Embedded system Jaapson PCB

An embedded system is a computer system with a dedicated function within a larger mechanical or electrical system, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. Embedded systems control many devices in common use today.

Properties typical of embedded computers when compared with general-purpose ones are e.g. low power consumption, small size, rugged operating ranges and low per-unit cost. This comes at the price of limited processing resources, which make them significantly more difficult to program and to interface with. However, by building intelligence mechanisms on the top of the hardware, taking advantage of possible existing sensors and the existence of a network of embedded units, one can both optimally manage available resources at the unit and network levels as well as provide augmented functionalities, well beyond those available. For example, intelligent techniques can be designed to manage power consumption of embedded systems.

 

Modern embedded systems are often based on microcontrollers (i.e. CPUs with integrated memory or peripheral interfaces) but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also still common, especially in more complex systems. In either case, the processor(s) used may be types ranging from general purpose to those specialized in certain class of computations, or even custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor (DSP).

Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase the reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale.

 

Embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, and largely complex systems like hybrid vehicles, MRI, and avionics. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure.

 

 

 

 

Baggio WANG FAN

-----------------------------------------------------------

SHENZHEN JAAPSON TECHNOLOGY CO LTD

Building 2, Tongfuyu Industrial Park,Shenzhen, China, 518104

Tel: 86-755-82596922

Fax:86-755-82596922/82596923

skype: baggiowang0214

baggio.wang@funsunpcb.com

baggio@jaapson-pcb.com 

www.jaapsonpcb.com

JAAPSON, The Expert in HDI Multi-layer PCBs

multi-layer-pcb-embedded-technology

Baggio WANG FAN

-----------------------------------------------------------

SHENZHEN JAAPSON TECHNOLOGY CO LTD

Building 2, Tongfuyu Industrial Park,Shenzhen, China, 518104

Tel: 86-755-82596922

Fax:86-755-82596922/82596923

skype: baggiowang0214

baggio.wang@funsunpcb.com

baggio@jaapson-pcb.com 

www.jaapsonpcb.com

JAAPSON, The Expert in HDI Multi-layer PCBs

Multi-layer-HDI-PCB-JAAPSON

 

 

 

 

Baggio WANG FAN

-----------------------------------------------------------

SHENZHEN JAAPSON TECHNOLOGY CO LTD

Building 2, Tongfuyu Industrial Park,Shenzhen, China, 518104

Tel: 86-755-82596922

Fax:86-755-82596922/82596923

skype: baggiowang0214

baggio.wang@funsunpcb.com

baggio@jaapson-pcb.com 

www.jaapsonpcb.com

JAAPSON, The Expert in HDI Multi-layer PCBs

 

Gold plating on connectors

JAAPSON(www.jaapsonpcb.com) offers two types of gold finish: Electroless Nickel Immersion Gold (ENIG) as a surface finish for the whole PCB, and hard plated gold over plated nickel for edge-connector fingers. Electroless gold gives excellent solderability, but the chemical deposition process means that it is too soft and too thin to withstand repeated abrasion. Electroplated gold is thicker and harder making it ideal for edge-connector contacts for PCBs which will be repeatedly plugged in and removed.

 

We plate the hard gold onto the PCBs after the soldermask process and before we apply the surface finish to the rest of the board. Hard-gold plating is compatible with all the other surface finishes we offer.

 

 

We first plate 3 – 6 microns of nickel onto the edge connector fingers and then on top of that 1 – 2 microns of hard gold. The plated gold is not 100% pure; it contains some cobalt to increase the wear-resistance of the surface.

We normally bevel the edge connectors to ensure easy insertion. Bevelling can be specified in the order details.

To make sure that the gold fingers align exactly with the edge-connector profile, we rout the vertical edges of the connector on the first drill run. The edges of the connector are then exactly aligned to the printed image.

In some cases one or more gold fingers are shorter than the rest, so that the longer pads connect first when the PCB inserted into the connector. This means that the shorter pads cannot be connected vertically to the plating bar. They have to make the connection needed for electroplating in another direction (see illustration. Here the blue lines represent the profile added at first drill stage and the green the final profiling).

Limitations of the technology

The plated pads have to be on the edge of the PCB, as this is an electroplating process. There has to be an electrical connection between the plated pads and the production panel frame.

 

The maximum length of the plated pads is 40 mm as we use a standard shallow plating bath .

 

Inner layers have to be free of copper at the edge of PCB. Otherwise the bevelling could expose the copper.

