What is Micro Sectioning on a PCB (Microsection)?

Some people know about sectioning on PCBs. However, this is not what it takes to be a PCB nerd at all. Do you know about micro-sectioning on a PCB? Not yet? Well, feel lucky since we are going to explain micro-sectioning right in this post for your today!

You define micro-sectioning as a much finer process than sectioning that takes place on congested and tight areas of PCBs. No, we are not going to let you go with this simple definition. There is more to micro-sectioning, and it needs your attention for your future projects as well. 

Role of Micro Sectioning on a PCB

The purpose of micro-sectioning is to exclude some layers and components of complex PCBs so that you can detect the faults in the layout, PCB parts, and their performance. Now these layers can be totally damaged as well. If you go for micrometer scale sectioning, you will be able to cover all the important aspects of solder joints and their robustness on PCBs, material composition, and, yes, plating thickness is also on the list. 

Uses of Micro Sectioning on a PCB

 Have you ever been interested in surgery? Or might you get a surgeon friend that cuts open humans in an operation theater? Well, consider micro-sectioning as the surgery of the PCBs. You cut open a PCB, perform micro-sectioning and see where the faults lie. Pretty similar to a normal human surgery, but let’s not go deeper into this analogy. There are some small steps that contribute to the success rate of this process. These are:

• Using a raw functional material of PCBs
• Perform build verification on the PCBs
• See if the width of hole-wall plating is suitable or not
• Whether all the conductors are of appropriate thickness or not
• Register all the paddings on the inside and outside of PCBs
• Develop connections between the PCB layers
• The surface finish of PCBs has a correct thickness, or not
• How thick is the solder mask 

· It’s time that we see how the PCB producers perform micro-sectioning at different intervals of PCB production. These include:

• Check the size and quality of the holes
• See if the registration is proper or not after drilling
• Verify the width of the wrap’s thickness and the barrel’s thickness after plating
• Check consistency, plating, roster, and problems that occur during the last stage, which is the quality assessment

Creating the Micro Sectioning on a PCB

Now your geeky brain must be wondering how PCB producers even create micro-section. There is no rocket science in it. Producers rely on special through-hole coupons for this purpose. Before doing this, they need to prepare the cross-sectional area of PCBs where they are going to perform the through-hole method. A process called automated coupon extraction is viable for CNC routing that assists in the extraction of the coupon. Other than this, there are some important factors that you need to know for the process:

• Precision router-cutter machines are important for the determination of PCB cross-sectional area through buried and blind holes.
• Also, the functions of these machines change as per their use for vendor qualification, failure analysis, conformance, and lot verification.
• Once you choose your purpose, you grab the coupon and cut a small piece of it for the sake of sampling.
• Now dip it in the resin or a soft acrylic if you have
• Wait for it, and it will harden itself to form a hockey puck-like structure.
• After this, you will crush this hockey puck structure and change it into a fine flat surface.
• Polish the surface, and etch it as well if there is a need.
• In the end, use a microscope to visualize and analyze the PCB.

Analyzing the Micro Sectioning on a PCB

There are different steps that you need to perform when analyzing your micro-section:

