Archive for June, 2016

PCB Testing: Why is it Important?

Written by Rush PCB Inc on . Posted in PCB

PCB Testing.

In any manufacturing process, testing is a central element of the operation. Without robust testing processes, there is a risk of not identifying defects that could potentially cause products to fail, once they’re in the market. The long term outcome will be a poor reputation for your brand, and reduced customer confidence.

PCBs are central to the effective operation of electronic devices. To ensure the whole device works as planned, it is vital that they are comprehensively tested.  With PCB design, testing needs to be incorporated into each stage of the design process. There are specific test procedures that need to be conducted as part of the process.  Testing is more effective than identifying an error late in the development process or after the product has gone to market.

There are various tests for PCBs. The in-circuit test (ICT) method is a popular strategy for delivering fault diagnosis at a component level. It is cost effective, and helps identify issues with PCBs before they are integrated into larger units. ICT is a very accurate test process.

Specialist Automated Test Equipment (ATE) conducts a ‘manufacturing defect analysis’ (MDA). The testing validates each component on the PCB, and verifies passive control measurement, the orientation of diodes and transistors, and supply voltage. It also looks for open and short circuits. Tests can involve basic functional process validation as well as ‘vectorless’ test that check the PCB pins. Analogue and Digital measurements can be tested.

There is a cost for setting up an ICT – usually around $10-13,000. This investment provides a ‘bed of nails’ fixture. Because of this relatively large one-off fee, the method is suited to high volume manufacturing, generally when the designs are stable.  While the initial cost is high, the ongoing cost for each unit is low. As a guide, a medium sized board can be tested in less than a minute, and at a cost per board of less than $1.50.

 

If there is a change to the PCB design, then new equipment will be required.  Therefore, it is important that the PCB has been designed to allow for the testing. Keeping configurations simple by separating all components from the test pads is an example of optimizing the layout. For example, keep all components on one side of the board while test pads are on the other. There are fixtures that will allow probing of both sides, but using these increases the cost and the time to debug.

There are technical requirements for an ICT. A 0.05” test pad for each net needs to be incorporated into the PCB design. Spacing is important, as using appropriate spacing allows for the use of robust, long lasting test pins. The pads need to be at least 0.125” from the edge of the PCB, and 0.1” apart from any other component and each other.  There needs to be space on the component side for the ‘pusher rods’ to be pressed down.

The test will be most effective when the board is provided in conjunction with a bill of materials, CAD and appropriate schematics. The data from the CAD will be used to generate the basic test program. This ensures that there is no manual interpretation of the board, but the information is sourced from the original design.

Debugging is achieved through using sample PCBs that are either populated or unpopulated. It includes ensuring that the PCB assemblies fit, physically, in their intended location.

Concept & Mechanical Designs of Flex & Rigid-Flex PCBs

Written by Rush PCB Inc on . Posted in PCB, PCB Design, PCB Manufacturing

Concept & Mechanical Designs _PCB

When considering flex and rigid-flex circuits, there are benefits for both the manufacturer and the OEM to both be involved in the concept development and design of PCBs. Developing an initial understanding of the project details will be crucial in delivery of an effective PCB development project. Communication between the customer’s project management and engineering team should be an early focus in delivery of an effective project.

Oddly Shaped Rigid-Flex PCB

We will seek to confirm whether a flex based solution is appropriate for your proposed application. It is possible that after a review of your requirements, we conclude that using a flexible circuit board may not be appropriate. Through our review process, we hope to be able to ensure the use of appropriate PCB technology. If this means that Rigid-Flex PCBs are not the most appropriate design for your requirements, we will let you know.

When designing Oddly Shaped Rigid-Flex PCBs, there are a number of factors that the manufacturer will need to know. These include:

  • Understanding what the designer is trying to achieve in the development of the PCB;
  • Identifying the functionality of the flexible PCB;
  • The general size and shape requirements of the board;
  • Determining whether the design is an active component or a point to point interconnect; and
  • Noting whether there are any special signal requirements (such as current carrying or impedance control).

Further detail may also assist in the design, such as knowing whether shielding is required (based on the environmental situation of the board); and whether there a radio frequency design is required. Once these questions have been addressed, we can provide you with a better understanding of how flex and rigid-flex PCBs can deliver solutions for your project.

