Custom PCB board has to go through the flying probe test?

When Custom PCB board from China PCB manufacturer, does each board has to go through the flying probe test?

For small batch PCB system board, system board, will be on the model fly needle detection, if the test through will deliver the goods to you; for high-volume PCB system board, system board, will do a test needle plate tester for PCB test, than flying probe test more quickly fly. Because this can rest assured the sincerity of the PCB board manufacturer.

Flying probe test for PCB is the electrical test of some main problems the solution, mainly check PCB is open, short circuit; it used a probe to replace needle, using multiple driven by a motor, can fast moving electrical probe with the device pins make contact and electrical measurements were performed.

PCB Stack-Up Principle

PCB stack-up has a great influence on the EMC (electromagnetic compatibility) performance of a product. A good stack can reduce radiation from the loops on the PCB and the cables attached to the board. On the other hand, a poor stack-up can increase the radiation from both of these mechanisms considerably.

To design multi-layer PCB circuit boards, designers need to confirm the circuit boards structure firstly according to the scale of circuit, the size of circuit boards, and the requirements of electromagnetic compatibility (EMC). That is to say, designers have to use 2, 4, 6, or more layers of circuit boards. If the design requires the high density ball grid array (BGA) devices, the minimal number of wiring layers must be considered. For years, people always think that the less PCB layers would spend the lower cost. However, many other factors affect PCB manufacturing costs. In recent years, the differences between costs of multi-layer boards have been reduced significantly. As soon as the number of layers been determined, the placement of the inner layer and different signals in these layers are decided --- this is the stack-up design of multi-layer PCB. Careful planning and rational stack-up designs beforehand will save a lot of efforts in the following wiring and future production.

After the number of circuit board layers determined, It needs to reasonably arrange the placement order of the circuit of each layer. In this part, there are two main factors to be considered. One is the distribution of special signal layers. The other is the distribution of power layer and ground layer.
The more layers circuit boards have, the more varieties arrangement on special signal layers, ground layers and power layers have. Thus, it is more difficult to choose the best combination method, but the general principles are as follows

(1) The signal layer should be next to an internal power layer (internal power/ground layer), shielded by the copper film of internal power layer.

(2) The internal power layer should be integrated with ground layer tightly. That means, the thickness of medium between internal power layer and ground layer should take the smaller value, improving the power supply capacitor between the internal power layer and ground layer, and increasing the resonant frequency. If the electric potential difference between internal power layer and ground layer is not important, a smaller insulation thickness can be used, like 5mil (0.127mm).

(3) To avoid the two signal layers directly adjacent. It is easy to introduce crosstalk between adjacent signal layers, leading to the fail of the circuit. To place a ground layer between two signal layers can avoid cross talk efficiently.

(4) Multiple grounded internal power layers can reduce the ground impedance effectively. For example, A signal layer and B signal layer use ground plane respectively can reduce common-mode interference effectively.

(5) The symmetry of layer structure.

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PCB Design Considerations

In recent years, electronic products have been around military equipment , computers, communications equipment , mobile storage equipment, mobile communications equipment, and other related fields , and in size, integration, function and other aspects of the increasingly high demand , and consumer electronics in several generations per year the pace of development update , as an important part of the printed circuit boards and electronic products are constantly improve and update .  

 China now is the world's printed circuit board (PCB) production superpower , PCB species from single-sided to double-sided, 4-28 layer to multilayer ; from the through -hole conduction technology to blind hole conduction technology , Then HDI (High Density Interconnection) high density interconnect technology and technology progress. System board means is endless , different processes are different system boards also have advantages and disadvantages depending on the application object. Currently , the production of printed circuit boards are mainly used in two aspects, One enterprise production , the second is the school teaching and research .

In PCB design should pay attention to :

1 . Making physical borders:  closed physical borders of a future component placement , alignment is a basic platform , and also the layout automatically plays the role of constraint , otherwise , coming from the schematic elements will be overwhelmed . Here we must note accurately , otherwise after installation problems will be big trouble . There is a corner where the best arc , on the one hand to avoid sharp corners scratched workers , but also can reduce stress. 

2 . The introduction of component and networks: the network element and the introduction of good painting border should be very simple , but there are often problems must be solved one by one carefully follow the prompts errors , or later have to spend more effort.

3 , The layout element: lifetime layout and trace elements of the product , stability, EMC has great influence , should pay special attention to the place.

4 . Placed the order : the first place and the structure of the fixed location of the components, such as electrical outlets , lights , switches, connectors category , the placement of these parts LOCK function after a good software lock , will not make it in the future mistaken move . Then place a special element on the line and large components , such as the heating element , transformers , IC and so on . Finally, place a small device .

5 .Pay attention to heat : component placement pay special attention to heat issues . For high-power circuit , the heating element should be those such as power transistors , transformers, etc. try to place aside dispersed layout , easy heat dissipation , not concentrated in one place , nor too high capacitance in order to avoid premature aging of the electrolyte .

