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What are PCB test Jigs, test Fixtures and how?

Any electronic project even if properly designed and built with utmost care is prone to bug and issues. It is very crucial to test the product or PCB thoroughly in early stages of design to ensure your projects going well. The testing can be done at PCB design level after using various design analysis techniques like EMI, Signal Integrity and Power Integrity ,the design issues can be minimized. But how do you test the PCB once bare- board PCB is in your hand or after components assembly has been done? How do you make sure that there are no shorts, open or bad solder joints? How to make sure current capacity, performance, component value and Impedance are within proper and expected tolerance level?

What are PCB Test Jigs

Also we should know and comprehend the common terms used in the Electronics hardware testing domain. Specialized and custom designed Test jigs and fixtures are used to test PCB. Test Point are identified and probed to identify the input to be given and output to be measured. A test jig can be identified as a device or machinery that holds a piece of machine work which now a days comprised of much electronic intelligence and guides the tools operating on it. It should not be confused with Test fixtures which are used to keep the object firmly in place. However, in PCB testing both the terms test jigs and test fixtures are interchangeably used as is meant as a electro-mechanical solution to test the printed circuit boards or PCB’s. Custom-made Test jigs and test fixtures are made as per the application of the board to test its test points.

The way of pcb testing

(1) Bare-board tests

Bare-board test are the tests done on unpopulated boards where defined circuit connection is verified properly on the fabricated board. A small voltage is applied and is verified at the appropriate points, a “short”, “open” are identified in these types of tests. Industrial CT scanning can show details of soldered path and connections by generating a 3D rendering of the board along with 2D image slices.

(2) Assembly Level Tests

After the board has been properly assembled it may be tested in a variety of ways using either manual inspection or using expensive Automatic test equipment (ATE).Automatic test equipment enables PCB test, and equipment test to be undertaken very swiftly. Automatic test equipment is quite expensive, and therefore it is necessary to select the proper type suitable for the application and board to be tested.

(3) Function tests

Functional test (FCT) is used as a final manufacturing step. It provides a pass/fail determination on finished PCBs before they are shipped. An FCT’s purpose in manufacturing is to validate that product hardware is free of defects that could, otherwise, adversely affect the product’s correct functioning in a system application.

In short, FCT verifies a PCB’s functionality and its behavior. It is important to emphasize that the requirements of a functional test, its development, and procedures vary widely from PCB to PCB and system to system.Functional testers typically interface to the PCB under test via its edge connector or a test-probe point. This testing simulates the final electrical environment in which the PCB will be used.The most common form of functional test, known as “hot mock-up” simply verifies that the PCB is functioning properly. More sophisticated functional tests involve cycling the PCB through an exhaustive range of operational tests.

Where to get your pcb project well done

PCBASTORE Supports a whole set of complete PCB test system (from initial circuit inspection to final function test) to keep your electronics projects going well.

Why Choose Multilayer PCB Stackup Planning

Planning the multilayer PCB stackup configuration is one of the most important aspects in achieving the best possible performance of a product. A poorly designed substrate, with inappropriately selected materials, can degrade the electrical performance of signal transmission increasing emissions and crosstalk and can also make the product more susceptible to external noise. These issues can cause intermittent operation due to timing glitches and interference dramatically reducing the products performance and long term reliability .The good thing to built right PCB substrate can effectively reduce electromagnetic emissions, crosstalk and improve the signal integrity providing a low inductance power distribution network. And, looking from a fabrication point of view, can also improved manufacturability of the product.

Suppressing the noise at the source rather than trying to elevate the problems once the product has been built makes sense. Having the project completed ‘Right First Time’ on time and to budget means that you cut costs by reducing the design cycle, have a shorter time to market and an extended product life cycle.Boards containing copper planes allow signals to be routed in either microstrip or stripline controlled impedance transmission line configurations creating much less radiation than the indiscriminate traces on a two layer board. The signals are tightly coupled to the planes (either ground or power) reducing crosstalk and improving signal integrity.

Planes, in multilayer PCB’s, provide significant reduction in radiated emission over two layer PCBs.  As a rule of thumb, a four layer board will produce 15 dB less radiation than a two layer board .

