. Placing components too close together may hinder the quality of solder coating on neighboring components.
  • Soldering short circuits: In the process of soldering SMD components, solder is applied to the pads, and the component pins are then positioned on the pads to form solder joints through melting. When the spacing between these components is too tight, it can create thin solder bridges between pins, leading to intermittent short circuits that are difficult to detect.
  • Tombstone effect: Uneven heating of a component’s leads during reflow can cause one of the pins to lift, resulting in the component standing upright like a tombstone.
  • Floating components: Non-compliant pad dimensions, which deviate from manufacturing design guidelines, can lead to misalignment and floating of components during reflow, potentially affecting other circuits.

These are just a few common issues. Failure to adhere to DFM and DFMA principles can result in unexpected problems during the actual PCBA process, requiring additional time and effort for desoldering, inspection, and reassembly.

Gold finger tin dip
Gold Finger Tin Dip

Reliability Design

Design reliability is frequently overlooked, with designers often prioritizing functional aspects over PCB assembly and practicality. However, it is crucial to consider factors such as temperature, humidity, and chemical corrosion when designing outdoor electronics. These considerations should be incorporated into the circuit design and material selection process. Additionally, relevant tests should be conducted after production to ensure that the design meets the requirements of the specific application.

Manual soldering components
Manual Soldering Components

How to Design for Manufacturing

Start with a Schematic

Before starting the schematic diagram, it is important to understand the application environment and functional requirements of the electronics in order to select suitable raw materials. During this process, factors such as price, supplier availability, and product life cycle should be added to the design for manufacturing checklist. Taking these factors into account from the beginning can prevent potential issues and avoid working with unsuitable manufacturers.

Furthermore, special attention should be given to the Bill of Materials (BOM). The market offers a wide range of compatible materials that can effectively address various needs. However, it is essential to consider the future availability and replacement options in case production needs to be discontinued. Taking proactive measures to anticipate potential challenges can save time and prevent complications in the long run.

Schematic Diagram

PCB Layout

PCB layout involves planning the arrangement of electronic components, wiring, pads, and other elements on a circuit board, which directly impacts the manufacturing process of the board.

  • Determining the number of layers

The choice of single, double, or multilayer depends on project complexity and requirements. Single-layer PCB is cost-effective but suitable for simpler projects. Two-layer PCB is often preferred for signal integrity and thermal management. Multilayer PCB is offer more design flexibility but come with higher costs and longer lead times. When considering DFM manufacturability, factors like required board thickness for vias and optimal drill aspect ratio need to be taken into account, which may require different board materials or adjusting the number of layers.

  • Defining the board outline

The model, shape, and size of the PCB should be determined based on project requirements, including the placement of fixed components, through holes, slots, etc. Careful consideration at this stage helps avoid redesign and assembly errors.

  • Selecting materials

To ensure smooth assembly and prevent soldering issues, it is crucial to have the necessary materials prepared in advance.

Place and Route per DFM Requirements

In high-speed and power circuits, it is crucial to ensure optimal electrical performance by keeping trace layouts as short as possible. However, it is equally important to consider the manufacturing requirements of the PCB board. To strike the right balance, TechSparks recommends incorporating the following points:

  • SMT: It is widely used in modern electronics, and it is essential to maintain proper component spacing during the design phase to facilitate automated SMT processes. It is advisable to refer to the manufacturing capabilities and guidelines provided by the manufacturer.
  • Wave Soldering: To achieve uniform distribution of solder around component pins, both surface mount and through-hole components should be oriented in a manner that allows them to pass through the solder wave during the wave soldering process.
  • Reflow Soldering: Smaller discrete SMD components require thermal balancing of their pins during the reflow soldering process.

Design Finalization and Documentation

  • Testing: To ensure the precision of the production process, it is necessary to conduct the required flying probe test on the circuit board after manufacturing. This test involves accessing the test points using probes in a test fixture. However, if the original design did not include the necessary test points, engineers would need to perform a costly redesign to add them. This not only incurs additional expenses but may also introduce new DFM issues that were not present before.
  • Silkscreen: It is critical for rework and debugging processes. If the board lacks proper silkscreen markings, it can slow down production, as rework and test technicians may struggle to locate specific components or polarity markings.
  • Design Summary Drawings: Complete and accurate information on design revisions is crucial. Without it, time may be wasted in verifying manufacturing details or, even worse, boards may fail during production.
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