Part of our process is identifying where additional functionality can be integrated at the design stage. We will also look for opportunities to integrate the separate parts of the design, and look for opportunities to simplify complex designs, which can reduce overall project costs.

Mechanical Design

The second stage of development of a Flex and Rigid-Flex design is ensuring that the mechanical design specifications are in place. We will need to clarify the following factors to ensure there is no risk of trace breakage once the board is inserted into the end product:

  • What the minimum bend requirements are for your PCB;
  • How the PCB is going to be bent to be positioned in your product; and
  • The flex section lengths required to meet the bend requirements.

Flexible PCB with Stiffeners

It is not possible to manufacture all shapes and configurations due to the processes involved in flex and rigid-flex manufacturing. In the same vein, it’s important to be aware that not all sizes are available, as very large parts can affect the dimensional stability and manufacturing tolerances. Therefore, we need to look at the shape and size of the flex part.

We can also add value by identifying options for mechanical design that you may not have considered. Examples include Stiffeners (required to support soldered connects and components, ensuring reliability and PSAs (double sided adhesive tape used to attach the flex). When considering PSA requirements, there are other factors to consider such as the whether the board will be used in high temperatures, whether the PSA needs to be thermally conductive, or to dissipate heat, and whether it needs to be electrically conductive to ground the part to the enclosure.

In some instances there may be requirements for shielding for RF or EMI sensitive applications. If so, consideration needs to be put around the form of shielding to be used (copper, silver ink, or special shielding films).

Finally, in some designs the flex circuit may need epoxy strain reliefs. These are required if there is a bend situated close to a stiffener or to the rigid PCB section.

PCB Trends 2016

Written by Rush PCB Inc on . Posted in PCB

pcb trend 2016

The first concept for a printed circuit board (PCB) was developed in the 1930s. The concept became commercially viable by the 1950s, and since then, PCBs have moved into just about every phase of our lives. They surround us, and have changed out lives in many ways. In the 2000s, trace was reduced to 3.5-4.5mil, and Flex and Rigid-Flex PCBs proved innovative. The ability of engineers and designers to use PCBs to infiltrate our lives continues on an ongoing basis.

Moore’s Law suggests that the number of transistors in a dense integrated circuit doubles approximately every two years. Moore made this claim in in1965. In the early 1970s, the RCA1802 was state-of-the-art, and able to deliver a whopping 2,500 transistors. Moore’s Law was shown to be validated when the Pentium chip was released in the mid-1990s, delivering five million transistors (5×106). 2010 saw the release of the Quad-core Z195, with 1,000,000,000 (1×109) transistors.

Based on Moore’s Law, we can anticipate chips having the capacity to deliver 6 x 1010 transistors by 2020. If that is to happen, then miniaturization will continue, unabated. The PCB industry will be challenged in basic process capability and in material properties to allow for ongoing developments that deliver improvements ininterconnection density and electrical performance. Moore’s Law has shown itself to be valid for the last 50 years, but if this is to continue to be the case, new concepts will need to be incorporated into PCB design.

Some current innovations in PCB design provide some insights into how those developments are happening. Some new developments that are facilitating this include Every Layer Interconnected (ELIC); High Density Interconnection (HDI).

ELIC design uses a method of stacking microvias on every layer. It provides the opportunity for dynamic connection between anytwo layers in a PCB. The level of flexibility provided by such a design maximizes the area available for use in dense component placement. It also provides increased circuit density when designers are faced with complex challenges in routing.

HDI is based on continually reducing in feature size the spacing and conductor width of trace, micro-via diameter and pitch. The aim inevitability is to incorporate more components and layers without compromising the size, weight or volume of the PCB. The electrical performance of the PCB will continue to be challenged by increased wireless bandwidth and increased processing speeds. However, there are concerns regarding the cost-benefit of incremental developments. One challenge is ensuring dimensional stability as individual isolation layers are reduced in thickness to 50 microns or less. Electrical performance is also affected, as signal performance and resistance to leakage are challenged at this level.

In addition to the use of HDI and ELIC, innovations include high aspect ratio products, high performance pulse plating copper, and the application of plasma technology. As each of these technologies are incorporated into PCB design, miniaturization will continue, and Moore’s Law may continue to be validated over the coming years.