Wednesday, August 7, 2013

Advanced design navigation feature

Advanced design navigation feature



As designs increase in size and complexity, the ability to navigate project documents becomes ever more important. For the designer working to a stringent deadline, being able to smoothly interrogate Nets, Pins, Ports, Parts and Power Supplies within the design, with minimal effort, is paramount. One way to achieve this in Altium Designer is by using the Navigator panel. This panel presents the constituent elements of the design in tabular format, and allows quick highlighting of parts, pins and nets on source schematics or target PCB. In addition, supporting dynamic, bi-directional component cross-selection, Altium Designer offers its Cross Select Mode feature. With this feature enabled, the designer can simply click to select one or more components in one domain and those same components will become selected in the other domain. In this Design Secret video, we present the basic functionality of the Navigator panel and how, when used in combination with the Cross Select feature, you can navigate your design projects in a far more efficient and streamlined manner.

Play Video (4:38:00)


Tuesday, August 6, 2013

Announcement: Texas Instruments Precision Op Amps Released!

The Content Team is pleased to announce the second Amplifier & Linear board-level library release for Texas Instruments. At the end of July we released more than 4500 additional operational amplifiers covering the entire ‘Precision Amplifier’ catalog. Our support for TI’s wide range of op amps now includes more than 7000 supply-chain enabled, board-level components.

In the previous TI release we covered General Purpose (1448) and High Speed Amplifiers (1100). Adding Precision Amplifiers (4599) now completes the majority of the Operational Amplifier catalog (excluding the NSC parts which we will merge and update soon!) These three, broader op amp categories cover the lion’s share of TI op amps - and include the following sub-families:

High Speed (>=50MHz)

Fully Differential Amplifier

Zero Drift Precision Amplifier

Low Noise Amp (<=10nV/rtHZ)

Low Power Amp (<=500uA)

Low Input Bias Current Amp (<=10pA)

Low Offset Voltage Amplifier (<=500uV)

High Supply Voltage Amplifier (>=30V)

General Purpose

Low Supply Voltage Amplifier (<=2.7V)

High Output Current Amplifier (>=50mA)

Precision Amplifier

Audio Operational Amplifier

Many op amps are cross classified, so we’ve included a ‘Sub Family’ parameter to capture this, and hopefully make it easier to search in the vault.

We’ve now developed components for more than 25,000 TI parts, and all are available in the Altium Content Vault and as Design Content libraries available here. You can also place these components directly from within Altium Designer via the Vault Explorer - where you will also find live supplier links and pricing information from suppliers such as Digi-Key, Farnell/Newark, Mouser and more - connect to the Altium Content Vault to explore further.


Friday, August 2, 2013

Ruminating Rigid-Flex - Part 1

Ruminating Rigid-Flex - Part 1


Altium Designer, flexible circuits, flex, rigid, rigid-flex, polyimide, polyester, printed circuits, film, paste, deposition, PCB, coverlay, adhesive, fabrication, materials, glass, fibreglass, fibre, resin, epoxy

As the title of this blog suggests, I've been thinking a lot lately about Rigid-Flex circuit boards. Rigid-Flex can have many benefits, and many designers are at least considering it today who previously did not have to. It seems that more designers are facing higher pressures to build ever more densely populated electronics, and with that also comes pressure to reduce costs and time in manufacturing. Well, this is really nothing new of course. It's just that the scope of engineers and designers having to respond to these pressures is continuously broadening.

But there are aspects of rigid-flex which could be pot-holes in the road for newcomers to the technology. So it's wise to first understand how flex circuits and rigid-flex boards are actually made. From there we can look at the design issues and find a clear path forward. For now, let us consider what basic materials go into these boards.

Flex-circuit materials

Substrate and Coverlay Films

Start by thinking of a normal rigid PCB - the base material is typically fibreglass and epoxy resin. It's actually a fabric, and although we term these "rigid" if you take a single laminate layer they have a reasonable amount of elasticity. It's the cured epoxy which makes the board more rigid. This is not flexible enough for many applications though for simple assemblies where there's not going to be constant movement it is suitable.

For the majority of applications, more flexible plastic than the usual network epoxy resin is needed. The most common choice is polyimide, because its very flexible, very tough (you can't tear or noticeably stretch it by hand, making it tolerant in product assembly), and also incredibly heat resistant. This makes it highly tolerant of multiple reflow cycles and reasonably stable in expansion and contraction due to temperature fluctuations.

