Friday, July 11, 2008

PCB Material

FR- Flame Retardant
FR-2 Phenolic Cotton paper
FR-3 Cotton paper and epoxy
FR-4 Woven Glass and epoxy
FR-5 Woven Glass and epoxy
FR-6 Matte Glass and epoxy
G-10 Woven glass and epoxy
CEM-1 Cotten paper and epoxy
CEM-2 Cotten paper and epoxy
CEM-3 Woven Glass and epoxy
CEM-4 Woven Glass and epoxy
CEM-5 Woven Glass and epoxy
Polyimide

Friday, February 29, 2008

Read this doc on Scribd: Microsoft Word - Pdock handout

Saturday, February 04, 2006

Sunday, December 11, 2005

Open source Schematic capture program for Windows

TinyCAD is a program to help you draw circuit diagrams. It comes complete with symbol libraries to get you started straight away. As well as being able to simply print your designs, you can use TinyCAD to publish your drawings by copying and pasting into a Word document, or saving as a PNG bitmap for the web.

You can use TinyCAD as a front end to a PCB layout program (see the links), by getting TinyCAD to create a netlist of your circuit.

TinyCAD is fully open-source so you can use it for free and you can download the source code for use in your own projects.

Friday, June 10, 2005

PCB TERMS

Aperture
This is a text file describing the size and shape of each element on the board. These are also known as a D-code lists. These lists are not necessary if your files are saved as Extended Gerber with embedded Apertures (RS274X).

Aspect Ratio
Standard aspect ratio of 6:1 has been figured into our quote forms. This equals the smallest hole size that can support plating. It is calculate by taking the board thickness divided by the smallest drill diameter.

Board Thickness
Standard base thickness is 1/16 inch, which is also called out as 0.062" or 0.059" 0.031", 0.047", 0.093", and 0.125". A typical tolerance is within 10% of the given thickness.

Clearances
A clearance (or isolation) is a term use to describe the space from power / ground layer copper to through hole. To prevent shorting, ground and power layer clearances need to be .025” larger than the finish hole size for the inner layers. This allows for drilling, and plating tolerances.

Component Side
In order to prevent building a board inside out, . Component, layer 1, or 'top' layer should read in facing up. All other layers should line up as though looking through the board. Use layer designators, pass through marks, or correct reading layer text.

Copper (Finished Copper)
This is how much copper your board will have on its surface. It is the copper foil thickness, plus plated copper, minus surface preparation. It is given in oz / per sq foot. 1 oz = a minimum of 0.0012”- 0.0014” thickness.

Cut lines
The cut line is going to be used to program the router path and it represents the board outside edge. Typical route tolerance is +/- 0.010". It is recommended to keep outer layer copper 0.01” and inner copper 0.025” from the cut line to avoid contact with the board edge.

HAL
Acronym HAL, which is the process of putting solder on exposed copper of the circuit board. Approx. 60/40 Tin/Lead mix is used. Also known as a SMOBC which is an acronym for Solder Mask Over Bare Copper.

Pad Sizes
Your outer layer pads need to be 0.017" larger than the finish tool size (0.010” for vias). Your inner layer pads need to be 0.018" larger than your finished tool size. If your design has any pad to trace junction minimum requirement, add that to the above numbers [0.017" pad + 0.002" junction should have 0.019" pad].

Silk Screen, Nomenclature, or Legend (Artwork)
Marking ink is used to identify components during later assembly and troubleshooting processes. This can be placed on one or two sides (in yellow or white), depending on the board design and application. We can include your company logo if it is provided on the drawing specs.

Friday, May 06, 2005

What is PCB?

A printed circuit board or PCB interconnects electronic components without discrete wires. Alternative names are printed wiring board or PWB.

A printed circuit board consists of "printed wires" attached to a sheet of insulator. The conductive "printed wires" are called "traces". The insulator is called the substrate, and is made of "Pertinax" (a phenol formaldehyde resin) or a fiberglass-reinforced epoxy composite material.

A few printed circuit boards are made by adding traces to the substrate. The vast majority are manufactured by gluing a layer of copper foil over the entire substrate, sometimes on both sides, (creating a "blank PCB"), then removing unwanted copper, leaving only the copper traces. Some PCBs have a trace layer inside the PCB ("multi layer").

