pcb 101 - how to build a circuit board

DELIVERING QUALITY SINCE 1952.

How to Build a Circuit BoardPCB 101

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America's Oldest,A History of Innovation

Privately held company, established in 1952.

Estimated 2013: Sales: US$40 Million

100+ Employees Worldwide (70 – North America, 30 – Asia, 3 – Europe)

Design and manufacture customized, built-to-print, performance-critical products for all sectors of the electronics industry.

Leading provider of printed circuit boards, membrane switches, graphic overlays, silicone rubber products, electronic heaters, fans, motors and custom battery packs.

Integrated supply chain management solutions to handle the complexity of today’s global marketplace while making sure that every order is being manufactured at the “right” factory.

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Global Operations

Significant Investment in People and Facilities across the globe.

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Our Customers - The Top GlobalOEM’s In Growth Industries

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Our Products

Battery Packs Flex & Rigid-Flex PCB’s User Interfaces

Fans & Motors Cable Assemblies Printed Circuit Boards

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PCB Design and Layout

Our Capabilities Encompass The Full Design Flow From Start To Finish Including:

Micro BGA / Micro Via / Blind and Buried ViasRules Driven DesignsSchematic CaptureLibrary DevelopmentDatabase Construction and VerificationSignal Integrity/Design VerificationEMI CheckingFull Document Package CreationElectrical Engineering Expertise

We are fully licensed and utilize industry leading tools, including Cadence Allegro, Mentor Expedition, Mentor's PADS, Altium, Valor for DFM Analysis.

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Customer Supplied Data

– CAD• ODB++, Gerber, Gerber 274X• Netlist (IPC-D-356)

– Drawing Package• Fabrication drawing• Readme File• Specifications

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Cam Deliverables– Conversion of Customer Supplied Data to Tooling

Panelization– Optimized manufacturing Panel– Customer defined sub-panels or arrays

Artwork– Inner Layer– Outer Layer– Soldermask– Legend

Drill and Rout Programs– Excellon format ASCII

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Engineering Strategy– Epec’s Front End Engineering Department uses state of the art software to identify

and reduce or eliminate unnecessary manufacturing costs.

EpecDFx - Perfecting the DFM Process– EpecDFx goes beyond DFM (Design for Manufacturability)

• Design for cost• Design for functionality

– ALL jobs are processed through EpecDFx checking for:• Shorts• Opens• Line widths• Spacing issues• Mask problems• Legend problems• Inner layer plane problems• Controlled impedance• Unused pads (and removal of same)

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Cores/Laminate– A thin laminate material (usually under .250” thick) consisting of a glass epoxy

substrate clad with copper on both sides.– The size of the core is larger than the finished size of the board.

Copper Foil

Laminate

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Laminate: CEM-1Low cost – Single Sided Industry standard for low cost single sided PWB.

– Material of choice for low cost, single sided PWB applications– Suitable for low to moderate board rigidity requirements (lowest rigidity of these

three laminates)– May not be suitable in environments where moisture absorption is of high concern

CEM-1: A 5-ply composite composedof one ply of epoxy-resin impregnatedglass cloth above and below a 3-plyepoxy-resin coated paper core.

COPPER FOIL

EPOXY-RESIN GLASS CLOTH

3-PLY KRAFT PAPER CREATING ANEPOXY-RESIN COATED PAPER CORE

EPOXY-RESIN GLASS CLOTH

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Laminate: FR-4– Industry Standard Rigid PWB Laminate– FR-4 is truly the most generic laminate– Many different manufacturers offer products with different characteristics

FR-4: Eight weaves of fiberglasscloth laminated together with anepoxy resin. (60% Glass / 40% Resin)

COPPER FOIL

EIGHT WEAVES OF FIBERGLASSCLOTH LAMINATED TOGETHER WITH AN EPOXY RESIN

COPPER FOIL

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Dry Film Resist Coat– A light sensitive film is applied by heat and pressure to the copper surfaces of the

core

Photo Tools & Artwork– These are placed on the film coated surfaces of the core– Artwork patterns are customer designs containing circuit and land patterns specific

to that part number– Each surface has its own artwork pattern

Etch Photoresist

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Expose– Panels are exposed to ultra-violet light– Clear areas allow light to pass through and polymerize (harden) the film resist thus

creating a latent image of the circuit pattern

Develop– The exposed core is passed through a chemical solution removing the resist from

areas not hardened (polymerized)

Artwork

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Etch– Copper is chemically removed from the core in all areas not covered by film resist– This creates a discrete copper pattern– Core surface now shows through in areas where copper was etched away