If you want your PCBs delivered in a customer panel, the panel frame/border must be open on the edge connector side to allow us to make the connection for electroplating.

 

 

We can plate hard gold on two sides of PCB. But if the connectors are on the opposite sides of the PCB there has to be a minimum 150 mm between them.

To ensure optimum quality surface-finish, do not place any plated holes (PTH), SMD or other pads closer than 2.00 mm (80 mil) to the gold fingers – see drawing.

 

 

 

 

Baggio WANG

-----------------------------------------------------------

SHENZHEN JAAPSON TECHNOLOGY CO LTD

Building 2, Tongfuyu Industrial Park,Shenzhen, China, 518104

Tel: 86-755-82596922

Fax:86-755-82596922/82596923

skype: baggiowang0214

baggio.wang@funsunpcb.com

baggio@jaapson-pcb.com 

www.jaapsonpcb.com

JAAPSON, The Expert in HDI Multi-layer PCBs

controlled impedance PCB

As PCB signal switching speeds increase today's PCB designer needs to understand and control the impedance of PCB traces. With the short signal transition times and high clock rates of modern digital circuitry, PCB traces need to be considered not as simple connections but as transmission lines.

What is controlled impedance?

Probably the most common example of a controlled impedance component is the downlead (or feeder) connecting a receiving aerial to a wireless or television set. Aerial feeder leads usually take the form of "flat twin" cable (commonly supplied with VHF broadcast receivers) or low-loss coaxial cable. In both cases the impedance of the feeder is controlled by the physical dimensions and material of the cable.

So why do we need to control impedance?

The receiving aerial possesses a natural, or characteristic, impedance and electrical theory shows that for the aerial to transfer maximum power to the set (and to ensure the integrity of the electrical signal) the impedance both of the feeder and the receiver should match that of the aerial. In other words the signal should ideally be presented with a constant impedance as it travels from its source to its destination. Where a mismatch occurs only part of the signal will be transmitted; the rest will be reflected toward the source (this degrades the signal). Cable designers therefore take great care to ensure the accuracy and consistency of the cable dimensions and material characteristics. At high signal switching speeds, the electrical properties of the cable, such as the capacitance and inductance, must be taken into account, and cables can no longer be considered as simple wires. Cables designed for high signal speeds where these factors are taken into consideration are referred to as transmission lines.

Controlled impedance on PCBs

Similarly, as the speed of signal switching on a PCB increases, the electrical properties of the traces carrying signals between devices become increasingly more important. The impedance of a PCB trace is controlled by
its configuration
dimensions (trace width and thickness and height of the board material)
dielectric constant of the board material

As with a cable, when the signal encounters a change of impedance arising from a change in material or geometry, part of the signal will be reflected and part transmitted. These reflections are likely to cause aberrations on the signal which may degrade circuit performance (e.g. low gain, noise and random errors). In practice board designers will specify impedance values and tolerances for board traces and rely on the PCB manufacturer to conform to the specification.

Testing the PCB

Most controlled impedance PCBs undergo 100% testing. However, it is not uncommon for the actual PCB traces to be inaccessible for testing. In addition, traces may be too short for accurate measurement and may well include branches and vias which would also make exact impedance measurements difficult. Adding extra pads and vias for test purposes would affect performance and occupy board space. PCB testing is therefore normally performed, not on the PCB itself, but on one or two test coupons integrated into the PCB panel. The coupon is of the same layer and trace construction as the main PCB and includes traces with precisely the same impedance as those on the PCB, so testing the coupon affords a high degree of confidence that the board impedances will be correct.

Measuring controlled impedance

Impedance measurements are usually made with a time domain reflectometer (TDR). The TDR applies a fast voltage step to the coupon via a controlled impedance cable and probe. Any reflections in the pulse waveform are displayed on the TDR and indicate a change in impedance value (this is known as a discontinuity). The TDR is able to indicate the location and scale of discontinuity. Using appropriate software the TDR can be made to plot a graph of the impedance over the length of the test trace on the coupon. The resulting graphical representation of the trace characteristic impedance allows previously complex measurements to be performed in a production environment.



SHENZHEN JAAPSON TECHNOLOGY CO LTD
Building 2, Tongfuyu Industrial Park,Shenzhen, China, 518104
Tel: 86-755-82596922
Fax:86-755-82596922/82596923
sales@funsunpcb.com
baggio@jaapson-pcb.com
www.jaapsonpcb.com