DFM Analysis

Padstack Analysis will primarily include:

 

  • Toeprint to Toeprint 

Purpose: Toeprints (pads) of different components should be kept distant from each other to prevent solder bridging during the assembly process

  • Extra Solder Mask Web 

A web is a thin line of solder mask between adjoining pads. Fine pitch components should not have a webs since they are very narrow and may break and ‘float’ on the board. These components should have ‘picture window’ solder mask which is one rectangular mask opening for each row of pads.

  • No Solder Mask Web 

Components with a large pitch can, and should, have web between their neighboring pads. This provides better isolation in case of solder smearing.

  • Special Toeprints 

Provides a means of detecting potentially problematic toeprints, such as combined THMT and SMT land patterns in one toeprint.

  • SMD Direct Connection

Provides a means of differentiating between solder which accidentally bridges between two pads during the processing of the board and an intentional trace running between two fine pitched pads.

  • Via to Via Edge 

Reports distances less than pp_v_spacing between two via pads (edge to edge).

  • Via to Toeprint 

Vias that are too close can rob heat from the toeprint during the soldering process and cause a bad solder joint.

  • Via to Other Net Toeprint 

Vias that are too close to toeprint pads can cause solder bridging.

  • Via in SMD 

Reports via holes that either touch SMD pads or are contained in pads that touch the SMD pad (either full or partial containment, or touching). SMD pads have both attributes SMD Pad and Pad Usage=toeprint. Vias assigned the attribute ICT Test Point are excluded from this category.

  • No Thieving Pad 

Wave solder processes may require an additional pad for some devices (e.g.SOIC) to collect (thieve) residual solder which remains after wave soldering is applied to the row of pads in the device.

  • Toeprint Annular Ring 

Special processes, such as Soft Beam, require unusually large annular rings around holes (about 50 mils or more)..

  • Toeprint SM Clearance 

Special processes, such as Soft Beam, require unusually large solder mask openings around holes (about 50 mils or more.

  • Gold Fingers to Capped Via 

Gold plating must be protected during soldering processes, performed with fixtures and/or masking. Capped vias may be closer than other toeprint features.

  • Gold Fingers to Uncapped Via 

Gold plating must be protected during soldering processes, performed with fixtures and/or masking. Uncapped vias must be outside the masked area.

  • Gold Fingers to Surface TP 

Gold plating must be protected during soldering processes, performed with fixtures and/or masking. Surface testpoints may be closer than other testpoint features.

  • Gold Fingers to Thru TP

Gold plating must be protected during soldering processes, performed with fixtures and/or masking. Drilled testpoints must be outside the masked area.

  • Toeprint to Plane 

Height separation between the solderpaste stencil and the toeprints of fine pitch components must be minimized to avoid excessive solder distribution.

  • Shadowing of Inline / Staggered Components 

Purpose: To detect possible solder bridging to shadowed components.

  • Shadowed THMT Toeprint

Purpose: To detect shadowing problems between components and toeprints of a THMT component located on the other side of the board with toeprints on the current side. The shadowing component could cause the solder not to be applied properly to the THMT pins.

  • Toeprint to Rout 

Toeprints should be sufficiently distant from the edge of the board to avoid solder deposit on the board edge.

  • Toeprint to Break Tab Rout 

Purpose: To identify toeprints/exposed toeprints too close to break tabs.

  • Toeprint to Conveyed Edge

Reports distances between toeprints/exposed toeprints of components and conveyed edges (edges parallel to the SMT process) in the rout layer. The test checks distances to a bounding box of the board (the smallest rectangle to contain it).Distance to the conveyed edge, in some cases, may be further than the closest rout edge. Proper definition of rout or profile is essential to the accuracy of the check. Does not report components with attribute Ignore During Spacing Analysis. Does not report copper features with attribute Copper Feature Ignore.

  • Toeprint to Non-Conveyed Edge 

Reports distances between toeprints/exposed toeprints of components and non-conveyed edges (edges perpendicular to the SMT process) in the rout layer. The test checks distances to a bounding box of the board (the smallest rectangle to contain it).Distance to the non-conveyed edge, in some cases, may be further than the closest rout edge. Proper definition of rout or profile is essential to the accuracy of the check. Does not report components with attribute Ignore During Spacing Analysis. Does not report copper features with attribute Copper Feature Ignore.

  • Exposed Via to Exposed Toeprint 

Vias may create a solder bridge with the toeprint of a component.

  • Exposed Via to Other Net Exposed Toeprint 

Vias may create a solder bridge with the toeprint of a component. Vias and toeprints belonging to different nets require different spacing rules than those of the same net.

  • Via to Toeprint Masked Trace

Avoid bridging of solderpaste between the toeprint and the via.

  • Irregular Exposed Toeprint 

Solder mask exposure of toeprints provides electrical contact between the toeprint pad and component pin. Irregular solder mask exposure may indicate a design problem of insufficient exposure.

  • Testpoints/Via Clusters 

Vias and testpoints tend to bridge (flow solder process) when they are arranged as a cluster.

  • Hole in SMD 

Reports the number of drills in an SMD pad (excluding blind and buried vias). SMD pads have both attributes SMD Pad and Pad Usage=toeprint.

  • Non-Uniform SMD Pad Size 

Excessive difference in pad size can cause a corresponding difference in temperature.

  • SMD Size 

Purpose: To detect SMD pads that are too small for differing component types.

  • Trace Width / Pad Perimeter (%) 

If both toeprints of a discrete component are not firmly attached to the board, one could disconnect during the assembly process and result in the component standing on its end (Tombstoning).

  • Toeprint Covered by Surface (%) 

If both toeprints of a discrete component are not firmly attached to the board, one could disconnect during the assembly process and result in the component standing on its end (Tombstoning).

  • Discrete Gap

The gap between the toeprints of small discrete components is critical to many aspects of the assembly process.

  • Multiple Trace Connection 

Purpose: To identify components where there are more than one trace connected to a toeprint. This is particularly important for BGA components.

  • Connection Width 

Some types of components require traces of specific widths to be connected to their toeprint pads.

  • Exposed Connection 

For some component types, even if the toeprint pad is exposed by the solder mask pad, the trace itself should not be exposed.

  • Wide Side Connection 

Purpose: To identify component types with long, narrow toeprint pads, that should have their traces connected to the narrow side of the toeprint.

  • Diagonal Connection

Purpose: To identify components types which should not have traces connected to toeprint pads diagonally.

  • Misregistered Connection 

Purpose: To identify components types which should always have traces aligned (registered) with their pad’s axis.

  • Irregular Connection 

Purpose: To identify components types whose trace connections cannot be checked.