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Strip Resist– The developed dry film resist is now chemically removed from the panel– Copper remains on the panel only in the patterns described by artwork

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Oxide Coating– Copper is chemically treated to “rough-up” surface– Rough surface improves adhesion to prepreg during the lamination cycle– Oxide is typically black, though other types exist, i.e. Brown and Red

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Multilayer Lamination– Materials Needed:

• Copper Foil

• Prepreg

• Cores

Prepreg– Multilayer “glue”– Fiberglass cloth preimpregnated with partially cured epoxy resin– Also known as B-stage

Copper Foil– Typically in sheets at ½ oz. or 1 oz. per square foot in weight (.0007 and .0014

inches nominal thickness respectively)

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Laminated Blank– Inner Layer Core, Copper Foil and Prepreg are bonded together under heat and

pressure, usually in a vacuum, during the lamination process– Prepreg resin is activated and “melts”, flowing across the layer to create a bond.– Half-sheets are produced during this step– Half-sheets are then cut or fabricated (fabed) into panel size

Primary Drilling– Double Sided/Single Sided Start here

• Holes are drilled through a stack of panels (usually 2 to 3 high)

• Drilled holes are typically .005” larger than finished plated through hole size

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Drill– Holes are CNC drilled to specific coordinates from the data supplied after it is

formatted

Inner Layer

Laminate

Copper Foil

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Multilayer Stack-up(Cross Section)


4 Layer

6 Layer

8 Layer

Copper Foil

Double sided core

B-stage Prepreg

(Bonding Sheets)

(.5, 1, 2, ... ounces)

(.028 for 4 layer)

(.014 for 6 layer)

(.008 for 8 layer)

Copper weight up to 3 ounces

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Deburr & Clean– A mechanical process where copper burs are removed from the panel– All debris is cleaned from drill holes

Desmear– Applies to multilayer boards only– A chemical process where the coating of resin, produced by the heat of drilling, is

removed from the hole wall

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Copper Deposition– Also called electroless copper– A thin coating is chemically deposited on the surface of the panel and hole walls– This creates a metallic base for subsequent electroplating operations– Typically thickness is 80-100 millionths of an inch

ElectrolessCopper

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Dry Film Photo Resist Coat– The panel is pre-cleaned– Light sensitive film is applied, using heat and pressure, to the copper surfaces of

the laminated “blank”– Film also covers, or tents, all drilled holes

Inner Layer

Laminate

Copper Foil

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Expose & Develop– The panel is then exposed and developed– Similar to the inner layer process for the core– Holes that are to be plated have tents developed off

Photoresist

Artwork

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Copper Pattern Plate– Also called electroplating– Additional copper is electrically plated onto the exposed electroless copper

surfaces– Copper thickness is approximately 1 mil– Tin is also plated onto all copper surfaces– Typical tin thickness is .3 - .5 mils

ElectroplatedCopper

Resist Metal (tin)

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Etch– Copper is now removed any place not covered by tin– The tin acts as an etch resist– Traces and pads, as defined by the artwork, are now left on the surface of the panel

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Strip Resist– The developed dry film resist is now chemically removed from the panel– Tents that were placed have prevented plating to occur in holes designed to be

non-plated

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Solder Mask & Cure– A Liquid Photo Imagable mask, is applied to each surface and dried to the touch,

but not cured– Artwork is applied and exposed– Panel is developed, leaving mask in pattern described by artwork– Panels are cure baked– Mask protects panels from contamination and handling damage– Solder mask is a non-conductive material– Laminate is a natural color, solder

mask gives the circuit board itsfinal color, typically green

Solder Mask

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Hot Air Solder Leveling (HASL)– Panels are processed thru a bath of molten solder, covering all exposed copper

surfaces

– High pressure hot air, directed at both sides of the panel simultaneously, removes excess solder from the holes and surfaces

– While HASL is still the most commonPCB surface finish, many otheroptions exist that will allow ourcustomers to meet their endproduct needs.

Solder

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Surface Finishes

– RoHS Compliant:• Organic Solder Preservation (OSP)• Single and Multi-Pass• Lead-free HASL• Nickel Plate• Nickel/Gold• Palladium – Nickel• Immersion Tin• Immersion Silver

– Not RoHS Compliant:• Hot Air Solder Leveling (HASL)

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OSP Surface Finishes

– Single-Pass – single soldering operation (or heat cycle)– Multi-Pass - able to survive multiple heat excursions for SMT applications– Coating is molecular in thickness and is compatible with most flux systems,

including “no wash” systems– DOES NOT CONTAIN LEAD!