1. Build Checking: It means you are verifying the layers of complex PCBs through the process of micro-sectioning. It includes checking the width of cores, foils, prepregs, and also the connection between the solder joints. Not just this, build checking helps you verify if there are any cracks, thermal stress, delamination, gaps, and blistering on the layers. 
2. Wall Plating Thickness in PTH: The producers love to combine the through-hole method with micro-sectioning when analyzing. It helps you go deeper into the verification and quality check of PCBs. They use a coupon on every production panel they rely on. Six measurements are important to take, three per side of the hole. When you calculate the average of these six readings, you get the wall plating thickness. 
3. The thickness of Conductors: You already know that we don’t plate the internal layers of PCBs at all. It means you can use micro-sectioning to check the width of internal layers. Sometimes cleaning just removes some of the copper from the layers. However, you can still find some traces of copper left on the foils. It will help you determine the thickness. 
4. Hole Registration: When you analyze the micro-section by using a microscope, the internal padding is quite visible. Besides, you can also check the tolerance as well. A special coupon is important for this purpose, and you use it on all the panels. It helps you identify the position of the drilled holes in accordance with the layers. 
5. The connection between Layers: The PTH should be with a strong connection with the internal copper layers. When you perform micro-section analysis, it enables you to detect problems like insufficient hole-wall cleaning, which can lead to faulty drilling and weak connections. 
6. Surface Finish: You can even detect the surface finish of PCBs through micro-sectioning. Surface finish like lead-free HAL and hot air leveling support micro-sectioning. However, you can only measure the Nickel’s thickness through this if you want to determine for ENIG. Use X-rays for this purpose. 
7. Solder Mask: Sometimes, you need to measure the width of the solder mask, and micro sectioning just makes it happen for you. The standard thickness of the solder mask is always 8 micrometers. 

Micro Sectioning on a PCB for Traceability

If you have ever observed a coupon, there are some fine markings present on it. These markings help you identify the machine that produced it in the past. Now, this helps you in separating healthy PCBs from sick ones. Not just it, you can even reduce the chances of possible failures of PCBs through traceability. 

Identifying Failure with Micro Sectioning on a PCB Analysis

So the question is, how do you stop your PCBs from failing through micro-section analysis? We’ll see that in just a bit! 

• If your PCBs have faults and defects like improper solder mask thickness, poor etching, or defective registration, micro-sectioning can help you with it.
• The areas which are uneasy to reach out to, like pads, solder masks, and micro-sectioning, open a doorway for you to easily access these areas for analysis.
• Once you collect the data given by micro-section analysis, you can later use the same data for improving the PCBs
• You can rely on micro-sectioning for the failure analysis of PCBs as well when the internal failures keep hidden from the technicians.

Challenges of Micro Sectioning on a PCB

Let’s talk about the hurdles that you might face during micro-sectioning. Wait, did you think it was a smooth process? No, there are still some difficulties that you should take into your account. 

• The equipment and the materials used for producing a PCB can complicate micro-sectioning since these materials are unlike in hardness, and the equipment might be challenging to handle for the technicians.
• Sometimes problems with drilling can also occur.
• The positioning of the spot must be in the boundary of 10% of PCB, which leaves no margin of negligence at all. 
• In some cases, micro-sectioning can need you to use expensive equipment as per the complexity of your PCBs which can disturb your budget.

Additional PCB Testing’s for Micro Sectioning on a PCB

 Other than micro-sectioning, functional PCB testing also plays its role in ensuring the quality of PCBs. There are more tests that include: 

• Using X-rays to completely visualize the internal area of PCBs
• Test the PCBs for contamination that might lead to degradation and other problems like metallization.
• Check the frequency of the board to prevent breakdowns.
• Peel testing to determine how robust the laminate of PCBs
• Testing the solder float to check the thermal stress each hole can endure
• Flying probe testing is for checking the capacitance, inductance, and resistance issues of the PCBs
• Automated optical inspection of PCBs uses the latest 3D cameras to take pictures of PCBs and analyze them from their photographs.
• Burn-in testing is a rigorous procedure that you need to perform in the beginning; however, it can also harm the sensitive PCB parts.

Wrapping It Up

The bottom line is that micro-sectioning is becoming more important than ever since the PCBs are getting smaller for miniaturization. Since the process is crucial for quality checks, producers are training their employees for micro-sectioning as well. 

You also get a chance to diagnose the pain point of your PCBs through micro-sectioning. So, if you are facing problems like improper solder thickness, technical issues like lamination faults, and frequency changes, your PCB is in dire need of micro-sectioning. 

Hopefully, this discussion was helpful for you in terms of understanding micro-sectioning. We will see you in the next post with something more intriguing from the field of PCBs.