Dana on Data: DFM Issue Reduction—Company-specific PCB Acceptance Specifications

PCB data packages commonly generate fabricator DFM feedback questions that require resolution. Resolving these issues delays the manufacturing cycle time until the issues are resolved. There are many methods and techniques to reduce the DFM issues, such as working with the fabricator to review proposed stackup materials and impedance structures early in the design cycle. Another common method is to generate a company specific acceptance specification that provides requirements that are not covered in referenced IPC specifications and include negotiated DFM issue resolutions.

There are two generic sections in this document:

  1. Referenced IPC specification modifications

  2. Global approved deviation approvals

Let’s use the commonly referenced IPC-6012 “Qualification and Performance Specification for Rigid Printed Boards” specification as an example on where OEMs will modify the requirements to conform to their application.

IPC Specification Modifications

These company requirements will add, delete, or modify information contained in specific sections. Here are a few examples:

Section 1.2.1 Supporting Documentation [Additional requirements]

a) If Gerber data is provided, it is for reference only and may not be used for fabrication of the PCB. Only IPC-2581 design data shall be used for PCB fabrication.

b) All supplied documentation and data are company confidential, remain the property of [The Company], and shall be returned to [The Company], or their agent, upon request.

Section 1.3.1.1 Requirement Deviations [Modification]

Requested deviations or modifications to the provided documentation or design data shall be approved in writing by an authorized representative prior to the initiation of PCB fabrication, unless otherwise specified herein.

Section 3.2.11 Hole Fill Insulation Material [Modification]

Electrical insulation material used for hole-fill for metal core boards shall be determined by the fabricator and approved in writing prior to use.

Section 3.2.12 Heatsink Planes, External [Modification]

Deviations to these requirements shall be approved in writing before fabrication starts.

Section 3.3.5.4 Marking Types and Location [Additional requirements]

a)  Markings shall be either etched or as legend ink.

b) Markings shall be placed on the solder side or layer n side, where n is greatest numbered layer at locations indicated on the fabrication drawing, or IPC-2581 files as applicable.

c) Markings shall include, but not be limited to the following:

  1. Manufacturer’s UL Recognized Component Marking

  2. UL Flammability Rating

  3. UL 796 Direct Support Rating as indicated in the design documentation

  4. Date Code and Lot Code are mandatory

  5. Date Code shall be YYWW format

  6. The Date Code year (YY) shall use the calendar year

  7. Lot Code shall be traceable to the supplier fabrication records

Section 3.7 Solder Mask Requirements [Additional requirements]

a) The solder mask color and gloss shall be specified in the documentation.

b) Liquid Photoimageable (LPI) solder mask shall be used as the default.

c) Solder mask over bare copper (SMOBC) shall be used unless otherwise specified.

Global Approved Deviation Approvals

These items are previously documented data DFM issues that have been raised by one or more fabricators. There are many commonly asked DFM issues. These may be termed “Globally Approved Edits” as they apply to all design packages. The advantage of this list is that future design packages and new suppliers won’t have to ask these questions because you have already provided the answers. This solves the complaint, “Quit asking the same question over and over again.” Here are a few examples:

“The following modifications, as required, to the provided design data do not require pre-approval by [The Company]. The following edits, other than scaling, shall be documented in the DFM report when sent to the technical contact for approval of other items.”

a)  Scaling: Incorporate scaling factors to compensate for material shrinkage/expansion in the PCB fabrication process.

b)  Solder Mask: Solder mask apertures specified in the data, directly adjacent to exposed conductive features, shall be modified to maintain proper clearance to the exposed conductors.

c)  Legend Marking:  Legend shall be trimmed or moved from a solder resist opening to avoid printing on exposed conductors.

d)  Non-Functional Pads Removal: Non-functional pads on internal signal layers may be removed except for PTH’s greater than 2.5mm [0.098"].

e)  Impedance Traces: Dielectric thickness may be modified to meet impedance requirements.

f)  Anti-pad Size: May be modified to meet annular ring requirement.

g) Pad Size: May be modified to meet annular ring requirement.

h) PCB Corners: Modify to add a radius to not damage shipping packaging.

i) Date Code Format: Shall be selected by fabricator.

j) Tear Drops: May be added to pad to trace connections as required.

k) Duplicate Holes: Remove all occurrences. If the holes are different sizes, the smaller size shall be deleted.

l) Drill Data: Modify to align to pads for through hole mounted components.

m) Copper Thieving: To improve metal distribution and uniformity across an internal signal or outer layer, copper thieving features may be added to layers, provided the specified impedance and safety isolation requirements are unaffected.

  1. The minimum spacing between a thieving, or dummy pad, feature and any conductor shall be 0.100 inches (100 mils) for both internal and external layers

  2. The supplier shall provide a graphic representation with size and spacing of thieving that has been added for written approval

The above global deviation examples should be reviewed to ensure that the design performance requirements are met. High speed digital design signal integrity loss and noise budgets are becoming more sensitive to trace and via editing and thus may not allow all approved global edits.

The goal of transferring the design data for manufacturing should be to eliminate DFM issues that may affect the production cycle time, quality or PCB reliability.

Dana Korf is the principal consultant at Korf Consultancy LLC. 

