IPC-6012 and IPC-A-600 Standards in PCB Design
In the process of manufacturing almost any product, various deformations appear, which is unpleasant, but, as a rule, inevitable PCB manufacturing is no exception. The problem of the appearance of deformations in printed circuit boards is not new, and many methods have already been developed to prevent or reduce such defects at different stages of the production process.
Bending and twisting may occur due to exposure to high temperatures and humidity. The appearance of such deformations can lead to rupture of conductors and significantly complicate the process of installing components mounted on the surface of a printed circuit board.
At the moment, most of the suppliers of printed circuit boards in Asia and Europe are guided by the requirements of IPC (Association Connecting Electronics Industries) standards. Therefore, in order for the board to turn out the way the designer intended it, it is necessary to take into account the requirements of two different standards. The following will describe the requirements of GOST and IPC for deformation of printed circuit boards.
Let’s Find out What the Warping and Twisting Deformations are and What the Standards Say About it.
Bend is a deformation characterized by a cylindrical or spherical curvature of the base of the printed circuit board (Fig. 1). In this case (if the product is rectangular) all four corners lie in the same plane.
Twisting is a deformation characterized by a spiral curvature of the opposite edges of the PCB base (Fig. 2), that is, it runs diagonally so that one corner of the PCB is not in the plane in which the other 3 corners lie. In fig. 2 points 1, 2 and 3 lie in the same plane.
Figure: 1. Twisting deformation
What does GOST Say About IPC-6012 and IPC-A-600?
According to GOST 23752-79, the deformation during bending and twisting of printed circuit boards with a rigid base, with the exception of the end contact area, should not exceed the values indicated in the table by 100 mm of length.
Table. GOST requirements for deformation of printed circuit boards
|PCB thickness(mm)||Deformation of the printed circuit board(mm)|
|On the basis of a paper||Based on glass fabric||On the basis of a paper||Based on glass fabric|
Note. The deformation values for PP with a thickness of 1.0 mm and less are not established.
When using a dielectric of the highest quality category based on fiberglass, the deformation should not exceed 0.4 mm.
Deformation in the area of end contacts should not be more than 0.5 mm, for MPP ?? 0.4 mm.
The deviation from the perpendicularity of the sides of a rectangular PCB should not be more than 0.2 mm per 100 mm, unless other values are indicated in the CD.
How to Determine the Amount of Deformation of according to GOST?
Deformation of IPC-6012 and IPC-A-600 is checked for compliance with the requirements of standards using a ruler, the weight of which, when applied to the tested PCB, does not change the value of its deformation.
A ruler larger than the diagonal length of the used PP is applied to the PP, which lies concave side up. Determine the place of maximum deviation of the concave surface from the ruler and measure it with an accuracy of 0.1 mm.
The distance between the points of contact of the ruler with the surface of the PCB is measured with an accuracy of 0.5 mm. The value of PP deformation per 100 mm of length ( K ) is determined by the formula:
K = (100 2 × h ) / L 2 ,
where is h maximum distance from the surface of the PP to the ruler, mm; L ?? distance between the points of support of the ruler, mm.
To measure the deformation value in the area of the end contacts, the ruler is placed above the end contacts parallel to the edge of the PCB.
It is also allowed to measure the deformation value using a calibration slot.
Checking the deviation from the perpendicularity of the sides of the rectangular PP for compliance with the requirements of the standards is carried out by comparing the PP with calibrated angles, one of which is made with the upper limit deviation from perpendicularity, the other with the bottom.
What does the IPC Say About IPC-6012 and IPC-A-600?
According to IPC-A-600G requirements for PCBs that use surface-mounted components, warping and twisting deformations of the PCB should not exceed 0.75%. For all other PCBs, warping and twisting deformations should not exceed 1.5%, regardless of the thickness of the printed circuit board.
How to Determine the Amount of IPC Strain?
In order to measure the bending strain, the board must be placed on a flat surface. You need to measure the values of length, width and diagonal (Fig. 2). We will need the length and width values to determine the bending deformation value in%, and the diagonal values to determine the value of the twisting strain in%.
Figure: 2. Dimensions of the PCB required to verify compliance with the IPC standard:L length; W width; D diagonal
The ends of the board should touch the surface on which the board rests. The measured value of the maximum deflection is indicated as R L if the deflection is in length, or R w if it is in the width.
After all the necessary measurements have been made, we calculate the bending deformation value using the formula:
B L = R L / L × 100 or B w = R w / W × 100.
For example, we have a 50x200mm rectangular PCB. The measured strain along the length ( L = 200 mm) is 1.5 mm ( R L ). Then we get:
B L = 1.5 / 200 × 100 = 0.75%.