After the circuit board has been manufactured, components are attached to the traces by soldering.

There are three common methods used for the production of printed circuit boards:

1. Photoengraving, the use photomask and chemical etching to remove the copper foil from the substrate. The photomask is usually prepared with a photoplotter from data produced by a technician using computer-aided PCB design software. Some people produce low-resolution photoplots by printing a design to a laser printer, printing on the sheets used to make transparent presentations.
2. PCB Milling, the use of a 2 or 3 axis mechanical milling systems to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper' operates similar to a plotter, it receives commands from the host software package that controls the position of the milling head in the X/Y and sometimes Z axis. Data to drive the Prototyper is extracted from files generated in PCB design software.
3. PCB Printing, the use of conductive ink or epoxy to form traces directly on substrate material. Is similar to PCB milling in terms of hardware and data used.

PCBs are rugged, inexpensive, and can be highly reliable. They are harder to repair than wire wrap boards. They require much more design than either wire-wrapped or point-to-point constructed equipment.

Wednesday, April 20, 2005

Current carrying capacity of tracks

In the table the following are assumed

* 1oz/sq foot copper (0.035mm thickness).
* 10 degree C rise on outer layers, 20 degree C inner layers
* Groups of high current tracks will be de-rated
* Tracks are not near or over 'Heat Sink' areas

Imperial Width Metric Width Current Capacity

0.010" 0.25mm 0.8 Amps

0.015" 0.38mm 1.2 Amps

0.020" 0.50mm 1.5 Amps

0.050" 1.27mm 3.2 Amps

0.100" 2.5mm 6.0 Amps

For most purposes it will be easy to determine a practical width from the above. If you want to make more precise calculations (based, it must be noted, on empirical data) try the formula
I = 0.048 T0.44 A0.725
Where the units are

I Amps

T Temperature Rise in °C

A Cross sectional area in square mils (square THOU)

This formula is for outer layers, and needs to be de-rated to 50% for inner layers.
References to this formula can be found Here in the section PCB Data.

Thursday, April 07, 2005

How PCB is manufactured

Printed Circuit Board (PCB) are manufactured through a series of phot imaging and etching processes. For a start we need a schematic of the circuit to be created in a CAD software, from this schematic a "Gerber Data file is created and then is converted via computer aided manufacturing software (CAM) to form the basic layout of the Printed Circuit board itself.

CAM software will generate the artwork with the aid of a plotting machine, these artwork will be use in the PCB manufacturing process.

Circuit board materials like FR4, Polymide, Getek etc comes in various sizes which have to be pre cut into specific panel dimensions depending of the amount of boards to be layout on the panels. For multilayer boards, each layer is make just like making multilayer cakes, layer by layer and finally bake in an oven.

The panels are first coated with light sensitive film, and the images from the artwork are printed on the coated panels. Through a process of etching the unwanted areas of the panel copper are removed, leaving only the circuit traces. All the other layers are process in the same manner.

The etched layers are then laminated together by pressing them with thin sheets of resin coated fiberglass under high pressure and high temperature. When the board cools the layer are bonded together. Holes are drilled using the drill data file from the Gerber output. Through hole plating is then performed to connect the various layer of each hole to make electrical contacts.

The next step is to provide a coating of solder mask to the panels in order to protect the circuitry from receiving any solder during assembly. This process covers the circuitry to leaves the holes and/ or surface mount tabs (smt) exposed so they can receive solder during assembly.

Final processes include fabrication of each panel where each board is cutout of its panel and; electrical test, where each board is individually tested for opens and shorts, Before shipment to the customer, each part is inspected for workmanship and quality.

Saturday, February 19, 2005


pcbflow Posted by Hello

Saturday, February 12, 2005

History of PCB

PAUL EISLER

1907 Paul Eisler born.
1930 Qualified in Engineering at Vienna University.
Installing radios into trains in Belgrade and also work as a printer
1934 lost his job
1936 left for England
1943 Patent printed circuits
1945 After end of Second World War USA release secret of printed circuit board.
1948 All electronics in airborne instruments use printed circuit boards.