The PCB assembly and design standards are not just there to help in constraining your productivity. Rather, they help in creating uniform expectations of the performance and designs of products across many industries. Furthermore, with standardization there are tools to ensure compliance. These include calculators for some design aspects, as well as processes for inspection and auditing and more.
For high voltage design of printed circuit boards, the significant generic standard for the PCB design is the IPC-2221. Also, the majority of the main design aspects are usually summarized in the IPC-2221 design standard. Note that some are just simple mathematical formulas. In addition, for the high voltage printed circuit boards (PCBs), the IPC-2221 calculator will aid you to determine the right spacing requirements between your PCB’s conductive elements quickly.
This ensures that the high-voltage board you manufacture remains safe at that operating voltage. Anytime the design software adds any of these specifications as the design rules, then you can stay productive. This also helps in preventing any mistakes with the layout while building your board.
In addition, the IPC-2221 is a known as the generic standard for majority of circuit board designs. Also, it helps in laying down all the requirements for the PCB design. These include the different component mounting forms and interconnection structures. Therefore, the IPC-2221 forms the basis via which the design recommendations and principles for boards become established. Now, let’s consider what the IPC-2221 standard is all about, as well as whatever design requirement that it imposes. However, before that, we will be considering what IPC standards are in general.
What are the IPC Standards?
The establishment of the IPC standards is mainly to serve the electronic manufacturing industry. Furthermore, a trade association called IPC usually issues it. During the establishment of the IPC, it mainly stood as an institute for the printed circuits. However, it was transformed into an institute that helps in the packaging and interconnection of electronic circuits.
In addition, the IPC standards lay a foundation. This is for the assembly, design, interconnection, packaging, inspection specifications, performance, and material for our electronic industry. Also, these standards are usually followed globally. Now let’s know what the IPC-2221 standard is.
What is the IPC-2221 Standard?
The IPC-2221 standard is an industry standard that is generally accepted. This helps in offering a definition to different aspects of PCB design. Examples here include the design requirements on different materials (which include plating and substrates), thermal reliefs, thermal management, testability, and annular rings.
Furthermore, some design guidelines are usually superseded by some design standards that are more specific. For instance, the IPC-6018 and IPC-6012 offers design specifications on the high-frequency PCBs and rigid PCBs respectively. Also, these added standards ought to be very consistent with IPC-2221 standards for the generic PCBs. Moreover, the IPC-2221 standard isn’t the standard used in the assessing of manufacturing defects and yield or product reliability. Also, for the rigid boards, either the IPC-A-600 or IPC-6012 will be used in qualifying the fabricated rigid PCBs.
There are some specific standards for each board type. Take for instance, in order to design the rigid PCBs, the standards included in the IPC-2221 must be referred to, as well as those outlined in the IPC-2222.
So also, this also applies to the flex, HDI (high-density interconnect) and multichip module. This is why it is very necessary that all the IPC-2221 generic standards is used in line with the standards’ detailed requirements, which are specific to a specific circuit board type.
PCB designers have to focus primarily on the balancing of the necessary thermal, mechanical, electrical performances. Furthermore, you must monitor the cost, manufacturing difficulties, as well as the reliability of the board. This is what the IPC-2221 does; it helps in focusing on all the aspects.
In addition, the IPC-2221 standard helps in covering different topics in relation to board design. For the article, we will be focusing on some important ones like insulation requirements, high-voltage design, creepage, and clearance requirements.
What is IPC-2221B in High-Voltage Design?
Usually, the IPC-2221B has the necessary design requirements for designing the high voltage PCB. One of such is the conductor clearances. The intention of this is to address two main points:
- Possibility of dielectric or corona breakdown at a high-electric field strength
- potential for the anodic filamentation, which can at times be referred to as dendritic growth
Now, the initial point is the most important. This is because you can prevent or suppress it with the right material selection, spacing, insulation, as well as general cleanliness.
The necessary spacing in preventing the effects is usually summarized as one function of that voltage present in-between the two conductors present in IPC-2221.
The values of the IPC-2221 standards list the minimum spacing of the conductor as the function of that voltage present between both conductors. Also, the specifications of the values are done with respect to the peak DC or AC voltage in-between the conductors.
Remember that the IPC-2221 specifies only the fixed minimum spacing values for the conductor for voltages of about 500 V. Immediately this voltage between both conductors surpasses 500 V, then the per-volt clearance values helps in calculating the minimum spacing of the conductor. Furthermore, each volt higher than 500 V helps in adding the necessary minimum clearance.
What is the IPC-9592B Standard on the Power Conversion Devices?
For the IPC-9592B standard, it offers the necessary requirements for the power conversion devices. In addition, the standards are consistent anytime it is graphed with the necessary conductor spacing as specified in the IPC-2221.
The spacing requirement helps in defining the minimum trace spacing as the function of the values of the peak voltage. Also, the difference here is that the standard helps in scaling the minimum spacing values of the conductor with the applied voltage less than the 500V limit.