What should we consider when selecting a multilayer stackup ?  • A signal layer should always be adjacent to a plane. This limits the number of signal  layers embedded between planes to two and top and bottom (outer) layers to one signal.  • Signal layers should be tightly coupled (<10 MIL) to their adjacent planes  • A power plane (as well as a ground) can be used for the return path of the signal. • Determine the return path of the signals (which plane will be used). Fast rise time  signals take the path of least inductance which is normally the closest plane. • Cost (the boss’s most important design parameter).

Do you want to know more ?

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How to design HDI PCB?

Accompany the consumer electronic products developing, people are pursuing for more small and clever products for easy carrying.This cause the engineer must use more small PCB size to finish the product design, so Multi layer HDI PCB board will be a trend for future

PCB industry. For engineers,must know some design rules of HDI PCB and production capacity from different PCB factory, here I suggested PCBA STORE for you easy and quick to get HDI board cost.

And Below is some basic rules and knowledge about HDI PCB for your checking:

About Vias

Vias are small holes drilled into PCB layers in order to create connections between components and the layers of the board. Depending on the type of via, the via may be made with a mechanical drill or a laser drill. Mechanical drills are used for larger vias and laser drills are used to make microvias. Vias can be filled with copper, epoxy or metal epoxy. Copper is the most commonly used via fill. Epoxy is non-conductive and will insulate from signals and heat. Metal epoxy is conductive and may be used to spread heat. If the via is too long and narrow, or is filled improperly, voids and other inconsistencies that impact board performance can occur.

There are three main types of vias: through hole, via-in-pad, and microvias.

About Through Hole Vias

Through hole vias go all the way through  a printed circuit board. Through holes are mechanically drilled and are typically 8 mil in size, though Sierra Circuits can go down to 5.9 mil through holes. These vias are usually plated with copper, but they can also remain unplated, called non-plated through holes.

Through holes allow component wires to go into the hole to be connected to the board. Through Hole ViasExample of a through-hole via. To specify through hole sizes, state the size it should be with a range that the hole can be plated down to. For example, the hole needs to be 8 mil in diameter. If the acceptable range of the via is 5 mil to 11 mil, then the specification will be 8 mil +/- 3 mil.

About Via-In-Pad

Vias-in-pad are mechanically or laser drilled into the board, filled, and plated with a pad over the top. The component can then be set on top of the pad with solder and connected to other layers through the via. This save space on the board since the component and pads are stacked on top of each other. In regular through hole, the pads and vias are spread out and take up more real estate. Without a plated via, the solder would melt into the via.

About Microvias

Microvias are defined as any hole equal to or less than 150 microns in size. Microvias are used in HDI boards because they are much smaller than mechanically drilled through holes. The hole connects the layers with copper plating. These are drilled into the board as cone shapes so the sides of the via can be easily and properly plated with copper. The hole can only go from one layer to an adjacent layer, so vias that need to go through multiple layers are stacked on top of each other or staggered in the board.

About Stacked and Staggered Microvias

Stacked microvias are laser drilled vias created one at a time and sequentially stacked on top of one another. Two microvias stacked on top of one another is the most common, but up to four vias can be stacked. Four stacked vias is typically not recommended due to higher cost. Staggered microvias are microvias that are set up like a staircase, one diagonally below or above another.

About Buried and Blind Microvias

Microvias can be buried or blind. Blind vias are vias that enter through the outer layer of the circuit board and end in one of the inner layers; the via does not go all the way through the board. Using blind vias increases wiring density. When signal tracks from an outer layer need to be routed to an inner layer, blind vias can be the shortest distance and thus best way to do this. Some microvias go through two layers, called skip vias, but this can cause problems with plating, and so is advised against.

Microvia Design Guidelines

Hole size

When determining hole size, keep aspect ratio in mind. This will ensure your vias can be properly plated and will not encounter any issues. Consult with your PCB manufacturer if you would like them to look over your design.

Pad size

The size of the pads need to be minimized to reduce cost, but keep in mind the possibility of an annular breakout if the pad is too small, and the impact it would have on yield of your HDI boards.

Aspect Ratio

Aspect ratio is the thickness of the PCB dielectric material divided by the diameter of the via. Vias need to be a manageable size to be properly plated. If holes are very small and the board is too thick, plating the via will be an issue and the metal may not make it all the way through the via. Imagine trying to drink a thick milkshake through a very thin straw. Like the milkshake, plating material would have a hard time plating a very thin but deep hole.

Hope above information will helpful for you to finish the HDI PCB design!

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