Polyester (PET) is another commonly used flex-circuit material, but it's not tolerant of high temps and less dimensionally sound that Polyimide (PI) films. I have seen this used in very low cost electronics where the flexible part had printed conductors (where the PET could not handle the heat of lamination), and needless to say nothing was soldered to it - rather, contact was made by crude pressure. I seem to remember that the display in this product (a clock radio) in question never really worked too well due to the low quality of the flex circuit connection. So for rigid-flex we'll assume we're sticking to the PI film. (Other materials are available but not often used).

PI and PET films, as well as thin epoxy and glass fibre cores, form common substrates for flex circuits. The circuits must then use additional films (usually PI or PET, sometimes flexible solder mask ink) for coverlay. Coverlay insulates the outer surface conductors and protects from corrosion and damage, in the same way solder mask does on the rigid board. Thicknesses of PI and PET films range from mil to 3 mils, with 1 or 2 mils being typical. Glass fibre and epoxy substrates are sensibly thicker, ranging from 2 mils to 4 mils.


While the above-mentioned el-cheapo electronics may use printed conductors - usually some kind of carbon film or silver based ink - copper is the most typical conductor of choice. Depending upon the application different forms of copper need to be considered. If you are simply using the flexible part of the circuit to reduce manufacturing time and costs by removing cabling and connectors, then the usual laminated copper foil (Electro-Deposited, or ED) for rigid board use is fine. This may also be used where heavier copper weights are desired to keep high-current carrying conductors to the minimum viable width, as in planar inductors.

But copper is also infamous for work-hardening and fatigue. If your final application involves repeated creasing or movement of the flex circuit you need to consider higher-grade Rolled Annealed (RA) foils. Obviously the added step of annealing the foil adds to the cost considerably. But the annealed copper is able to stretch more before fatigue cracking occurs, and is springier in the Z deflection direction - exactly what you want for a flex circuit that will be bending or rolling all the time. This is because the rolling annealing process elongates the grain structure in the planar direction.

Figure 2: Exaggerated illustration of the annealing process, obviously not to scale. The copper foil passes between high-pressure rollers which elongate the grain structure in a planar orientation, making the copper much more flexible and springy in the z-deflection.

Examples of such an application would be gantry connections to a CNC router head, or laser pickup for a Blu-Ray drive (as shown below).

Figure 3: Flex-circuit used to link the laser pickup to the main board assembly in a Blu-Ray mechanism. Notice that the PCB on the laser head has the flexible portion bent at right angles, and an adhesive bead has been added for strengthening the flex circuit at the join.


Traditionally, adhesives are required for bonding the copper foil to PI (or other) films, because unlike a typical FR-4 rigid board, there's less "tooth" in the annealed copper, and heat & pressure alone are not enough to form a reliable bond. Manufacturers such as DuPont offer pre-laminated single- and double-sided copper clad films for flexible circuit etching, using acrylic or epoxy based adhesives with typical thicknesses of ½ and 1 mil. The adhesives are specially developed for flexibility.

"Adhesiveless" laminates are becoming more prevalent due to newer processes that involve copper plating or deposition directly onto the PI film. These films are chosen when finer pitches and smaller vias are needed as in HDI circuits.

Silicones, hot-melt glues, and epoxy resins are also used when protective beads are added to the flex-to-rigid joins or interfaces (i.e. where the flexible part of the layer stack leaves the rigid part). These offer mechanical reinforcement to the fulcrum of the flex-to-rigid join which otherwise would rapidly fatigue and crack or tear in repeated use. An example of this is shown in Figure 3 above.

Figure 4: Typical single-layer Flex Circuit stack-up.


It's important to be aware of the materials used in flexible and rigid-flex circuits. Even though you may generally allow the fabricator freedom to select the materials based on your application, ignorance will not protect you from field-failures of the final product. A really good resource which contains far more detail than my brief introduction here is Coombs, C. F. (Editor, 2008) The Printed Circuits Handbook, 6th Ed. 2008 McGraw Hill, pp 61.3 0 - 61.24.

Knowing the material properties will also help in the mechanical design, evaluation and test of your product. If you are working on automotive products for instance; heat, moisture, chemicals, shock & vibe - all need to be modelled with accurate material properties to determine the product's reliability, and minimum allowed bending radius. The irony is that the driving needs that cause you to choose flexible and rigid-flex are often tied to harsh environments. For example, low-cost consumer personal electronic devices are often subjected to vibrations, dropping, sweat and worse.

In the next installment of this blog, we'll look at the fabrication steps in rigid flex circuits, which will lead to better understanding of the design considerations, to be explored in a subsequent post.