Archive for May, 2016

Risk Factors for Flexible Printed Circuit Boards

Written by Admin on . Posted in PCB

flex pcb

When PCBs are designed, the intention is to ensure they are robust and able to function effectively over the long term. However, PCBs can be damaged, and engineers need to be aware, and set risk management plans in place to avoid the risk of damage to PCB.

There are two factors that can lead to damaged PCBs. These are environmental factors, and problems that can develop during the design and production stages of flexible PCB manufacture. There are several environmental factors that can damage PCBs.

Moisture and humidity

In either form, moisture or humidity (which may condense to form moisture) can render a PCB non-functional. While an entire final product (e.g. a cell phone or television) may be able to survive a little amount of moisture, the individual PCB within these units will short out in the presence of moisture if the water crosses two channels on the PCB. While the active presence of moisture will cause this problem, similar issues may arise if the PCB is operating in damp conditions. In such circumstances, mold may form and lead to circuit failure.

Static Electricity

Small charges from static electricity can reach the boards in a variety of situations. If a static charge affects the board while it is in use, the risk is increased. PCBs need to be positioned in a location that is free from any source of static charge such as fabric or carpet.

Fumes

Liquid chemicals such as cleaning solutions may give off fumes. If the PCB is operating in close proximity to the fumes, they can build up on the unit and slowly corrode the linkages.

Temperature Extremes

Both cold and heat can have negative effects on PCBs. As noted under ‘moisture’, dampness can lead to boards shorting. Humidity is a relative entity. At higher temperatures, the air can hold more moisture than it can at cold temperatures. If the environment where the PCB is operating cools to the point that the air can’t hold the moisture, condensation will occur and as a result, shorting may also occur.  Heat is as much of an issue as cold. Heat can lead to the board warping, which may break the linkages and cause the PCB to malfunction.

Dust

Dust is present in most environments, and can cause two issues for PCBs. The first concern is that the dust may insulate the board, reducing the ability for heat from the board to dissipate. Dust can damage devices such as computers and televisions. The second way that some dust can cause damage is that it can be a medium for static charge.

Manufacturing Errors can also damage PCBs.

Every PCB design is different. By nature, each design has to be different, as they are all designed to meet different needs. While engineers will follow regular guidelines in designing their boards, and test the boards at various stages to ensure functionality, there is a risk of human error.

In addition to the risk of human error, there are inevitable risks in manufacturing. The manufacture of boards is complex, and there are several opportunities for defects to be included in the manufacturing process.  An example could be if two metal traces aren’t appropriately insulated, a high voltage may lead to arcing which will destroy the circuit.

PCBs – High Quality Design

Written by Admin on . Posted in PCB Design

pcb manufacture board

 

 

Almost every electronic item around you consists of one or more Printed Circuit Boards (PCBs). PCBs hold components and also provide connections between these components.

So, if you’re an Electrical or Electronics engineer, the chances are that you will design PCBs at some stage in your career. Despite this design being a key function of electrical engineering, it’s not something that is widely taught in engineering programs. It’s not difficult for engineers to understand the core functions required for effective PCB design. There are a lot of elements to consider. All functional requirements must be met including schematic designs, component placement, and routing. Other factors that need to be considered include the schedule and cost.

Create a Schematic Diagram

Converting the concept of requirements into a PCB will require electronic language and logic. Start with a schematic diagram. The schematic diagram will include the overall design and the interconnections between circuits and components, identify the component placement, and address other factors such as the PCB material and temperature requirements.

Generate a Bill of Materials

The Bill of Materials (BOM) should be generated in conjunction with the schematic diagram. It is a summary of all the components and links required for production of the PCB. There are five key aspects of the BOM:

  1. The number and type of each component.
  2. The identification of a component in a circuit on a PCB.
  3. The numeric value of ohms, farads, etc.
  4. The footprint of each component on the PCB, and if available
  5. The manufacturer’s part number.