6. The wiring principle : when two panel wiring , two wires should be perpendicular , oblique , or curved alignment, avoiding parallel to each other , in order to reduce the parasitic coupling ; as the input and output circuits printed wire should try to avoid rabbit adjacent parallel , in order to avoid feedback between these wires plus ground wire is best . Traces corner as greater than 90 degrees , 90 degrees or less to prevent the corner , but also minimize the use of 90 -degree corners.

7 .Adjustment and improvement: after the completion of wiring to do is to text, individual components , traces some adjustments and copper , in order to facilitate production, commissioning and maintenance .

8 , checked for network ; sometimes because of misuse or negligence painted board network of relationships with different schematics , checking is necessary. So after drawing the plate must not rush to the manufacturer .

9 . Using the simulation function : so you can find some of the problems in advance , greatly reducing the workload for subsequent commissioning

So for China printed circuit board production enterprises should use traditional chemical system board technology for teaching and research universities and research institutions can use mechanical system board technology.

Printed circuit board (PCB) fixture test introduction

Rapidly increasing complexity of PCB assemblies makes visual defect detection nearly impossible. Receiving a PCBA without electrical verification can significantly delay design verification of prototypes and system integration of low volume PCBAs. The cost and time to develop fixture based in-circuit testing (ICT) is prohibitive in the prototype stage and the investment in ICT or functional test is tough to justify for low volume manufacturing. 

 

Vergent Products offers a solution – flying probe fixtureless testing based on parametric test of each component. Fixtureless test development is low cost and very fast. There is no costly fixture to design and build. Tests are generated from CAD information which enables a high degree of test coverage and flexibility. 

 

Testing your low volume products and prototypes allows for detection and repair of electrical defects such as wrong parts, reversed parts, missing parts, solder opens, and major solder defects. Fixtureless testing can help you improve your products time-to-market by achieving the highest possible quality levels early in the product life cycle. Fixtureless test allows your engineers to focus their efforts on prototype design verification instead of debugging process issues. 

 

Fixtureless testers use a flexible moving probe system. Multiple probes are automatically moved very rapidly to various test points on the assembly – hence the name: “flying probe”. These probes are capable of static DC voltage, current, resistance, capacitance, and inductance measurements. Test points are derived from CAD data to ensure accuracy and to maximize test coverage. 

    

Here is a brief description of some of the features of the Seica S40 has to offer: 

    1>Four independently moving topside contact probes; Test speeds up to 12 – 20 tests per second 

    2>Test area up to 16” x 20” 

    3>Positioning repeatability accuracy of +/- 0.12mils; Minimum positioning resolution of +- 0.20 mils in each axes 

    4>Minimum probe contact pitch of 0.12 mils between probe pins; Minimum pad size of 4.0 mils 

    5>Maximum component height of 0.9 inches including board thickness 

    6>Automated optical inspection, in-circuit programming, and boundary scan functional test capable (optional) 

 

For best turn around time on board test program generation and debug please provide: 

    1>Schematics 

    2>ASCII CAD data 

    3>Raw card 

    4>Populated board 

 

The test development NRE charges are very reasonable. 

introduction of circuit board drilling and PCB drilling File

A circuit board drilling is just like a common drill, except that it is optimized for drilling holes in the printed circuit board as opposed to drilling holes in other materials such as wood. To make a drill on PCB, the first factory should have the PCB drilling file. The drill file is also commonly referred to as an NC (numerically controlled) drill file in the industry. Excellon is the preferred term used with our Wonderful PCB Limited services. The Excellon drill file defines the hole locations and tool numbers (X & Y coordinates).

PCB drilling File General Requirements:

•All PCB holes are plated through meaning, there will be solder or silver in the PCB hole barrel.

•Must be Excellon format

•Must be ASCII text viewable. Please open with "Word" or "notepad" to verify a numeric list of X & Y coordinates. There should be no strange graphical characters.

•PCB drill file should not contain "G01", "G54", or any reference to "D" codes when opened in a text editor. This indicates a Gerber format and is most likely a drill drawing rather than an NC file.

•Properly formatted PCB drill files have sizes separated with "T" codes that indicate tool numbers. (T01, T02, etc)

•A tool report with sizes is necessary if the sizes are not included in the drill file header.

•For Slots or Cutouts (PCB Express only): Fabrication Drawing, NC Drill File, or Gerber file is necessary to define slot/cutout size and/or location. ◦To achieve a plated slot or cutout place the feature on the drill layer and include an outer layer pad at least the size of the slot or cutout.  Maximum diameter for a plated feature is 0.250"

To have PCB drilling file, and now we need to know there are two main drilling holes in the circuit board. One is NPTH hole, another is PTH hole.All the holes in the single sided printed circuit board are NPTH hole. That’s because no need for electronic conduction between layers in single sided PCB. It has just one copper foil layer. PTH hole will appear in double sided or multilayer PCB.

