What do you need to Know about Tolerances on Printed Circuit Boards?

The PCB production process completely relies on tolerances. You cannot afford any negligence when it comes to setting the PCB tolerance. Now, what exactly is PCB tolerance, and why they are important for this particular process? We are going to address all your questions in this post so that you can play with PCB tolerances like a pro.

If you are into PCBs, you must be aware that different factors influence PCBs. Due to this reason, we need to pay attention to the tolerances as well. One major benefit of tolerances is you can have quick access to the PCBs from any producer. Now, here’s the twist. Sometimes you will see producers use intense tolerances, which are not recommendable if you are tight on the budget. It also extends the production process, which can be a nuisance for some producers. 

Importance of Tolerances on Printed Circuit Board and PCB Design 

There are different producers out there who specialize in different types of PCBs. From simple to complex, single-layer to multi-layer PCBs, these producers can handle different PCBs for you. However, you might still don’t be fully satisfied with their performance. But we are here to save you from this fuss. Our experts realize this and carefully play with the PCB tolerances for your sake. We are going to discuss what factors influence PCB tolerances. So let’s get into it! 

1. Materials: If you don’t want to compromise on the PCB materials, then you need to leave this to us. Since we use DuPont and high-speed Pyralux TK. You can also rely on our Isola FR406, FR408, polyamide, and much more. Now can you get this wide range of options from other producers? It’s your call to decide! 
2. Thickness: Our experts know that the width of the material matters a lot in this process. Therefore, it depends on the type of PCB we are producing. However, the recommended width that we normally work on is +/- 10%, but it can vary as per the PCB type. 
3. Maximum bow & twist: The bow and twists differ in numbers when it comes to SMD PCBs and NON-SMD PCBs. It is important to insert an accurate amount of twists and bows for efficient performance. 
4. Copper Thickness: The efficiency of a PCB in terms of current relates to the copper thickness. We always measure the copper before using it in production. So that there will be no chance of mishaps. Now, let’s see how different copper thicknesses have different applications: 
5. 0.5 Oz Copper: Such a thickness is useful for cheap quality PCBs. You will use this copper for the inner layers. However, using it externally is not recommendable. 
6. 1 Oz Copper: For the next layer, you need to go for the accurate copper thickness and for this, 1 Oz is suitable. 
7. 2 Oz Copper: While working on the next layer, you can use the weight of about 2 Oz which is the optimum weight for this purpose. As far as Rigiflex is concerned, we keep our range from 0.5Oz-6.0Oz depending on the type of PCBs we are working on. 
8. Hole Sizes: A PCB design might consist of three types of holes in general. You call these holes plated holes, non-plated holes, and vias. Now the size of these holes will determine the tolerance. 

 You can trust RayPCB with the following types of holes for your upcoming PCB designs: 

• Minimum drill: The minimum drill hole differs for the simple and flex PCBs. Therefore our experts precisely work with the flexible PCBs and keep the holes up to .008″ (0.2 mm), and for rigid-flex PCBs, we keep the size of the holes up to .006″ (0.15 mm). 
  • Laser Size: The minimum micro via size also matters for the perfect PCBs. These are different in size for all the PCB types. If the PCBs are rigid, they must be maintained at three mils (0.07 mm). For the flexible PCBs, it is also three mils (0.07 mm), and for rigid-flex PCBs, the recommended size is one mil (0.025 mm).
  • Minimum Via Laser Size: The minimum via laser size can make or break your PCB designs. It means you need to keep the size up to 5 mils (0.15 mm) if you are developing flexible PCBs and one mil (0.025 mm) if your PCBs are rigid in nature. 

• PCB Board Thickness: The width of the board itself is important to consider. So that the PCBs can perform efficiently in the long run. Problems occur when we don’t consider the accurate widths of the PCBs. If your board is flimsy or thin, it will undergo damage. Thick boards are much stronger and more durable in nature. We at Rigiflex produce flexible and rigid-flex PCBs for you of widths 0.5mm to 3.0mm (0.02″–0.12″). Don’t worry if you want a rigid PCB from us. We produce rigid PCBs that have a width of 0.2 – 5.0mm (Max) as well. 

How Do Tolerances on Printed Circuit Boards Impact the Production Yield Rate?

The yield rate means the amount of PCBs we are producing. It can include different factors like prototypes and the volume of production. Low-volume production of PCBs comes in handy when you need to deliver them to the domains of medical and aerospace. However, low and high volumes do not mean you will not inspect and test your PCBs. Defective PCBs cannot only tarnish your reputation. They can lead to major complications that we are going to discuss below:

• Faulty PCBs complicate the process of fabrication, leading to abrasion, delamination, and dents in the PCBs
• Current leakage due to deformed PCBs can cause fatal damage to the users.
• PCBs containing even a little moisture can start rusting of the board as well, and if this is the problem with your PCBs, immediately use moisture protection techniques to prevent further damage.

What we mean by the yield rate is the total amount of PCBs we produce. But these PCBs should be of industrial grade so that the users can use them. It does not include the faulty PCBs at all. You need to repair them before sending them to the customers. Now, some types, like PCBAs, need you to re-design the PCBs from scratch. It can lead to an increase in the overall production cost. 