This deformation is allowed by the IPC standard, even for PCBs with surface mount components.
Now let’s define the twist deformation. To do this, we need the previously measured diagonal length ( D , mm). We measure the maximum deviation from the plane, as shown in Fig. 3
Figure: 3. Deviation of the board angle from the plane during twisting deformation: R maximum deviation of the board angle from the plane;B, C, D board corners lying in the same plane (when measuring deformation, these corners must touch a flat surface)
The amount of twisting deformation in% is determined by the following formula:
Curl = R / (2 × ( D )) × 100.
For example, we have a rectangular PCB with a diagonal of 200 mm. The maximum deviation from the plane (measured R value ) is 3 mm.
Now let’s calculate the deformation value:
Curl = 3 / (2 × 200) × 100 = 0.75%.
This deformation is allowed by the IPC standard, even for PCBs with surface mount components.
What does This Mean?
The GOST and IPC requirements for this type of deformation are different. This must be taken into account if you plan to order printed circuit boards in factories operating in accordance with the international IPC standard.
- It should be remembered that GOST does not regulate the values of bending and twisting deformations for printed circuit boards less than 1 mm thick, but IPC does.
- The amount of bending and twisting strain is important when using surface mounted components. Too large values of such deformations will prevent the printed circuit board from assuming the flat state necessary for applying solder paste through a stencil (in a special printer) and for installing surface-mounted components (in an automatic installer). The IPC standard has different strain rate requirements for surface mount and non-surface mount boards. The GOST does not emphasize this.
On the other hand, warping and twisting strain values are very important for boards with end contacts, this is required by GOST, and the IPC defines them the same as for boards with or without surface mount.
How can You Prevent too Large Deformations of IPC-6012 and IPC-A-600 for the Finished PCB at the Design Stage?
Of course, there are a large number of ways to prevent and reduce deformations at different stages of the PCB manufacturing process. These methods and methods have long been successfully implemented and are widely used.
But it turns out that there are techniques, the use of which will allow, if not to eliminate, then at least significantly reduce the magnitude of deformations at the design stage. Let’s consider each of them sequentially.
This method involves filling the copper-free areas on the PCB with copper foil (Figure 4). If the conductive pattern is uneven, the thickness of the copper layer in the finished product will be different in different areas of the PCB, which may even make it impossible to manufacture this PCB.
Irregularity in the pattern of copper conductors leads to deformation of printed circuit boards (bending and twisting). The pattern of the inner layers must also be uniform in order to reduce the risk of deformation. A correct and balanced printed pattern aligns the surface of the PCB (Figure 5).
Figure: 4. Printed circuit board without copper balance
Figure: 5. PCB with copper balance
If the supply of printed circuit boards is planned in panels with technological fields, then it is necessary to add copper to the fields of the PCB ?? for balance to prevent the occurrence of bending and twisting deformation (fig. 6).
Figure: 6. An example of filling with copper technological fields of a printed circuit board
Filling free areas with copper can be different in shape, it can be squares, rectangles, circles and even just a polygon filled with copper completely or covered with it in the form of a grid (Fig. 7).
Figure: 7. Filling empty spaces with copper foil in the form of a flooded landfill,It is not difficult to redesign PCBs during development.
Figure: 8. Filling empty spaces with copper foil in the form of a grid
If you are designing a board in such a CAD system, then the easiest way is to use a polygon fill (you can do either a solid fill or a mesh fill) ?? it is a standard feature of all CAD PCB design systems.
Filling process fields is easier to accomplish during the pre-production stage when the board is being animated. In fig. 11 shows the standard options for the common CAM system for filling technological fields. There are many options: filling with a solid polygon, mesh filling, filling using circles or squares, the size and frequency of which is set by the technologist when preparing the project for production.
Figure: 9. Interface of the CAM-system for selecting the filling parameters
A board with a good balance of copper across the entire surface (Figure 10) significantly reduces the amount of strain.
Figure: 10. Example of a finished panel with a good copper balance
For PCBs with a finish thickness of 0.8 mm or less, it is best to use immersion coatings (such as ENIG coatings, Electroless Nickel / Immersion Gold? Immersion gold over nickel or IS, Immersion Silver? Immersion silver, etc.). ). The use of the popular “standard” hot tinning (HAL or HASL ?? Hot Air (Solder) Leveling) increases the strain value. This is due to the high temperature of the hot tin plating process, which can reach 270 ° C for lead-free HASL.
Symmetrical Structure for MPP
Try to use a symmetrical structure for multilayer PCBs. Using an asymmetrical structure leads to unacceptably large bending of the board.