Placement on the PCB

Each component will need to be located based on function, thermal management and electronic noise. The order of placement is:

  1. Connectors,
  2. Power circuits,
  3. Sensitive and precision circuits,
  4. Critical circuit components,
  5. Everything else.

Following the initial placement, the PCB should be tested and reviewed, with adjustments made based on power tolerance and budget.

Routing

All PCB components are interconnected through routed traces. Elements that should be considered in routing include power levels, noise sensitivity (or generation) and routing capability. As a guide, traces with a width of 10 to 20mils can carry the current of 10 to 20mA and 5 to 8mils of carrying current lower than 10mA. If there is a requirement for high-frequency or rapidly changing signals, designers should consider routing using high-frequency nodes.

Thermal Management

Heat is a crucial factor in design. An ideal design will keep the entire board at a uniform temperature during operation. Thecomponents and links with different thermal activity need to be balanced in the design. Factors to consider include copper thickness, the number of layers and the board size.

Three ways of addressing heat include ensuring solid ground or power planes with more layers that are connected directly to heat sources; ensuring the heat transfer is optimized by developing effective heat and high-current routes; and by maximizing the area used for heat transfer.

Completing a Final Check

A final check of the design will include Design Rule Checking (DRC). DRC will determine whether the physical layout of the PCB meets Design Rules (a series of recommended parameters). This is a major step during signoff on the design, and includes validating Layout Versus Schematic (LVS), XOR, Electrical Rule Checks (ERC) and Antenna Checks.

Electronics Design Tips

Written by Admin on . Posted in PCB Design

electric board

CAD programs provide a very effective tool for designing PCBs. Even with an effective program. A wide range of ideas/tips help you design your board efficiently.

Use Block Diagrams

A block diagram is a diagram of the overall system of your board where the main parts or functions are shown as blocks. Lines are used to connect the blocks to the relationships of the blocks. If you create a schematic drawing, you’ve only covered one part of your basic design. The schematic drawing should be able to be read by most electrical engineers.  A block diagram doesn’t go into as much detail as the schematic – it isn’t intended to show every connection on your PCB. Adding a block diagram will not add a lot of time in your designing process. However, it will add clarity to anyone trying to understand and use your design. A good block diagram will provide overall reference points for all the components in your board.

Track your Activity

Always make notes about what you’re doing. Don’t presume that you will recall why you structured a board in a particular manner. Whatever you happen to be thinking about when you configure a board in a certain way may not come back to you when you’re reviewing or revising. And if you have other team members you’re working with, they will need to understand your rationale as well.  So make detailed notes about everything; and keep the notes in a safe place. Don’t forget to include logic table settings, or configurations of power supplies. These are vital parts of your board structure.

Name Your Nets

If you’re designing a board, you will probably be aware of the details of each of the components, why you’ve used them in their locations, and how the board works as a whole. This overall awareness is great. However, at some stage you’re likely to need to review and possibly reconfigure what you’ve done. To achieve this, you will need to be able to recall how you designed each part of the board, and why you chose that configuration. If you name your nets, you (and anyone else involved in de-bugging your board) will be able to identify where functions are occurring and why you elected those locations in your board for the various functions. This will make validation a simulation runs a lot more simple.

Don’t Shortcut your Schematics

When you’re creating a board, make the flow obvious for yourself and for all readers. Don’t risk taking shortcuts on your schematics, even if your design takes many pages. There’s a risk that if you try to condense your plans, they may become hard to follow, and therefore hard to validate or re-create.

Use Clearly Visible Connectors

It may be stating the obvious, but make your connectors appear as connectors. A good schematic should keep all the pins in order, and have all connectors clearly drawn in. Remember, what is easy to identify is easy to follow.

Summary

Your software is an essential tool in designing your board. But so is ensuring that all your logic is visible, and easy to recall. Using these steps will help ensure that any potential design issues are easy to identify and resolve.