Book Link is Here..
This is an old book but still useful and good techniques to reduce noise in electronic systems.
This is one of the best guidelines I have come across.
Friday 2 August 2019
Reference Book and PCB Design Guidelines
Book Link is Here..
This is an old book but still useful and good techniques to reduce noise in electronic systems.
Thursday 30 May 2019
Clearance Holes for Metric Fasteners
When we do PCB board design, it is good to know how much clearance we need for screw holes. General Screw size and clearances for holes can be seen in the table below.
PCB Design : Via Current Carrying Capacity
Maximum via current carrying capacity can be calculated using Saturn PCB Design Toolkit
Commonly used via size and current carrying capacity are as below.
Friday 3 May 2019
Wednesday 9 January 2019
DepanelingTab Routing
Board assemblies can be de-tabbed using perforated breakaway tabs, v-grooves break away tabs, or hand-cutting with a de-tabbing tool. For Tab and V-Score (i.e. PCB's that must be sheared along an edge):
1. Traces and vias should be a minimum of 0.050"(1.27 mm) away from routed/scored edge.
2. Components should be a minimum of 0.100"(2.54 mm) away from routed/scored edge.
These rules are to help prevent components or board damage during the depaneling process and prevent flooding during the wave soldering process.
For 0.062" (1.6 mm thickness) Printed Circuit Boards:
1. Perforation holes should be typically spaced at 1 mm intervals.
2. Tab routed with 1 mm radius.
3. Routed slot should be 2 mm minimum, for single image panels. Use 3 mm routed slots when two or more boards are in a panel. This allows for more accurate edge dimensions.
4. 75 mm typical distance between tabs, not to exceed 100 mm.
5. Place tabs approximately 25 mm from corners to reduce sagging during reflow or wave soldering.
6. Desirable to have at least one tab per side.
7. Slight inset of perforation is preferred; it provides an edge which requires little or no additional labor to clean up.
NOTE: Two parallel edges are required for a PCB to be processed in the SMT line. This is to prevent skewing through the conveyor system. All odd shaped PCB's MUST have edge rails incorporated to meet this requirement. Custom reflow fixtures will be made if this requirement is not met.
1. Traces and vias should be a minimum of 0.050"(1.27 mm) away from routed/scored edge.
2. Components should be a minimum of 0.100"(2.54 mm) away from routed/scored edge.
These rules are to help prevent components or board damage during the depaneling process and prevent flooding during the wave soldering process.
For 0.062" (1.6 mm thickness) Printed Circuit Boards:
1. Perforation holes should be typically spaced at 1 mm intervals.
2. Tab routed with 1 mm radius.
3. Routed slot should be 2 mm minimum, for single image panels. Use 3 mm routed slots when two or more boards are in a panel. This allows for more accurate edge dimensions.
4. 75 mm typical distance between tabs, not to exceed 100 mm.
5. Place tabs approximately 25 mm from corners to reduce sagging during reflow or wave soldering.
6. Desirable to have at least one tab per side.
7. Slight inset of perforation is preferred; it provides an edge which requires little or no additional labor to clean up.
NOTE: Two parallel edges are required for a PCB to be processed in the SMT line. This is to prevent skewing through the conveyor system. All odd shaped PCB's MUST have edge rails incorporated to meet this requirement. Custom reflow fixtures will be made if this requirement is not met.
Tuesday 8 January 2019
SMD and NSMD Pad Configurations
Two types of PCB solder mask openings commonly used for surface mount leadless style packages are:
1. Non Solder Masked Defined (NSMD)
2. Solder Masked Defined (SMD)
As their titles describe, the NSMD contact pads have the solder mask pulled away from the solderable metallization, while the SMD pads have the solder mask over the edge of the metallization, as shown above. With the SMD Pads, the solder mask restricts the flow of solder paste on the top of the metallization which prevents the solder from flowing along the side of the metal pad. This is different from the NSMD configuration where the solder will flow around both the top and the sides of the metallization.
Typically, the NSMD pads are preferred over the SMD configuration since defining the location and size of the copper pad is easier to control than the solder mask. This is based on the fact that the copper etching process is capable of a tighter tolerance than the solder masking process. This also allows for visual inspection of solder fillet.
In addition, the SMD pads will inherently create a stress concentration point where the solder wets to the pad on top of the lead. This stress concentration point is reduced when the solder is allowed to flow down the sides of the leads in the NSMD configuration.
1. Non Solder Masked Defined (NSMD)
2. Solder Masked Defined (SMD)
Typically, the NSMD pads are preferred over the SMD configuration since defining the location and size of the copper pad is easier to control than the solder mask. This is based on the fact that the copper etching process is capable of a tighter tolerance than the solder masking process. This also allows for visual inspection of solder fillet.
In addition, the SMD pads will inherently create a stress concentration point where the solder wets to the pad on top of the lead. This stress concentration point is reduced when the solder is allowed to flow down the sides of the leads in the NSMD configuration.
Cool Electronic Circuit Simulator
This online circuit simulator is easy to use and useful for simple circuit simulations.
Altium Designer : Defining Solder Mask Expansion/ Relief
Altium default value is 4 mil and solder mask expansion can be defined according to PCB manufacturer capability.
Design for manufacturing or DFM
Design for Manufacturability rules and guidelines are a collection of PCB design best practices to help our design be as easily manufacturable as possible. The easier it is to manufacture a PCB, the more likely it will be to reduce both manufacturing errors and costs. DFM rules have been developed by PCB manufacturing experts and they will vary depending on the design technology of the board, and the capabilities of the manufacturer.
It is highly recommended to check with PCB manufacturer for their precision and limit on the width of solder mask Dam.Solder mask dam between surface mount pads will prevent solder bridging during assembly. Below is one of the PCB suppliers' capability.
In summary, solder mask dam width depends on the copper thickness and solder mask colour. Generally, 3 mil of solder mask dam can be achieved using 1oz of copper but that will be 6 mil for 2 oz of copper.Similarly, minimum solder mask dam for Green solder mask is 3 mil and others will be 5 mil.
In order to get solder mask dam between pads (if individual relief is required) spacing between copper should be 8 mil or more. Otherwise, finish PCB will get block relief without solder mask dam.
PCB under microscope with and without solder mask dam can be seen in the photo below.
It is highly recommended to check with PCB manufacturer for their precision and limit on the width of solder mask Dam.Solder mask dam between surface mount pads will prevent solder bridging during assembly. Below is one of the PCB suppliers' capability.
In order to get solder mask dam between pads (if individual relief is required) spacing between copper should be 8 mil or more. Otherwise, finish PCB will get block relief without solder mask dam.
PCB under microscope with and without solder mask dam can be seen in the photo below.
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