Easy understand the PCB layout

PCB layout is laying conductive signal path connecting the various devices, like decorate the  road, connecting the city by car.
Road construction requires a return to a two-line, PCB routing the same principle, you need two lines form a loop ,for the low-frequency circuit point is a circuit; for the electromagnetic field in terms of speed it is  the transmission line, the most common, such as differential signals line. Such as USB, cable, etc.

We can say that the differential signal lines, is the ideal model for connecting devices signals. The higher the signal requirements, the more you want to close the differential signal lines.

When the device is very much in a board, if distribute it as the differential lines: one problem is PCB area is too large, the second problem is should be distribute into 2N lines heavy workload, It is very difficult, so the actual needs of the people for the proposed multi-layer PCB the concept, The typical is the double-sided PCB board. The bottom layer as a common reference circuit wiring ,so only distribute N + 1 lines, PCB layout is also greatly reduced

Common reference circuit, we often say that the reference ground, for most embedded industry, because the signal is digitized ,signal quality requirements is not very high. Using whole Layer of reference ground not only reduce the board size, but also improve efficiency , it saves time. In fact, the board is reduced to shorten the length of the signal line, and some may be offset because the reference to the signal quality degradation caused problems, so in practice, such incorporation by reference to the effect of PCB layout, the difference was similar to the ideal model line

In the dual-panel design, usually there are often cross-line, you need to do cross-line jumper to ground switching, noted that this jumper can not too long, if too long, easy to split reference ground, especially for some signal line high quality requirements, refer to the bottom it can not be split. Otherwise the signal circuit was completely destroyed, reference ground line will be useless.  generally speaking,  reference ground line only suitable for short jumper with signal lines, signal cables distribute on top layer, or use  more layers of PCB board


PCB layout carrier is a PCB board, general reference  ground to  the PCB edge 1mm from nearby, the signal from the reference line to the near edge of 1mm, so the signals are confined within the PCB  board, this way can be reduced EMC radiation

Source:http://www.wonderfulpcb.com/blog/easy-understand-pcb-layout/

PCB Circuit Board Welding Tool

PCB circuit board welding main tools: manual welding is an electronic assembly must master the technology, the correct selection of solder and flux, according to the actual situation of choice of tools, is to ensure the quality of the necessary conditions.

Solder: fusion of two or more than two kinds of metal, to become a whole fusible metal or alloy called solder. Commonly used in tin lead solder, tin (62.7%), lead accounted for 37.3%.

The ratio of the solder melting point and freezing point is 183 C can by direct liquid cooling to a solid state, not through the semi liquid solder joints can be solidified rapidly, shortening the welding time and reduce weld, the temperature said for the eutectic point, the composition of solder said eutectic solder.

Eutectic solder has a low melting point, melting point and solidification point, good fluidity, small surface tension, good wettability, high mechanical strength, solder joints can withstand the larger tensile and shear, good conductive properties.

Flux

Flux is a welding auxiliary materials, the role is as follows: l oxide film is removed. L to prevent oxidation. L decrease surface tension. L solder joint appearance.

Commonly used flux is rosin, rosin alcohol flux, solder paste, flux of zinc chloride, ammonium chloride flux. Welding often used center clip rosin flux, tin content for 61% of the 39 tin lead solder wire, also known as rosin solder wire

Selection of welding tools:

General electric irons: ordinary electric iron welding is only suitable for less demanding applications. Such as welding wire, cable and so on.

Constant temperature electric iron: the important characteristics of the constant temperature electric iron is a temperature control device, makes the welding temperature stability, used for welding of PCB board is fine.

Desoldering: Tin suction device is actually a small manual air pump, pressure suction tinware of pressure bar, discharge the suction tinware cavity air; release ceiling tinware pressure rod lock button spring to push the pressure rod quickly return to the in situ, in the solder sucker is formed in the cavity air negative pressure, can suck the molten solder.

