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What are types of PCB test points, its uses, and design guidelines?

By Mer-Mar Electronics | Date posted: | Last updated: February 28, 2023
PCB Test Points

With the PCB being a crucial component of an electronic appliance, it is extremely important to verify the PCBs function during its development. This is a job that it done with the help of test points. PCB test point ensures that you can improve processes involved in the various stages of production.

What are PCB test points?

A PCB test point is a small wire loop through which you can inject test signals and monitor the board’s circuitry. The output of the test signal as compared to the desired results will help you make any optimal changes. Typically, these PCB test points need to be located on the outer layer of the board. The test probe tips can be of various shapes to cater to different testing surfaces.

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Types of circuit board test points

PCB Test points are usually of the following types:

1. Probe PCB Test Point

This is an accessible point that can be accessed with a handheld device. It comes handy to conduct surface level testing, for instance to do with current supply and ground values.

2. Automated PCB Test Points

As its name suggests, this is used for automated test equipment. These automated test points include vias, through-hole pins, metal landing pads, and more. In turn automated testing is of 3 types:

I. Bare board testing

This is undertaken before components are assembled. The prime purpose of this is to ensure that electrical conductivity on the board is consistent.

II. In-circuit Testing (ICT)

In circuit testing reveals if all the components on the board are working flawlessly.

III. Flying Probe Testing (FPT)

This test comes in extremely handy to detect issues such as:

  • Shorts
  • Opens
  • Resistance Values
  • Component Orientation, and more.

List of signal which should have test points

The following signals benefit from having test points:

  • Power supply rails
  • Ground
  • Programming connections
  • JTAG ports
  • Serial communications busses
  • Reset lines
  • UARTs
  • Programmable references
  • Interrupt lines

How to use test points on PCB?

For a PCB test point to work well, it is important that the point should be an exposed metal spot on the outer layer of the board. That way, the probes of the test equipment will make contact with it. The designer can then designate thru-hole pins & vias as test points.

Next up, it is important to identify the right locations as test points. The PCB design software tool will allow you to do this basis the requirements or parameters you set up.

Once this is done, the information can be exported into a test point file. With the right PCB design system test point generation is easy. Additionally, there are several other features that will enhance quality.

Advantages of adding test points to your PCB

The major advantages that come from adding test points to the PCB include:

  • Their profile is similar to that of surface mount components hence they fit well and are versatile.
  • Since they help identify issues in the early phases of design, they ensure that there aren’t costly errors to pay for in the later stages.
  • They ensure easy error detection without compromising on the PCB design.

PCB Test Point Guidelines

When it comes to proper test point placement, the following PCB test point guidelines need to be kept in mind:

  • All test points should be placed on the same side of the board.
  • To ensure testing efficacy, the minimum test point distance needs to be 0.100 inches.
  • Uniform distribution of test points is ideal.
  • Keeping all tall components in a designated area will ensure the access to test points isn’t blocked.
  • It is important to keep manufacturing tolerances in mind while accommodating test points and probes.

To sum up

Adding test points to the PCB help with easy error detection and leads to huge savings in terms of time and cost. While test points are essential in verifying the integrity of a PCB, the various guidelines need to be kept in mind in implementing them. For instance, limiting the test points on a PCB board go a long way in ensuring that there are no chances of accidental shorts & therefore damage to the circuit.

To avoid such future problems and to save time and money hiring Mermar Electronics is the best decision. Mermar Electronics provides PCB assembly, PCB fabrication, and PCB design services under one roof. Fill out form below to request a free quote or send mail at sales@mermarinc.com

PCB Test Point FAQs

1. How big should a test point be?

Larger test points work well as it makes it easier for the probe tips. Ideally a 0.050-inch test point works well.

2. How do you know if your PCB is shorted?

There are several indicators of a short. You could witness visual damage such as a cracked IC, blown capacitor or more. There could also be an acrid smell.

3. How do you choose a PCB test point?

The guidelines to follow when it comes to choosing a test point include placing test points on the same side of the PCB, distributing them evenly, and having a minimum distance of 0.100 inches between them.

