There is a need for printed circuit boards (PCBs) to be electrically tested in line with the Guidelines & requirements of the IPC-9252 for the electrical testing of the unpopulated printed boards. However, how do we test these boards?
Before we go to the different types of PCB electrical testing and why it is important, let us consider what a printed circuit board is and its composition.
What are Printed Circuit Boards (PCBs)?
Printed circuit boards (PCBs) are known as the most frequently used name. However, we can also refer to it as the PWBs as well as printed wiring cards. Before PCB came to be, the constriction of the circuits were done via point-to-point wiring, which is laborious. This resulted in short circuits, as well as frequent failures at the wire junctions when the wire insulation started to crack and age.
When wire wrapping came to be, there was a significant advancement. This involves the wrapping of a small gauge wire around a specific post at every connection point. Furthermore, this creates a kind of gas-tight connection that is very durable and can be changed with ease.
When electronics began to move from the relays and vacuum tubes to the integrated and silicon circuits, the cost and size of the electronic components started decreasing.
Composition of Printed Circuit Boards
There are different materials that are laminated with adhesive and heat to become one object. Let’s consider them.
FR4
This substrate or base material is fiberglass in most cases. Historically, FR4 is the most used designator for fiberglass. Thus a strong and solid core is what gives the PCB its common thickness and rigidity.
Copper layer
This is the next layer – thin copper foil. This has copper traces which are laminated onto the board with adhesive and heat. When we talk of a 2 layer or double sided board, we mean it has two copper layers. The copper thickness could vary and its weight usually specifies it.
Solder mask
The solder mask layer is that layer present on the top of your copper foil. It is this layer that gives the green color or any other possible color. The solder paste is also important here.
Silkscreen
This whitish later is usually applied on the top of your soldermask layer. It adds symbols, numbers, and letter onto the PCB. This ensures easier assembly. It also helps humans to have a good understanding of the board.
What are the Types of PCB Electrical Testing?
No exact test is necessary for PCB electrical testing, so far the tests that have been conducted prove that the printed circuit board meets the standard of electrical testing. The procedures for electrical testing for the printed circuit boards or printed wiring boards may include the following:
Resistance Testing
This simultaneous testing type is a very reliable method that helps in measuring the resistance value in ohms. Furthermore, the resistance measures the collisions, which occur between the atoms and electrons, which can disturb the electron flow whenever the current flows via the conductor. When you test for resistance, then you are searching for a low resistance to indicate a very good conductor.
Also, circuits that feature more resistance, the thinner and longer they are. This is a very important consideration that you must take note of when testing.
Capacitance Testing
Capacitance testing is another simultaneous testing type that searches for shorts present in the circuit board. This process deals with using electricity to charge a net. Then the next step is to measure this induced capacity.
Continuity Testing
Continuity testing is a very reliable method that makes sure that the resistance present in-between the test points doesn’t surpass or exceed the necessary or required limits.
Comparative Testing
Comparative testing is usually done making use of a master board, which you’ve verified already to help in teaching a list program. With this, you will end up comparing the other boards against. Now, thus pcb electrical testing type has one issue. A possibility exists that the master board once had a defect.
Clamshell Testing
Testing the two sides of a circuit board simultaneously are conducted once. It is a popular method that aids reliability. This is because you will be testing all the points present on the circuit board at once.
Flip Testing
For flip testing, you perform this on any of the sides of the printed circuit boards, taking this as the universal grid. In contrast to the clamshell testing, this testing is less accurate.
Adjacency Test
Here,Adjacency test helps in checking the isolation present between the conductors
Adjacency Testing
This involves testing shorts. You conduct this by checking the isolation that is present in-between the conductors. Here, you may test the proximity adjacency or the line-of-sight adjacency.
Flying Probe Testing
The flying probe test is a very reliable testing method. This deals with using a flying probe test sequence. Also, this flying probe test sequence probes high speed boards searching for openings and shorts all through the board.
How an Electrical Test Confirms the Integrity of a Printed Circuit Board (PCB)
As the technology of printed circuit boards has been inclining steadily for many years, one major focus has been on the other things that this part can offer. Decrease the circuit widths, include additional layers, control its impedance, add additional components, blind vias, buried vias – it is a lengthy list of technology changes.
As PCB manufacturers, we see the completed design set to go into production. However, is this the case? Most times, we take a look at the received data production of a customer, and then we ask ourselves if this part could be produced.
Furthermore, we push the limits of the materials and testing equipment, tweak that process so as to increase and improve the yield, as well as celebrate these successes. However, in what ways has this had an impact on production’s testing portion?
The idea of bare board testing, which was optional has now become something of the past. It is no longer realistic to inspect visually in process as well as perform an AQL (acceptable quality) and sure that that specific part is good and okay.
However, have we taken a look at the process of testing? The PCB designers can have an impact on lead time, so as to process largely with the technology-driven printed circuit boards (PCBs). When the components, holes, and layers are more, then the longer it will take the lead time in processing it. Also, it will also take a longer time to test points in the eventual or end product. But how?
In this section, we will consider the well known circuit board testing types. Then we will also take a look at its impact on the integrity of the printed circuit boards (PCBs).
Why the DFM Review is Significant to a PCB Electrical Testing
The integrity of the electrical test begins with a very good design, NETLIST data, as well as a clean data set that comes in an ODB++ format or RS274X – X2 format. The testing product begins in CAM with the design for the manufacturing review. Also, quality data including netlist will help in improving the entire process.
PCB testing begins in CAM. The engineering performs one major set up as well as design review. This has to do with checking the layers to see if anything is less than the standard. Also, when the NETLIST is give, we just compare all the files present in them. This test is your first of all tests of the final end-product. During engineering, it will repeat the process all through the CAMing process of the project.
However, what if the NETLIST is absent? You will be surprised to hear that this is common. In fact, it is very common that the NETLIST isn’t given. What manufacturers do most times, is to ask the customer if they have a NETLIST and most times, they don’t.
This is where the manufacturer uses their software in extracting a NETLIST from their database. This tool is a great one. However, it is only great as the data supplied. When an error is built inside the files and it is absent in the DFM, then this part will not process correctly.
Why is it Important to Test Circuit Boards?
Most customers ask if the manufacturer tests the printed circuit boards or conduct a complete 100% test. This is very important and all pcb manufacturers must do this. All your orders must be electrically tested, as well as its technologies. There are customers that still don’t believe that the manufacturer has done the testing and still require some parts tested again.
Processing the technology or high technology printed circuit boards isn’t exact science that should be performed just by robots or machines in the majority of factory settings. The handling of materials, human error chemistries, and testing equipment failures, can affect the processing, as well as lead to failures in all the circuitry layers.
Conclusion
RayMing PCB and Assembly supply printed circuit boards, which are well tested for accuracy and quality by dedicated and skilled professionals using top-grade testing equipment. If you wish to learn more and understand how we supply our high-quality PCBs globally, please contact us today.