How Can Tolerances on Printed Circuit Boards Improve the Yield Rate?

Did you know that PCB tolerances can help improve the yield rate? But for this, you need to pay attention to the type of fabrication and PCB assembly as well. These both factors can highly enhance the PCB quality, making them industrial-grade for the users. Therefore, for developing highly useful PCBs, you need to test different ranges of tolerances. In this case, DFM tolerances are recommendable. For this reason, PCB producers rely on different types of special tools for producing PCBs.

If you go for drilling the holes, then only a small thickness will work for you when you’re considering vias. The largest bore width means that the process will be extensive for working the same vias. Now, this depends on your PCBs and their type, and in some cases, applications of PCBs determine this as well. We dont recommend looking for extreme methods since these can increase the production cost. It also enhances the budget, and risks get more prominent than ever.

To save yourself from all this hustle, you need to rely on the PCB tolerances that fit best with your PCB designs. So that there will be fewer chances of risks and the PCBs will become more efficient in performance. At the same time, you will be able to manage the desired yield rate and achieve your goals by ruling out as few defective PCBs as possible. 

Issues with Using the Incorrect Tolerances on Printed Circuit Board 

By far, you know PCB tolerance is important to make the entire PCB production of PCBs seamless, plus enhancing their efficiency. But in case of ignoring the accurate PCB tolerances, you will end up facing problematic fabrication, assembly, and performance. Due to this reason, we are going to take a deep look at these problems below: 

·       Fabrication

Let’s assume that you are using a small width for fabrication. Now, what will be the result? It will cause problems! Due to the small width, you might be etching the metal more than needed. If the trace is too thin, it will allow you to exclude a whole chunk of metal. For instance, we cannot use a 3 mil trace for seamless fabrication because it is too thin and will cause extra etching, which is needless. Now bigger traces will also cause the over-etching. In both cases, the PCB fabrication suffers. Therefore, the technicians who perform the fabrication need to use accurate trace widths for this purpose. If you are not doing the etching properly, it will also cause defects in the process. Sometimes when we use small trace widths, the current carrying capacity also gets disturbed. If you need them to carry more current, then thinner traces are not recommendable. 

·       Performance

Inaccurate traces directly impact the electrical performance of PCBs, which clearly means we dont have any margin for faults here. After all, the performance of PCBs is what matters at the end of the day. Or else there is no point in producing them in the first place. When you are dealing with controlled impedance, you need to use calculated traces so that these will not interfere with the natural performance of the ground plane. Also, inaccurate traces disturb the signal integrity of the PCBs, which also reduces the efficiency in performance. If the trace is thin, it will damage the loads and might even burn them as well, which means the ultimate failure of PCBs. You need to insert the right track in the construction of PCBs so that there will be enough room for air to ventilate through the setup to avoid damage caused by overheating. 

·       Assembly

Trace widths also influence the PCB assembly. If the trace is too large, it will damage the ground plane, which will lead to heat skinking and disturbed solder joints. It also causes tombstoning, in which the SMD parts stack up on the boundary of PCBs. All in all, inaccurate sizes of traces create problems when you are soldering the PCB parts as well. You can even properly inspect such PCBs because the traces you have used are totally not suitable. It means it might make it hard for the users to rely on them in the long run. 

Now you know using inaccurate traces means PROBLEMS! But is there any way you can save your PCBs from them? Of course! We call it trace width routing. However, you still need some effective tips while routing the trace widths to avoid problems in the assembly, fabrication, and performance of PCBs. 

Recommendations for Tolerances on Printed Circuit Board 

• It is better to inquire about the skills of the PCB fabrication firm that you are hiring. How much have they experienced in PCB fabrication? Can they handle all types of trace widths for your PCBs? Once you are satisfied, you can proceed with your fabricator. 
• You need to talk to your fabricator when it comes to using the trace widths. They should not use the regular three mil trace, which complicates the process. However, if you are ordering BGA PCBs, then you can allow them to use such traces since these are helpful in short-distance routing. Other than this case, we use a five mil trace width for PCBs. 
• If they are using longer trace width, then the accurate size will be five miles, but if the trace is wider, then it will be more efficient since the etching part becomes easier with this type of trace.
• The fabricator also needs accurately measure the trace width on the basis of maximum current. It usually takes up to traces of the size ranging from 50-200 mil, but if you want to use them for more range, then you need to be aware of the specific applications. 
• For resistors and capacitors, we recommend going for thermal reliefs and small-sized traces so that these can firmly join the PCB parts. Such a step reduces the chances of heat skin and potential damage. 
• If someone does not want to use small traces, then we have a solution for that as well. Just use more layers which will expand the area for routing. But you need to do it with care since it can make the fabrication expensive and can also disturb the signal integrity. 
• Now if you want to make fabrication affordable, you need to use small-sized traces, which will also reduce the number of layers. But the process itself becomes problematic to perform. 

Conclusion

Producing high-end and industrial-grade PCBs is not an easy task. You need to take care of highly critical details during the process. Therefore, you need a veteran CM for this purpose. We hope that now you know the importance of PCB tolerance and trace width through our discussion. It’s time for you to rock your projects! We cannot wait to hear about your PCB success stories!