In fig. 13a, we see an absolutely symmetric structure: prepreg 2116 is the center, with respect to it, identical, symmetrically located foil dielectrics, prepregs and electrolytic copper foil of the outer layers are used. It is safe to say that the amount of bending and twisting of PP with such a structure will be within the standards.
Figure: 11. Layer structure of a multilayer printed circuit board: a) symmetrical, b) asymmetric
In fig. 11 shows an asymmetric structure: the center is the same prepreg 2116, but dielectrics of different thicknesses are located relative to it (FR-4 with a thickness of 0.2 mm and 0.1 mm, respectively). The thickness of the foil relative to the center of the board is also different: 105 and 35 microns. Therefore, it is very likely that the deformation of the finished board will go beyond the tolerance.
The appearance of IPC-6012 and IPC-A-600 deformations on printed circuit boards is always unpleasant and sometimes gives a lot of difficulties. But if you think about the finished board at the design stage, then many problems can be avoided. Using fairly simple techniques, you can significantly improve the quality of the finished product.
It is also always necessary to remember where (in which country) and in which production an order for the manufacture of a printed circuit board will be placed, and take into account the standard against which the finished product will be evaluated, whether it will meet your expectations.
The best way can be considered a close cooperation between the designer of the board and the technologist of the plant where the board will be produced.
Indeed, in this case, even before starting the layout and routing of the board, you can find out all the necessary technological restrictions and put on the board the value of the gaps / widths of the conductors, the layer-by-layer structure, make the copper balance, determine the most optimal finish coating, etc.
Of course, all the recommendations given in the article are unambiguous and in any case, it is sometimes impossible to implement in practice for any board. For example, it may be impossible to balance copper for microwave boards.
In specific projects, it is sometimes difficult to make the board structure symmetrical. You should always proceed from the principle “of two evils choose the lesser.” But if it is possible to use the described techniques on the board, why not use them and improve the quality of the finished product without any additional costs?
IPC-A-600H Standard & Training
The first two articles in this series focused on the design of printed circuit boards ( PCBs ) using the IPC-2220 series of standards and the IPC-7351B standard, the selection of PCB base materials using the IPC-4101C standard, and the IPC-series of standards for evaluating PCB parameters and characteristics. 6010, helping to establish the general requirements and responsibilities of suppliers and consumers of printed circuit boards.
In the third article, we will look at some of the defects that can form on printed circuit boards if the supplier does not have the procedures and manufacturing capabilities to control incoming design data, fabricate the PCB and perform the necessary tests to ensure the quality of the supplied printed circuit boards. and requirements for them in accordance with the IPC-A-600H standard
The Printed Circuit Board is the Most Important Element of an Electronic Product
The IPC Association was founded by 6 PCB suppliers in 1957 in Chicago, and the main prerequisite for this was the need to develop standards to improve the quality and reliability of PCBs . Today, PCBs are not a piece of plastic with multiple copper conductors. They are often very complex products that determine whether a device will fail immediately, last for a while, or last for many years under specified operating conditions.
If the PCB supplier does not validate the incoming Gerber data, does not apply the specified base materials, does not have procedures for mechanical, chemical, optical and electrical testing,.
Throughout the entire production cycle, the multilayer board is heated several times. One of the weakest points of the PCB design is the connection of vias with the inner layers.
In fig. 5, a metallization crack can be seen at the edge of the metallized hole.
Figure: 12. Crack in hole metallization
The spread in the CTE (coefficient of thermal expansion) values largely depends on the base material of the PCB (IPC-4101C standard). If the board is subjected to multiple temperature cycles and the base material has a large CTE, a crack occurs in the hole metallization (Figure 12),
Figure: 13. Crack of metallization at the edge of a metallized hole
An electrical test prior to topcoating can identify this defect as a rupture. In this example, the topcoat was completed before the electrical test, the board passed it successfully and was shipped as good quality.
As the use of matrix-pinned and die-scale components (BGAs and CSPs) expands with increasingly smaller pin pitches, solder mask alignment becomes a challenge (Figure 6). In the example above, the solder mask is close to covering a portion of the BGA pad, which can lead to BGA soldering problems due to a loose stencil and “scooping out” of the solder paste .
Acceptance Criteria for PCBs according to IPC-A-600H-2010
This IPC standard describes the preferred, acceptable and unacceptable phenomena that can be seen on the surface or inside a printed circuit board. Examples of such phenomena are shown in Fig. 1-5. The standard provides a visual interpretation of the minimum requirements set out in various PCB standards such as the IPC-6010 series and the J-STD-003B standard.