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PCB Test Points

Explore the types of Vias in PCB and the process to make it precise!

By Mer-Mar Electronics | Date posted: | Last updated: March 7, 2023
PCB Via

When it comes to multilayered PCBs, their interconnection has a strong role to play in their efficacy. It is here that a PCB via comes into play. They are used to electrically as well as thermally connect the traces, pads & polygons on the different layers of the PCB. With the miniaturization of SMD chips & the rise of high-density BGAs, the role of vias is only increasing. Let us look at the different aspects of a via in some detail.

What does a PCB Via consist of?

Broadly there are 3 parts to a via. These are:

1. Barrel

This is the conductive tube that fills the drilled hole.

2. Pad

It connects the end of the barrel to the component, plane or trace.

3. Antipad

This is the clearance hole between the barrel and the no-connect metal layer.

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Different types of Vias in PCB

PCB Vias can take the following different forms:

1. Through-hole PCB via

This is a commonly used via. In such a via, the holes are drilled through the various layers of the board. Such vias are easy to make and they consume a lot of space on the board.

2. Buried PCB via

This via connects internal layers of the board. It is of great use in miniature appliances where component density is high.

3. Blind PCB via

This via starts on either the top or bottom of the board but doesn’t go to the internal layers. Needless to mention that drilling a blind via PCB requires a lot of dexterity.

4. Microvia

These connect the adjacent layers of the board and are under 150 microns. These are put to efficient use in high density interconnect boards. Micro vias in PCB consume a lot less space.

The kind of via to be used depends on several factors including but not limited to:

  • Technology used
  • Needs of the circuitry
  • Cost of fabrication

What is Via in Pad?

Simply put, it is a design practice that involves placing a via in the copper landing pad of a component. The big advantage of via in pad is that it allows high component density and supports miniaturization. While with traditional vias, the signal is routed away from the pad and then to the via, in case of a via in pad, the drill hole for the via is inside the pad. Therefore, it reduces the space taken up by trace routing & helps in miniaturizing the PCB.

PCB Via in pad is particularly convenient when it comes to routing as the signals do not stand the risk of going outside the device’s footprint.

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Creating Precise Vias in Pad

Some guidelines to create precise via in pad include:

  • Use small via diameters.
  • Ensure that when it comes to component placement as well as via capping or filling, you follow the recommendations laid by the component manufacturer.
  • The non-component side needs to be capped with solder mask.
  • Vias shouldn’t be kept open as the inner copper tends to oxidize, which can, in turn, impact the lifespan of the PCB.

Advantages of Via in Pad

PCB Via in pads offer a number of advantages such as:

  • They promote space saving & lend themselves to high density of components.
  • They help in thermal dissipation.
  • Offer lower inductance on account of no dog-bone pads with traces.
  • Increase voltage capacity of the via.

When to Use Vias?

Via in pad finds extensive use when small pitch components are in use. Additionally, when routing complex BGA & LGA packages capped via in pad can make the process simple. They help in minimizing parasitic inductance as well as EMF emissions in the case of high-frequency designs. Via in thermal pads is also useful in heat management.

Reason behind PCB Via failure

Typically, failure of vias occurs on account of the differential expansion and contraction when it comes to the copper plating & the PCB in the out of plane direction. On account of the differential expansion and contraction, there is cyclic fatigue in the copper plating that can lead to cracks. It is imperative to follow the IPC guidelines for vias. The IPC 4761 defines the various via types from type I to type VII. While type one defines tented vias, type VII defines filled and capped vias which are filled with non-conductive paste and are over plated on both sides.

Guidelines for Vias

Some guidelines to create precise via in pad include:

  • Use small via diameters
  • Ensure that when it comes to component placement as well as via capping or filling, you follow the recommendations laid by the component manufacturer.
  • The non-component side needs to be capped with solder mask.
  • Vias shouldn’t be kept open as the inner copper tends to oxidize, which can, in turn, impact the lifespan of the PCB.

To sum up

PCB vias are extremely crucial in multi-layered circuit boards. For board components that bear power or quick signals, you would need several vias to link the layers. The use of multiple vias as opposed to a single large via helps keep inductance in-check and works well in case one of the vias tends to fail.

