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By Mer-Mar Electronics | Date posted: | Last updated: August 18, 2022
PCB manufacturing tolerances

It is imperative that when you offer the documentation for PCB manufacturing, all the requisite details are provided. Very often there are missing details that, if provided, can go a long way in quoting the right cost as well as manufacturing PCBs that match up to your bespoke requirements. Robust data needs to include tolerances as they will ensure there are no defaults in manufacturing as well as no production delays. Let us look at these tolerances in some detail:

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When it comes to components, tolerance refers to the acceptable variant to be able to ensure proper functioning. Tolerance in this case also refers to the difference in between the lower & upper dimensions of the component parameters.

The overall functionality of the PCB is dependent on how the components perform with each other and therefore it is important to know the limit of each component. Component tolerance modeling is thus a crucial step that ensures reliability testing of the board to determine if the board components succeed in performing as a unit. In fact component tolerance modeling allows the quantification of how individual components relate to the output. The more accurate the tolerance, the more reliable the final product will be. Component tolerance modeling, therefore is an important function of the design as well as the manufacturing process.

What is important to remember is also that since each component brings its own component limit, what needs to be considered is the tolerance stack-up or what is the additive effect of various component tolerances. The tolerance stack-up estimates the effects of the accrued variations & is defined on an engineering design.

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When it comes to PCB laminate materials, it is important to provide specific Tg ratings. Additionally providing a stack-up with specific dielectrics is important. What you also need to provide so that the right material can be selected is the overall printed circuit board thickness. What is needed here is a certain material tolerance since it will be impossible to meet the exact details. If your requirement is for a tolerance less than 10 percent, you might need a change in the core as well as a tighter process control. In turn this will lead to added costs. Materials & cores therefore need to be correctly chosen at the prototype stage as if this is done at the production stage, it can prove to be far more costly.

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What is also needed when creating a fabrication document is the need to look at PCB manufacturing tolerances to avoid PCB fabrication errors.

For example, plated and non-plated holes need to come with different tolerances as drills cater to specific sizes with strict tolerance. It is important to remember that there are many factors that affect the size of the hole. Some of these include:

  • Plating baths
  • Time in & out of the tanks
  • Additional plating
  • Etching
  • Finished Plating

The need for tolerances is therefore a given. However it is important to remember that not all drills are exact, so some amount of tolerance is required. Where tighter tolerances are required, it is imperative that they should be noted clearly.

In fact, larger holes, plated or non-plated above the size of 0.200”, will require a tolerance of +\-0.005”.

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When it comes to routing, tolerances are required right from slotting tools to routing cutoffs. Typically, a tolerance of +\-0.005” is the default standard on the size or cut.

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Following is the analysis of outer layer (width annular ring, min annular ring, NP to copper, KO to copper, etc.):

Outer copper thickness 1OZ 2OZ 3OZ 4OZ
Compensation value 0.01mm 0.02mm 0.03mm 0.04mm
Normal trace/spacing 0.12MM 0.15MM 0.2MM 0.25MM
Normal Width between pads 0.12MM 0.15MM 0.2MM 0.25MM
Normal Width between pad and trace 0.12MM 0.15MM 0.2MM 0.25MM

Normal Width between pad or tarce and copper area

0.2MM 0.2MM 0.2MM 0.2MM
Normal VIA pad single side width 0.15mm 0.16mm 0.17mm 0.18mm
Normal PTH pad single side width 0.2mm 0.21mm 0.22mm 0.23mm
Normal Width between NP   holes and copper 0.2mm 0.2mm 0.2mm 0.2mm

Normal Width between profile and copper

0.3mm 0.3mm 0.3mm 0.3mm
Normal width between via and copper 0.2mm 0.2mm 0.2mm 0.2mm
Max trace/spacing 0.1MM 0.13MM 0.18MM 0.23MM
Max width between pads 0.1MM 0.13MM 0.18MM 0.23MM
Max width between pad and trace 0.1MM 0.13MM 0.18MM 0.23MM
Max width between pad or trace and copper area 0.18MM 0.18MM 0.18MM 0.18MM
Min width between NP holes and copper 0.15mm 0.15mm 0.15mm 0.15mm
Min Width between profile and copper 0.25mm 0.25mm 0.25mm 0.25mm
Min width between V-Cutline and copper 0.35mm 0.35mm 0.35mm 0.35mm
Min width between via and copper 0.18mm 0.18mm 0.18mm 0.18mm

To sum up

Tolerance modeling is a wonderful way to achieve a balance between performance & cost as otherwise the less the tolerance, the more the cost of production. Tolerance modeling therefore is the key aspect that reduces manufacturing cost while ensuring that the quality is maintained.