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2022

Dana on Data: DFM Issue Reduction—Company-specific PCB Acceptance Specifications

05-26-2022

PCB data packages commonly generate fabricator DFM feedback questions that require resolution. Resolving these issues delays the manufacturing cycle time until the issues are resolved. There are many methods and techniques to reduce the DFM issues, such as working with the fabricator to review proposed stackup materials and impedance structures early in the design cycle. Another common method is to generate a company specific acceptance specification that provides requirements that are not covered in referenced IPC specifications and include negotiated DFM issue resolutions.

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Dana on Data: Is the Customer Always Right?

03-03-2022

Is the customer always right when it comes to customer PCB design data? Fabricators would be taking the design data and building the supplied data verbatim if this was true. The fabricator would only need to compensate conductors to account for etching processes and map finished hole sizes to drill sizes.

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2021

Dana on Data: Understanding Mechanical Drill Size Capability and Cost

09-29-2021

Fabricator capabilities are generally initially provided on a one-page summary as part of the general marketing presentation. The technical values that are presented provide the “check mark” information so the potential customer can determine if the fabricators capability is greater than the design requirements. Often, this is the only method used for design rule knowledge transfer.

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Dana on Data: The Critical Importance of the Fab Product Engineer

07-29-2021

Billions of dollars are spent yearly on CAD and CAM software to produce complex PCB designs and fabricate PCBs. The final technical manufacturing decisions generally are made by one person for each design. This is the PCB fabricator product engineer. But I don’t think most design, procurement, or NPI teams understand how critical this person is to the data transfer success and liability protection.

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Dana on Data: Effective Front-end Engineering External KPIs

05-13-2021

PCB fabricator front-end engineering departments are always under great pressure to be kept small, generate production tooling instantaneously from customer data and never, ever, make a mistake. Key performance indicators (KPI’s) emphasis internal process improvements and are generally simple in nature, such as jobs/person/day and scrap dollars/month.

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Dana on Data: Factory 4.0 NPI Compatible Industry Specification Format

03-11-2021

IPC APEX EXPO’s emphasis on the Connected Factory Initiative based on CFX and IPC-2581 is underway in a virtual mode this month. One area that has not been addressed is the automation of industry technical specifications from organizations like IPC, ASTM, UL, IEC, etc.

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Dana on Data: Factory 4.0 NPI Data Transfer Improvements

01-14-2021

The recently released IPC Connected Factory Initiative scope is similar to other Factory 4.0 models with the same glaring omission: They all seems to assume that the incoming design data can’t be used as-is and must be reviewed and potentially manually modified prior to manufacturing release.

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2020

Dana on Data: Reducing PCB Specification Interpretation Issues

11-12-2020

The PCB industry has accepted a low-quality level of provided documentation from its customers for the past several decades. In this column, Dana Korf reviews one common fabrication print note and asks, “How do you interpret this note?”

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Dana on Data: A Team Method to Reduce Fabricator Engineering Questions

09-03-2020

Hundreds of PCB designs are released to be quoted or fabricated every day around the world, and most will have engineering questions or technical queries generated once the data package has been received and analyzed. Dana Korf outlines seven fundamental steps based on Lean/Six Sigma concepts to reduce data transfer issues.

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Dana on Data: How Can the PCB Industry Improve From COVID-19 Responses?

07-16-2020

In response to the COVID-19 pandemic, the world transformed a very slow medical approval process into the equivalent of a concurrent NPI process by challenging some of the golden rules. Dana Korf shares his thoughts on four areas the PCB industry can re-evaluate and improve.

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Dana on Data: The Importance of PCB Technology Roadmaps

05-14-2020

Peter Drucker once said, “Trying to predict the future is like trying to drive down a country road at night with no lights while looking out the back window.” Dana Korf explains how it is critical that PCB fabricator technology roadmaps and capacity planning align with their customers’ product development and volume requirements to ensure that optimum cost, reliability, and performance goals are achieved.

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Dana on Data: Automating DFX Transfer and Analysis Using IPC-2581C

03-19-2020

We are inching closer to a world where a complete intelligent PCB data transfer is realized. The IPC 2-16 Digital Product Model Exchange (DPMX) Subcommittee has just sent revision C out for IPC-2581 Consortium review with final industry approval targeted for this June. Dana Korf discusses the significant additions and their impact.

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Dana on Data: Creating IP-protected PCB Design Rules

01-09-2020

One of the primary reasons that data packages aren’t compatible is the fabricator/assembler does not provide a complete set of design rules out of concern of giving away their intellectual property (IP). Dana Korf explores the design rule development hierarchy as well as what should be included in an IP-protected design rule document.

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2019

Dana on Data: The DFM/Data Transfer Process Is Broken

11-14-2019

In a world that is showing great strides toward implementing a Factory 4.0 world, why can’t a design be passed from a designer to the fabricator without errors every time? Dana Korf emphasizes moving the responsibility up in the food chain, examines key design package error categories, and proposes creating a cultural change.

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New Column—Dana on Data: IPC-2581 Intelligent Bi-directional Data Flow

09-12-2019

The IPC Consortium is nearing completion of transferring notes on drawings and working with IPC on converting key IPC specifications into attributes that can be automatically loaded into CAD and CAM systems. This format is extendable to created automated company-specific acceptance files that can be automatically loaded into the CEM’s or fabricator’s engineering systems. IPC-2581 data format is being widely used globally and now needs to become the standard to reduce NPI cycle times by associating critical design information automatically to the physical features.

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