Mermar Electronics thoroughly evaluate the PCB via requirements and deliver a high-quality product with a quick turnaround time. Mermar Electronics also provides PCB design and PCB assembly services. To request a free quote, fill out the form below. You can also send mail at sales@mermarinc.com.

PCB Via FAQs

1. Why fill PCB vias with epoxy?

Non-conductive epoxy helps in that it ensures that the board expands or contracts in conjunction with the laminate material & so there are reduced chances of any fractures caused on account of stress. Conductive epoxy helps with transferring thermal energy and hence conducts heat away from the board.

2. Do vias increase the cost of a PCB?

While the use of vias, particularly the use of micro vias add to the cost of the PCB, importantly they help in keeping the PCB size small and component density high.

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What is the importance of PCB silkscreen and solder mask in PCB design and prototyping?

By Mer-Mar Electronics | Date posted: | Last updated: September 19, 2022
Solder Mask vs Silkscreen

When it comes to PCB design and eventual prototyping, two aspects that are very important, but may not get the discussion they deserve are Solder Mask & PCB silkscreen. Let us look at the difference between solder masks and silkscreen and each of them in detail.

Silkscreen VS Solder Mask

What is solder mask in PCB?

Also referred to as a solder resist, a solder mask is a thin polymer. When applied to the surface of the PCB it helps seal the copper from environmental conditions. Essentially a solder mask performs two essential tasks. First, it helps prevent oxidation & second it ensures that solder bridges are not formed. If oxidation does happen it impacts the electrical property of copper. In turn, this affects the functioning of the PCB.

A solder bridge refers to an electrical connection between two conductors. When a solder mask is used it prevents this from occurring. A solder mask becomes particularly important for mass-produced boards where the soldering is done automatically by way of reflow or wave solder techniques.

A solder mask is available in a wide variety of colors. Additionally, it also comes in different media ranging from epoxy liquid to liquid photo imageable solder mask inks as well as dry film photo imageable solder masks. LPSM can be either sprayed on the PCB or silkscreened. When it comes to DFSM, it is typically vacuum laminated on the PCB followed by developing it.

Function of Solder Mask in PCB Design

To sum up, the functions of a solder mask layer include:

  • Ensuring that the conductor circuit doesn’t break physically.
  • Ensuring that there is no short circuit from the bridge connection during the process of soldering.
  • Ensuring that oxidation doesn’t happen on the copper layer.
  • Ensuring that there is no short circuit between conductive lines and solder joints.

Silkscreen

While a silkscreen is often seen as a not so important layer at first glance since it does not impact the electrical functionality of a PCB, the fact remains that it provides valuable information that can make or break the functioning of the PCB.

A silkscreen in PCB is typically used to transmit the following information:

  • It states the location of the parts with the use of reference designators.
  • It helps identify test points.
  • It offers identification numbers unique to each board.
  • It offers warning symbols.
  • Ensures polarity of parts.

When a PCB is being assembled, the information provided by the silkscreen is invaluable as among other things, it ensures that the components are correctly placed. In cases where a silkscreen is not available an assembly drawing becomes imperative.

The silkscreen also plays an important role in PCB testing as it provides the engineer with the location where measurements are to be taken, during the process of testing. This can go a long way in finding out the causes of potential failure. Some of the markings of the silkscreen used for testing include:

  • Test points – These indicate the location on the board where the desired values are known.
  • Warning symbols – These warning markings come in handy as they indicate areas such as a high voltage point.
  • Part numbers – In case a datasheet is not present it provides device information.

How silkscreen applied on PCB?

A silkscreen is applied on the PCB in three ways:

  • Manual Screen Printing (MSP)
  • Liquid Photo Imaging (LPI)
  • Direct Legend Printing (DLP)

How to ensure accuracy of silkscreen?

The importance of a silkscreen in ensuring PCB accuracy is undisputed. What is important is that the silkscreen should be accurate. Some tips to be followed that ensure accuracy of a silkscreen include:

  • Using fonts that work for the PCB contract manufacturer.
  • Using colors that are readable.
  • Following the dimension guidelines so that the silkscreen is not covered by components.