Of course, in case you do not specify the details in the manufacturing document, the contract manufacturer will refer to the IPC standards & performance specifications as a guide. However detailed information on aspects such as surface finish copper weights, material, hole sizes and more can go a long way in ensuring that the final product matches your bespoke needs.

One of the top PCB manufacturing firms, Mer-Mar Electronics offers complete packages for PCB assembly. Customers appreciate our reliable quality and quick turnaround, seeing us as a one-stop shop for all their PCB manufacturing needs.

Please do not hesitate to contact our team if you have any questions about our PCB assembly and PCB manufacturing service, or if you require immediate assistance. Send us an email at sales@mermarinc.com or give us a call at (760) 244-6149 with any questions you may have.

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By Mer-Mar Electronics | Date posted: | Last updated: June 25, 2022
Flexible Multilayer PCB

Flexibility is the cornerstone of great design and that is something that is made possible by flexible multilayer PCB.

A flexible printed circuit is a circuit board with a flexible construction. It is also known as a flex circuit. It is used in small electronics. A flex circuit largely consists of two or more copper conductive layers with an insulation material between its layers. There is also an application of coverlay in the flexible areas that can protect the external circuitry of a flexible PCB.

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Flex and rigid-flex circuits are available in a wide range of configurations and can be found in different applications. These include:

  • Single-layer flex printed circuits – Such circuits adhere to IPC 6013, Type 1 standards & have a single copper conductive layer between two insulating layers. These work well in bend-to-fit applications.

  • Double-sided flex printed circuit – Adhering to IPC 6013, Type 2 standards, these consist of two copper conductive layers with insulating polyimides. Plated through-holes ensure circuit connectivity between the layers. Such circuits work well for dynamic flex as well as bend-to-fit applications.

  • Multilayer flex printed circuit – Adhering to IPC 6013- Type 3 standards, they have three or more conductive layers with insulating layers in between. They also make use of plated through-holes for ensuring connectivity between layers. They also use high-speed controlled impedance and work well for bend-to-fit applications.

  • Rigid-flex printed circuit – They adhere to IPC 6013-Type 4 standards. These have two or more copper conductive layers with insulation in between. They also have plated through-holes that cut through the rigid as well as flexible layers. In addition, there is an application of coverlay on the flex layers.

Of these, let us look at multilayer flex circuit boards in greater detail:

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One can look at multilayer circuits as a combination of several single layer or double layer circuits. Multilayer circuits can in turn come with:

  • Continuous lamination
  • Without continuous lamination

The choice of the above depends upon whether you are looking at maximum flexibility in your multilayer PCB designs. For designs that need total flexibility, it is an easy decision that continuous lamination is not suitable. Multilayer flex circuits work particularly well in the following scenarios:

  • Specified impedance requirements
  • When you need to eliminate crosstalk
  • Where there is extreme component density, and more.

In fact, if one were to look at the benefits of multilayer flex printed circuits, these would include:

  • High circuit density
  • No need for mechanical connectors
  • Flexibility in design
  • Reduction in weight as also size
  • Ability to function in high operating temperature range
  • Reduction in wiring mistakes
  • Improved signal quality
  • Improved impedance control

In addition, with multilayer flex PCBs you also tend to benefit from:

  • Reduction in assembly errors. This is because they do not use hand-built wire harnesses and make use of automation in production.
  • Reduction in assembly time. Because the multilayer PCB assembly doesn’t require too much manual labor, both the assembly time & the cost are kept under check.
  • High applicability. Flexible circuits also offer a lot of design freedom and therefore lend themselves to many applications. They also offer flexibility during installation without losing functionality. Importantly, they lend themselves to high-density component placement which is a great plus in today’s times of miniaturization.
  • Improved airflow. With their designs offering improved airflow, increased product lifecycle is a given. Their compact design also lends itself to better dissipation of heat.
  • Increased reliability. With fewer interconnections what flexible multilayer printed circuit boards also offer is increased reliability. That they are durable and can withstand elevated temperature conditions is an added advantage.