When you search online, you will discover that some calculators are already pre-programmed with these above values. Immediately you determine these spacing values, you will be able to program them into the design rules. Due to the fact that you will have different nets all functioning at contrasting voltages, you will be able to program the values into the design rules. After this, you can set some nets nearer to themselves if the design is becoming extremely dense.
Failure in Metal Migration
Among the spacing values for the electrical conductor defined in the IPC-2221, there are some requirements that help in preventing failure in metal migration. When we talk of metal migration, it is regarded as one of the failure mechanisms for the high voltage designs having a high density for the conductors.
Furthermore, whenever the two conductors have a great and high potential, the metallic dendrites’ electrochemical growth can happen whenever the conductors contains some residues having water-soluble salts.
The metallic dendrites have the ability to short out the two points on the high density printed circuit board (PCB). Actually, this is an effect of the electric field, this describes why a minimum spacing requirement exists; increasing all the spacing present in-between the conductors for a specific potential difference aids in reducing the field in-between the conductors. This inhibits any dendrite growth.
Beyond the IPC-2221 Calculator
Please take note that the standards of IPC-2221 are voluntary. However, for the products that safety standards cover as defined in the electrical and building codes, the clearance and creepage requirements in the IEC or UL standard could be mandatory.
Take for instance, the relevant safety requirements on telecom and IT products with the battery power and AC mains could be seen in this standard – IEC 62368-1; this takes the place of the IEC 60950-1 standard). In addition, for the creepage, the specified spacing underneath the IPC-2221B is dependent on the pollution degree, working voltage of the RMS, as well as material group.
You can find the other two terms defined in the standards – UL 62368-1. Whether there is a need to adhere with the IPC, IEC, as well as other necessary safety standards, then you will be able to specify the design requirements as the design riles when using the most appropriate software for your PCB design.
In order to stop the breakdown present in-between the conductors along the layer as a result of creepage, the choice of material is as significant as the right spacing in-between the conductors. CTI (comparative tracking index) is a metric that summarizes the ability of a specific material to be able to fight against breakdown.
The CTI value of the PCB laminate material is useful in setting the creepage limits for the conductors across the substrate’s surface. Furthermore, the standard IEC-60112 helps in defining the CTI values in a case that larger substrate of CTI grade, which withstands a much higher voltage even before experiencing dielectric breakdown.
Clearance and Creepage
Right now, note that clearance and creepage goes hand in hand. Also, the determination of the spacing with respect to the clearance is a very nice place to begin. Furthermore, the building of the CAD tools as well as routing features present in the Altium Designer® is done on a rules-driven unified design engine, which automatically checks the layout while you are creating your board.
After figuring out the clearance requirements using the IPC-2221 calculator, the you will be able to program these clearances in your design rules. This ensures the safety of your board and also makes sure that is functional at a high voltage. Also, you will have access into a complete set of features. This will help you in preparing for the manufacturing as well as assembly.
What Does Clearance in Circuit Board Design Mean?
The clearance distance is that distance in-between the two nodes or conductors and measured in air. Furthermore, the IPC-2221 has to do with many clearances relating to many different aspects or sections of the printed circuit board.
What Does Creepage Mean in Printed Circuit Board (PCB)?
Clearance and creepage are the two parameters, which are linked to the distance necessary in-between the conductors present on the circuit board. Also, clearance has to do with the distance in-between two nodes or conductors present in the air. On the other hand, the creepage indicates the distance present between the nodes or conductors along an insulator’s surface.
With respect to the IPC-2221 standard, the space present in-between the conductors have to be optimized and maximized at all times to the highest extent possible. Also, you will allot the conductor spacing in a way that you create much space for the etch compensation of other features.
In addition, the etch compensation must have twice the thickness of that etched copper. Also, consider the conductor imperfections, as well as the copper wicking present in-between the adjacent plane layers and the PTH.
How Should the Thickness of the Traces Be?
In order to carry some current, the PCB trace has to possess the right thickness. Furthermore, if this is less than necessary, this trace will end up burning and the current will propagate through it. Therefore, the width and thickness will help in depending on the capacity to carry current, signal characteristics, as well as the maximum temperature that is allowable. You can determine it when you refer to the IPC-4562 and IPC-2141 also.
In addition, the traces’ thickness must change as well in line to the board’s construction requirements. If the construction of the circuit board has to do with buried or blind vias, sequential lamination, then the copper thickness present on these layers will also be dependent on the parameters.
Conclusion
Our article on IPC-2221 ends here. The IPC-2221 standard is an industry standard that is generally accepted. This helps in offering a definition to different aspects of PCB design. Furthermore, some design guidelines are usually superseded by some design standards that are more specific. Also, these added standards ought to be very consistent with IPC-2221 standards for the generic PCBs. Furthermore, for the rigid boards, either the IPC-A-600 or IPC-6012 will be used in qualifying the fabricated rigid PCBs.