Hot air gun: hot air gun, also known as SMD electronic components desoldering station. It is specially used for patch surface mounted electronic components, especially the multi pin SMD IC soldering and dismounting. Recommended tripod BGA welding table adopts imported hot air gun, and cheap.

What is the pcb cost making up

Pcb manufacture is now more and more knowing in pcb line. Customer from all over the world would need pcb manufacture. China is the biggest pcb manufacture export country in the world. As a result, many pcb factories and pcb exporters in China.

As the customers are from different kinds of company and they may not know too much about pcb except they are pcb manufacturing or the engineers which would know much about pcb cost. People from different countries would have their own feeling about the pcb cost. But in China, our pcb cost would includ pcb engineer cost, pcb price, flying testing fees, film fees and fixture cost. Sometimes when i make a quote to the Germany customer. He may not understand the enginner cost and tooling cost. Actually the engineer cost is called tooling cost in some way. For some customers, they totally don’t understand why the pcb cost should contain so much items. They may know the pcb price. So you need to explain very professionally to persuade them to buy your pcb.

I think it is vey difficult to explain pcb cost to a customer who know little about pcb. So it would cause a bad effect to your negotiate. You customer may feel you are not reliable and make the quote in higher price and you may lose your customer.

So i think it is better to separate your clients in different parts. Some is good knowing pcb cost and some is not. When you are not sure you had better to make sure before you quote to your customer. If he is not likely to see the pcb engineering cost, you can try to share the pcb engineer cost into the unit pcb price. You just tell them the quantity and the each pcs cost and it is okay.

PCB manufaturer is very simple but you don’t require your customer to know all about the pcb. Like the pcb cost, you should try to know before the client and choose a acceptable way to make him a quote.

PCBA coated area attentions

Currently there is no specific provisions for the PCBA coated area in the industry, and each customer's requirements are not necessarily the same.

Requirements for most products as follows

PCBA coated areacan not be:

1. The need for regional electrical connections, such as the gold pad, Goldfinger, metal vias, test holes and the like;

2. The batteries and battery holder;

3. The connector;

4. The fuse and housing;

5. The cooling device;

6. Jumper;

7. The lens of the optical device;

8. potentiometer;

9. The sensor;

10. No sealed switch;

11. The other regions will be affected by the coating performance or operation.

The area to be coated （PCBA coated area）:

In addition to the above-mentioned area, all other open solder joints, leg, conductor some components should be coated.

Three anti-paint sprayer machine helps a lot for PCBA coated area painting. The machine greatly improved the quality of the three anti-paint spraying and spraying efficiency for the enterprise to solve the recruitment difficulties (difficult to recruit professionals), and quality issue s. There is an operation manual is strongly recommended. Use sprayer is to bring a lot of convenience. But there are some problems that need attention:

1, spraying environmental requirements: All spraying operations should not be below 16 ℃and relative humidity less than 30% of the conditions. If the temperature is too low it can be heated in an oven at 40 degrees 30 minutes after the spraying, optimum temperature 30 C. High humidity is also using the same method and the same conditions heating.

2, PCB board requirements: to be sprayed PCB board subject to testing, testing, debugging qualified, and thoroughly carried out (solder, rosin, dust, oil, flux and residue) after the cleaning process clean. Do not allow spraying device, to provide a fast-drying and easy peel masking tape, protection-related components (these components include connectors, IC sockets, adjustable potentiometers, high power radiators, test point, the connection point) Cycling clothes.

3, workers protection requirements: workers should wear splash goggles and isolating gloves and wear protective masks.

4, PCB board coating area must be flat, use jigs and other tools, the spout from the target 20--30cm uniform coating, the coating is thin and uniform. Spray the surface to ensure complete coverage of the three anti-paint, spray can face and eyes in a plane to see whether complete spraying.

5, after the first pass three paint is completely dry (1 hour) for the second spraying, spraying refer to step 4.2.

It is very Important that this is not only the PCBA coating area quality assurance, but also a secure protection for the operator.

For more informations about PCBA