Because of all these factors & particularly the fact that they lend themselves to small size applications, multilayer flex circuits are so much in vogue. That they can withstand harsh environmental conditions is another advantage as that means that they can be deployed in tough environmental conditions.

It is however important to select the right contract PCB manufacturer that has the requisite experience & expertise with multilayered boards. They are equipped with robust PCB design software as well as industry best practices that ensure you do not have to deal with costly errors later that can lead to product recall and even cost the company’s reputation. If you are dealing with mission-critical operations, the use of multilayer flex circuits particularly cannot be overestimated.

Mer-Mar Electronics is an ISO 9001:2015 certified company and ITAR (International Traffic in Arms Regulations) compliant manufacturer that delivers multilayer PCB fabrication services with specialized support, reliable testing, and multi-functional features. In case you have any questions or require more information about PCB assembly and fabrication services, get in touch with us via sales@mermarinc.com or call us on (760) 244-6149.

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By Mer-Mar Electronics | Date posted: | Last updated: June 20, 2022
Printed Circuit Board Material

Effective material management is imperative in all aspects of our lives. However, for PCBs, especially those which work in high-frequency applications, the choice of the right material is beyond crucial. The performance of the board is often seen as a function of component placement and trace routing. However, it is the circuit board material that offers a strong foundation.

Let us look at some of the benefits that high-speed board materials offer:

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The major benefits of high-speed board material include:

  • Impedance Control – High-speed board material has a dielectric constant of +/- 2% or better. For circuits that require controlled impedance routing this is extremely important.
  • Signal Performance – A lower dissipation factor that helps to reduce signal loss is extremely important especially as the frequency of transmission line increases.
  • Dimensional Stability – In a high-frequency design it is imperative that tight physical tolerances be maintained. Laminate materials that offer mechanical stability are therefore key.
  • Moisture absorption – A small amount of moisture can also come in the way & impact electrical performance.
  • Thermal Management- For boards that have to be used in harsh environments, materials with excellent thermal properties need to be chosen.

The above are the exact reasons why FR-4 has a number of operating limitations that affects its efficacy. Some of these include:

  • FR4 is rated at a dielectric constant of ± 10% or more, that does not give it the tolerance that is required for high-frequency designs.
  • It has a high dissipation rate when it comes to signal loss.
  • Its moisture absorption rating is nearly 50%, that can affect electrical performance of the board.
  • It also has limitations in terms of thermal management & therefore is not suitable for high-temperature operating conditions.

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The demand for high-frequency PCB manufacturing is on the rise in several sectors including but not limited to:

  • Automotive radar systems
  • Satellite antennas
  • Cellular telecommunication systems
  • Broadcast satellites
  • RFID tags
  • Missile Guidance systems, and more.

For these and many other sectors, there are a number of circuit board materials that work particularly well. Some of these include:

  • Epoxy resins – This category, of course, includes FR4 which suffers from some weaknesses when it comes to higher frequencies.
  • Enhanced epoxy – These materials tend to improve the performance as opposed to standard FR 4 & related material.
  • Polyimide – Such material can withstand harsh conditions with their excellent thermal & mechanical properties. Additionally, they are chemical as well as moisture resistant.
  • PTFE (Polytetrafluoroethylene) – Also referred to as Teflon, such materials offer high impedance control as well as signal performance making them highly suitable particularly for wireless communication systems.
  • Thermoset hydrocarbon laminates – These are particularly known for their mechanical stability although at higher frequencies they may show dielectric loss.

There are a wide variety of materials available for high frequency applications. Some of the aspects to be mindful of, however, include:

  • Such material comes at a higher cost. You therefore need to look at a cost-performance trade-off in making your choice.
  • Sometimes you will need to evaluate exactly how much performance improvement your circuit needs. After a close evaluation, you may at times want to settle for FR-4 or one of its enhanced versions.
  • Many of them require non-standard fabrication processes adding to fabrication & assembly cost.
  • They may require changes in solder types as well as cleaning processes that impact both manufacturability & price.