To sum up, both solder masks & PCB silkscreens play important roles in ensuring that the functioning of the PCB isn’t affected, albeit in different ways.

To get quality-based PCB design and manufacturing, contact us at sales@mermarinc.com or call us at (760) 244-6149. We provide PCB manufacturing services with a quick turnaround time. You can fill out the form below to initiate your PCB prototyping and PCB designing according to your requirement.

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Top PCB layout tips and tricks to relieve the swelling of post-assembly rework

By Mer-Mar Electronics | Date posted: | Last updated: November 25, 2022
PCB Layout Tips

Once the PCB components are placed on the board and routed, any requirement that calls for a sizeable amount of rework, can prove to be extremely cumbersome. Not only does it take time that in turn impacts go-to-market and impacts your competitive advantage, it also comes at a cost. Additionally, if your board hasn’t been designed to support rework, it makes the job even more difficult. In such cases, rework can also impact other sensitive parts in the vicinity and lead to further complications.

Fortunately, there are some handy PCB layout tips and tricks, which if followed, can go a long way in reducing the amount of rework required.

Before we look at these tips, it will be worthwhile to examine what are some of the PCB rework issues that are typically encountered:

Typical PCB Rework Issues

Part Replacement – Sometimes a wrong part may have been initially specified. A seemingly small lapse, it leads to wasted time, effort and costs.

Defects in Assembly – A big part of the rework is required when parts haven’t been soldered correctly during assembly. Sometimes these PCB soldering issues can be on account of improper DFM clearances or incorrect component locations.

Inaccessible Parts – Sometimes it is hard to replace parts or rework them, on account of the fact that the parts are either too close to other parts or sometimes even hidden. If the part is positioned in a manner that tools cannot reach them, it can be a big issue that can impact rework.

Damage – Parts that are placed very close to the components that need rework can also be damaged. The damage can happen on account of heat of soldering reaching these parts or any physical damage while replacing other parts. The rework process therefore may lead to reworking on these collateral damages too.

Needless to mention that rework also becomes a deterrent when you are chasing a deadline and also trying to keep things under budget.

PCB layout Tips to reduce post assembly rework

Here are top handy layout tips that when implemented well can go a long way in avoiding or minimizing rework issues:

  • Accurate BOM – Now this is a gold standard when it comes to avoiding rework. Sometimes the part information in the design isn’t updated or the schematic isn’t synchronized with the layout. In turn, it leads to reworking incorrect parts. It is imperative, therefore, that the BOM is totally in sync with the PCB design and layout.

  • DFM guidelines – A lot of the rework related to parts being placed in the wrong location or parts not soldered correctly can be avoided if the DFM guidelines are clearly specified and are followed accurately.

  • Room for rework – High density of parts is a function of miniaturization of devices. The components also need to be placed tightly together to ensure signal integrity. However given these constraints it is important to allow some room for rework. The PCB contract manufacturer will be in the best position to offer recommendations to be able to incorporate room for rework within the constraints.

The need to choose the right PCB contract manufacturer

As the complexity of a printed circuit board increases, so does the potential for rework. The right contract manufacturer given his expertise and access to industry best practices will be able to minimize the potential of rework. That said, even with all the precautions there will be some PCB assembly defects that can occur which an experienced PCB manufacturer will be able to cater to.

While potential rework situations need to be taken into account, what also need to be planned for are aspects such as:

  • Some printed circuit boards need additional testing.
  • Sensitive components need room for access. This may include additional vias for probing or header pins for test access.

An experienced and skilled PCB contract manufacturer can easily identify areas of the board that may need more room for rework or for extensive testing. Besides, a skilled PCB contract manufacturer will also have the engineering prowess that will be of utmost importance when it comes to meticulous rework in the least amount of time and with minimal added costs.

At Mermar Electronics, we have 4 decades of solid experience in assembling printed circuit boards, PCB design and PCB assembly rework and repair service through innovative tools and technologies. If you have any requirements or inquiries related to PCB manufacturing, Get a quick quote, or simply drop an inquiry at sales@mermarinc.com

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