The purpose of the illustrative illustrations in the standard is to provide an illustration for specific criteria related to the requirements of the current IPC standards. To be able to use this standard and the information it contains, the printed circuit board must meet the design requirements of the applicable IPC-2220 series standard and the PCB parameter requirements of the applicable IPC-6010  series standard. If the circuit board does not meet these or equivalent requirements,
Examples that represent only a small part of the content of the IPC-A-600H standard:
- Characteristics determined by visual inspection and inspection of the internal structure.
- Base material and condition below its surface.
- Solder coating and fused tin-lead alloy.
- Plated through holes. General information. Holes obtained by drilling and punching.
- Solder mask.
- Tests for the level of purity.
What is Acceptable and What is Unacceptable?
Most of the drawings and photographs included in the IPC-A-600H standard reflect three levels of quality for each defined characteristic, namely, desired state, acceptable state, and invalid state. The text accompanying each level establishes an “acceptance criterion” for each product class. Please note that the choice of IPC class, 1st, 2nd or 3rd, can be made through discussions between customer and supplier.
In fig. 7 shows how important the location of the drilled hole is and what is considered acceptable for the various IPC grades. The conclusion drawn from Fig. 1 and 2, is that these CAD systems must be prepared so that the PCB manufacturer can meet the IPC requirements.
Desired state – classes 1, 2, 3:
Holes are in the center of the pads.
Acceptable – class 3:
- The holes are not centered on the pads, but the girdle is 0.050 mm (0.0020 inches) or more.
- The minimum shoulder on the outer layer can be reduced by 20% of the minimum allowable shoulder in the measurement area due to defects such as pits, dents, scratches, pinholes or bevels.
Location of the drilled hole and what is considered acceptable for the various IPC grades.
IPC Training & Certification IPC-A-600H
If your business is about quality PCB manufacturing, you know that printed circuit boards affect almost all electronics in the world. For many years, IPC-A-600 Acceptance Criteria for Printed Circuit Boards and IPC-6012 Assessment and Performance of Rigid Printed Circuit Boards have set the standard for quality and reliability in printed circuit boards.
The IPC-A-600 training and certification program helps individuals from all segments of the electronics switching industry to better understand PCB quality issues, significantly enhances the understanding between PCB manufacturers, their suppliers and customers, and provides industry professionals with a valuable certificate and recognition companies.
|Acceptable – Class 1: The crack is only permissible on one side of the foil and does not extend through the entire thickness of the foil.||Unacceptable – Grades 1, 2, 3: The defect does not meet the above criteria or is outside the acceptable range.|
|A crack in the foil under certain conditions can be tolerated for class 1, but not for classes 2 and 3||Figure: 14. According to IPC-A-600H, a crack in the metallization of the wall is not allowed for all classes|
|Unacceptable – Grades 1, 2, 3: The defect does not meet the above criteria or is outside the acceptable range.||Desired state – classes 1, 2, 3: the solder mask is located concentrically around the copper pad with a gap.|
|Figure: 15. This type of defect is unacceptable for all classes||Figure: 16. Compare with fig. 6: the difference is obvious|
Who Needs IPC-A-600H Training?
Manufacturers of Printed Circuit Boards
Knowledge of the acceptance criteria is essential to understanding the causes of unacceptable conditions arising from the manufacturing process. The IPC-A-600 training and certification program reveals an important relationship between the IPC-A-600 and IPC-6012 standards.
This program indicates to PCB consumers that the company is serious about continuous product improvement. Until recently, there was no such widely recognized and highly technical training for everyone involved in PCB manufacturing .
Electronics Assembler Companies
Nobody wants to install a lot of expensive components on a defective board. IPC-A-600 training and certification provides electronics assemblers with information on how to best organize incoming inspection.
Knowing the valid states means that boards will not be rejected unnecessarily. Knowledge of invalid conditions prevents the assembler from mounting expensive components on defective boards. Certified IPC trainers working in the electronics assembly area can provide more productive relationships with PCB suppliers.
OEM Companies and Suppliers of Materials and Equipment
Anyone involved in the supply chain or PCB specification development needs an understanding of the criteria of the IPC-A-600 and IPC-6012 standards. OEMs, like assembly companies, do incoming inspections and invest a lot of money in PCBs.
Designers can familiarize themselves with the basic requirements for the quality of boards for products of all classes. Equipment and material suppliers will work with OEMs to improve their ability to recognize invalid conditions.
What are the Benefits of the IPC-6012 and IPC-A-600standard, as well as Training and Certification?
Those interested in quality assurance throughout the company receive an industry-designed, industry-accepted and IPC-implemented program to support their commitment to continually improving performance and product quality. The visibility of the IPC assures consumers that your company is serious when it applies and undergoes IPC-A-600H training.