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Given the criticality of the operation & the many factors to be considered in choosing the right material, the one thing that is non-negotiable is to choose an experienced electronic contract manufacturing partner who can guide you through the choice of material. The contract manufacturer will be able to undertake the right cost-benefit evaluation to choose a material that meets your criteria without escalating the cost to unacceptable levels. Additionally the contract manufacturer can also help you with the right board layer stack up strategy. You can also use some sophisticated design tools that are meant for high frequency designs.

Our experienced PCB material management team and advanced material management system can efficiently manage your projects and requirements. We have the resources available to locate parts and materials you need to eliminate the delay and reach quickly to the result. In case you have any questions or require more information about PCB Manufacturing, contact us via sales@mermarinc.com or call us on (760) 244-6149.

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By Mer-Mar Electronics | Date posted: | Last updated: June 15, 2022
Copper Thieving in PCB

Copper thieving in PCB refers to adding non-conductive patterns of copper to the printed circuit board. This is done to even out the electrical current used for plating the board. In the absence of this, there can be areas of the board that are isolated and where current can become more concentrated. This results in the often seen “mushroom” profile caused on account of under-etching. In turn, in can impact both the electrical performance of the trace as well as its structural strength.

To avert these issues, adding copper thieving in the areas of the circuit board where the metal is sparse is effective. It ensures that the same amount of copper is distributed throughout the board so that the plating current is applied equally and the traces will all etch the same amount.

Thieving is seen by way of an array of dots or diamonds added to what would have otherwise been an open area on the board. It is important to remember that if there are any areas on which you specifically do not want any thieving to be added, the same needs to be mentioned on the fabrication drawings. Typically thieving is avoided in the following areas:

  • Where it interferes with the controlled impedance elements on the board.
  • Where you require a smooth area to pace a label.
  • In case it violates creepage or clearance rules.

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The big advantage of copper thieving is that it makes the copper distribution uniform which helps make etching & plating seamless and ensure that different copper densities do not plate and etch at different rates. In the absence of copper thieving copper features such as traces, pads, plated vias and more that are in a more sparsely populated area tend to over plate as opposed to those in more densely packed areas.

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Thieving evens out the thickness of the finished board. If a design involves most of the copper layers being stacked on one side, there could be a noticeable change in thickness on one side as opposed to the other. Copper Thieving tends to bring about consistency in thickness in finished boards.

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With uneven copper distribution, a big disadvantage is PCB warping and twisting. This is seen more so during high PCB assembly or when copper begins to heat and expand. Copper thieving goes a long way in minimizing warpage.

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Thieving is also an important way to control the dielectric thickness between copper layers. During the lamination cycle the layers are stacked together using pre-preg. Once it is heated the pre-preg liquefies and fills the gaps between the copper features. By doing this, it ensures no air is trapped inside the board. With uneven copper distribution, you will often be left with inconsistent dielectric thickness.

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While the advantages of Copper Thieving are many, it is important to keep in mind the fact that if there are traces on the layers just below where thieving has been added, it can impact the impedance of these traces. It is imperative therefore to add a note to your fabrication drawing to state that thieving should not be done in these areas.

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Thieving is an effective method to ensure that there is uniform plating of copper. To ensure this the plating current needs to be uniformly distributed over the PCB outer layer surfaces. It is imperative that you work closely with your PCB Contract manufacturer so that the copper thieving works for both plating and signal performance needs of the board. An experienced contract manufacturer will understand these requirements and can advise you on the creation of the thieving patterns. It is critical that any metal changes to the board are undertaken by the design engineers, who can look at the issue holistically, and can take all of the potential effects into account. It is important to remember that there is a lot to consider when adding copper thieving to a printed circuit board hence the experience and access to best practices of the contract manufacturer are priceless.

Mer-Mar Electronics is one of the leading PCB design and manufacturing companies, providing all in one PCB assembly and PCB fabrication solutions. Our consistent quality and quick turnaround endear itself to our customers, who look on us as a one-stop-shop for all their PCB manufacturing requirements. In case if you have any questions or require more information about our services, contact us via sales@mermarinc.com or call us on (760) 244-6149.

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