DFM

There are a lot of steps and processes going on during printed circuit board (PCB) manufacturing, and your contract manufacturer wants to make sure ahead of time that your PCB board won’t have any design for manufacturability (DFM) issues that could cause problems, like costly halts in production and wasted runs. PCB DFM checks can be performed by the PCB manufacturer to ensure your PCB is manufactured correctly, and improve your product’s reliability.

As a value-added service contributing to our PCB fabrication and assembly services, MADPCB provides free DFM check, also known as free DFM. PCB designers tend to know little about manufacturing and some points described in design file may not be totally compatible with manufacturing requirements. In DFM check process, our CAM engineer checks your original Gerber files for possible DFM issues. If any issues found, we will contact you immediately to give you modification suggestions. When the DFM issues solved, the boards will be put into fabrication through the PCB manufacturing process.

 

5 DFM Check Aspects

 

PCB DFM check is the first step in manufacturing your printed circuit boards (PCBs). As a PCB manufacturer, MADPCB always performs DFM check on 5 aspects, including Hole Checks, Signal and Mixed Layer Checks, Power or Ground Layer Checks, Solder Mask Checks, Silkscreen Checks. These DFM checks are based on design rules and manufacturing capabilities. You can go through the following for details of each DFM check aspect.

 

Hole Checks

The hole checks process is intended to find potential manufacturability defects in drill layers, including NPTHs and PTHs (thru via, buried and blind via layers) and create.

Drill Checks	Purpose
Hole Size	Provides a list of all PTHs, NPTHs & vias, all NPTHs that need 1st drills.
Hole Separation	Reports duplicated holes, touching holes and close holes.
Missing Holes	Reports missing drills for non-SMD (solder mask defined) pads
Extra Holes	Reports redundant drills that do not belong to any pads.
Power /Ground Shorts	Reports drills touching large copper nets of more than one power or ground layer.
NPTH to Route	Reports drills that have the tooling hole or mounting hole attributes, and NPTHs that are close to the route path.
Stubbed Vias	Reports cases of vias not connected to at least two copper layers.
Thermal Connection	Reports the absence of thermals for thru-hole pin drills and calculates the total copper area of thermal connections through all negative power, ground and mixed layers.

 

Signal and Mixed Layer Checks

 

In DFM checks, signal and mixed layer checks is intended to find potential manufacturability defects in signal layers and mixed layers and generate statistics. The action can operate on any layer, but is mainly intended for signal layers. It uses the layer itself and any NC (drill or route) layer which pierces it. The main checklist displayed in below table.

 

Signal and Mixed Layer Checks	Purposes
Spacing	Reports spacing violations between pads, circuits and nets, and between text to text, also shorts and spacing between different CAD nets &close distances between non-touching features on the same CAD or layer nets.
Drill	Reports distance violations between NPTHs/PTHs/Vias, and pads, circuits, annular rings and copper. Also reports missing pads.
Route	Reports distance violations between edge of route features and pads, circuits, etc.
Size	Reports size of pads, shaved lines, text, line neckdowns, arcs and shaved arcs.
Silver	Reports on silvers between lines and pads & between pads and pads. Silvers between a text feature & a functional pad will be reported, while silver between two features with the copper text attribute will be ignored.
Stubs	Reports unconnected line endpoints.

 

Power /Ground Checks

 

Power /Ground Checks are intended to find potential manufacturability defects in power, ground and mixed layers. It uses different algorithms to diagnose negative and positive power and ground layers. The main checklist is displayed in following table.

 

Power /Ground Checks	Purposes
Drill	Reports distance violation between NTPHs/PTHs/Vias to plane, copper, clearance and annular rings.
Silver	Reports silvers in negative and positive layers.
Route	Reports close spacing between copper/clearance and route features.
Thermal	Reports spoke (tie) widths and reducing of connectivity of thermal pads.
NFP Spacing	Reports spacing between NFPs (non-functional pads) and NFPs, NTPs and planes.
Plane Spacing	Reports spacing between features of different planes.
Keepin/Keepout Areas	Reports features inside or outside Keein or Keepout areas.
Plane Width	Reports insufficient width of copper between 2 drills connected to a copper plane.
Plane Connection	Reports disconnected areas of copper often used as reference planes that are left in a design could cause an unreferenced net, or a missing electrical connection.

 

Solder Mask Checks

 

Solder mask checks are intended to check solder mask layers for potential manufacturability defects. Solder mask layers are always assumed to be negative, that is, all positive features describe clearance or the absence of solder masks. This action also checks if solder paste has been deposited on all SMD pads. The action operates on a single solder mask layer per side at a time. If more that one SMD is selected, the action will not work. The main checklist is displayed in the following table.

 

Solder Mask Checks	Purposes
Drill	Reports close distance to solder mask openings of PTH/NPTH annular rings, and where NPTH touches mask.
Pads	Reports close distance to solder mask openings of all pads, including undrilled pads. It also reports on a special group, gaskets, which reports the width of solder mask overlap on features.
Coverage	Reports lines too close to clearance (that is, not adequately covered).
Route	Reports close distance between solder mask and route features.
Bridge	Reports close distance between solder mask and route features.
Silver	Reports silvers between solder mask clearance.
Missing	Reports missing clearances.
Spacing	Reports close spacing between clearance (wider than silver).
Extra	Reports solder mask features which lack copper pads, or do not intersect with copper.

 

Silkscreen Checks

 

Silkscreen checks are intended to find potential manufacturing defects in silkscreen layers and generate statistics. The check operates only on silkscreen layers as it relied on the job matrix to find related external copper, solder mask and drill layers against which to check. The main checklist is displayed in this table.

 

Silkscreen Checks	Purposes
Solder Mask Clearance	Reports close distances between silkscreen features and solder mask clearance.
SMD Clearance	Reports close distances between silkscreen features and SMD pads.
Pad Clearance	Reports close distances between silkscreen features and pads.
Hole Clearance	Reports close distance between silkscreen features and drills.
Route Clearance	Reports close distances between silkscreen features and route features.
Line Width	Reports line width violations and length to width ratio violations.
String Overlap	Reports the touching or intersection of silkscreen features of various string value.