These holes exist for the electronic conduction among layers. So it may have Copper in these holes.

Back drilled holes can be back drilled before filling (no exposed copper), or after filling (exposed copper looking down on a cross-section of the barrel of the hole), or on non-filled holes. That means that they could be drilled before filling which means before the second drill for the unfilled holes (drill the identified back drill holes, plate, back drill, fill, drill non-filled holes, plate again) or after second plate (drill the filled holes, plate, fill, drill the identified back drill holes and the non-filled holes, plate, back drill the back drilled holes), or they could be back drilled at the end of all the processes if no holes have filling (drill all, plate, drill the back drilled holes).

There will be over size clearances for plane layers and there will be pad suppression for signal layers, so the only exposed copper is the "top" of the barrel. That should not be a problem in most applications and so back drilling (stub drilling) is not itself sufficient reason to incur the cost of via filling. But if VIAs are going to be filled, it makes sense to fill the holes but only before back drilling. Filling after back drilling has its own special issues.

Identifying the back drilled holes in a separate drill file or set of files, and indicating back drill on a drill chart, automatically, from an input say in the design of the pad stack, seems to be missing and would be nice to have. Right now we have to add all these notes about what layer not to breach and how deep is the hole (or conversely, what is the maximum remaining stub) by some special designation in the hole chart that points back to a sheet 1 note - having logic in the design tools to do this would be a plus. (author: Albee)    

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PCB Layer Introduction From Wonderful PCB Limited

PCB board layer analysis:

1.       Top Layer, also known as component Layer, is mainly used to place components, for than the laminates and sandwich plate can be used to wiring.

2.       Mid layer, can have up to 30, in a multilayer signal lines used for cloth.

3.       Bottom layer, also known as the welding layer, mainly used for wiring and welding, sometimes also can be placed components.

4.       Top overlayer, Projection of the contour is used to indicate components, components of symbols, nominal value or model and various kinds of comment character.

5.       Bottom overlayer, Same as the top silk layer effect, if various annotation on top silkscreen layer contain, so don't need to be at the bottom screen printing layer

6.       Internal planes, it is mainly used as the signal wiring layer, Protel DXP contains 16 internal layer

7.       Mechanical layers

8.       Solder mask layer, there are top solder mask and bottom solder mask. It is Protel PCB corresponds to the welding plate and the hole in the PCB file data automatically generated plate layer, laying resistance welding is mainly used in the paint. The board layer adopts negative film output, plate layer displayed on the bonding pad and a hole part represents not solder resist paint shop area on a circuit board, which is for welding parts.

9.       Past mask layer, there are top past mask and bottom past mask. When it is welding furnace used to correspond to the SMD components of solder joints, is also a negative form of output. Board layer to display on some representative circuit boards welding plate and the hole are not spread the area of solder paste, is can't to welding parts.

10.   Keep-out layer, it is mainly used for electrical drawing PCB border

11.   Multilayer, it is mainly used for layout multilayer circuits

12.   NC drill

13.   Drill drawing, it is used for setting drill profile.

Wonderful PCB circuit board factory production circuit board used in all kinds of electronic products, PCB type can be divided into: gold-plated board, heavy gold plate, tin plate. OSP antioxidant plate, tin plate, gold finger plate, plate, carbon oil LanJiao plate, high-frequency boards, aluminum circuit boards, etc. Products are widely used in computers, communication products, household electrical appliances. Product sales throughout the country China, receive the praise of users, welcome to inquire, to choose.  

PCB Design – How To Create Circuit Boards

To create a PCB Design you need to draw holes, pads and wires for your circuit. Then you send this drawing to a manufacturer or you etch it yourself.

 

Sounds hard? Don’t worry, there are many free tools out there that will help you do this.

 

Starting with schematics

 

Before you start drawing wires and stuff, you need to know what circuit you want to build. So you need to find or design schematics for your circuit. And you need a PCB design software. Then you are ready to begin the process.

 

Start by drawing your schematic diagram into the software you have chosen.

 

PCB design process

 

Preparing the board layout

 

Now it’s time to draw the board. You need to transfer your schematic diagram into a drawing of your printed circuit board.

 

Drawing PCB’s is artwork. Take your time, and make sure it looks good. Follow the design guidelines for drawing circuit boards.

 

Most PCB software will have tools that will help you draw your board from the schematic. I can’t cover them all, but I’ve written a PCB design tutorial for Eagle to help you learn.

 

Things To Think About

 

Will you put the circuit board in a box? Remember that tall components might need to be laid down flat to fit. With a drawing of your components placed on your board, print it out on a sheet of paper. Use this paper version of your board to test that it will fit the box and that your connectors will fit.

 

Getting your PCB manufactured

 

When you are done drawing your board, it is time to get your PCB design ready for manufacturing.

 

This basically means you need to check your board for errors and convert your board layout to Gerber files. Then, choose a cheap PCB manufacturer and get your board made.