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Lead Free HASL

– There are several types• SN100 (most common in China)

– Tin – trace of Copper < 0.7%

• SAC305 – Limited availability

– Tin – 3.0% Silver - .05% Copper

– PCB is conveyed through the flux station, then through the solder bath and finally through a set of air knives that remove (level) excess solder

– Thickness varies - Generally somewhat thinner than regular HASL:• From .000100” to .001500”

– Lead Free HASL provides a solderable surface with most flux systems and is also suitable for most surface mount applications

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Ni / Au Plating

– Electroplated Deposit• SMOBC – soldermask used as plating resist• We will only plate Ni/Au after etching – we will not use Ni/Au as an

etching resist• All circuits or features which will be electrically connected with plating buss (tie

bars)• Thickness for Gold: .000005” to .000050”

– ENIG – Electroless Nickel/Immersion Gold• Bussing (tie bars) not required• Max. Thickness for Gold: .000002” to .000005”

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Immersion Tin (Also known as White Tin)

– Excellent Co-planarity– Shelf life equal to or exceeds HASL– Will solder after multiple heat cycles – Solder paste, reflow, glue dot

and wave soldering– Less dimensional stress than with HASL– No special handling required

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Immersion Silver

– Totally flat topography– More solderable than copper– Does not require special handling like OSP (white gloves, etc.)– Shelf life is 6-12 months depending on storage conditions– Can withstand 5 temperature cycles

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Hot Air Leveling (HAL, HASL)

63/37 Solder Coating

– PCB is conveyed through the flux station, then through the solder bath and finally through a set of air knives that remove (level) excess solder

– Thickness varies:• From .000100” to .001500”

– HASL provides a solderable surface for all flux systems and is also suitable for surface mounted applications

– Still the most common protective coating used in PCB manufacturing

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Legend & Cure– Ink is silkscreened onto each side of the

panel as described by customer artwork– The printing details component placement

and other surfaces details desired bythe customer

– Panels are baked to cure the ink

Legend & SMTLegends can create problems for the PCB manufacturers.– Many designers put a box completely surrounding SMT pads to indicate component

placement– Often the tolerances required to screen print legend are not considered. Avoid

narrow fonts, text height less than .040” and trace width below .006”– Ask your designer to provide adequate clearances around SMT pads

Nomenclature

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Legend Placement Around SMD Pads

Good

Too Tight

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Fabrication / Routing

– The board is cut to size– Also known as routing, scoring, punching or profiling– Chamfers and slots are also added during this step

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V-Groove ScoringEngineers see scoring as a way to save. It does save from a material utilization basis, but there are tradeoffs. Tolerances must be relaxed on the finished piece part to allow for these tolerances. Furthermore, scoring has one of the highest fallout rates of any process in manufacturing.

Score line to Score line +/-.005”

Score line to holes +/-.007”

Score line to Artwork .015 - .020

Finished part tolerance +.015/-.010

Web Remaining +/-.005”

CEM-1 .030”

CEM-3 .030”

FR-4 .015”

HIGH Tg FR-4 .012”

Typical Web remaining for each laminate

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V-Groove ScoringScoring: Usually defined as “Web remaining.” This defines the amount of material remaining. The cutter has a 30 degree included angle. (45 and 60 degree cutters available)

* Note how the width of the score line changes with the depth of cut.

0.01

0

0.01

5

0.03

0

0.008 0.013

0.012Typical for CEM1 and CEM-3

Typical for FR-4

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Copper Weight vs. Minimum Spaces

– 1 ounce copper - .008” between adjacent features– 2 ounce copper - .010” between adjacent features– 3 ounce copper - .012” between adjacent features– 4 ounce copper - .015” between adjacent features– 6 ounce copper - .020” between adjacent features

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Electrical Test

– Board is tested for electrical integrity, and if required, impedance– Data can be directly loaded from CAM to test machines in some cases– Most tests are feasible. Repairs of shorts and opens are also done at this point– Smaller lots tested on a flying probe, larger volume on a bed of nails test fixture– IPC Netlist is used if supplied by the Customer

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Functions Performed Throughout the Process:

– AOI• Automatic Optical Inspection• Inner layers and outer layers are tested against downloaded CAM data for

integrity, and against design rules• If allowed and feasible, repairs are made at this point• Data is fed back to

appropriate departmentsto correct processproblems

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– Reliability Lab• In-house capability to test for compliance to many customer and industry

requirements• Environmental Cycling, Ionic Contamination, Surface Insulation Resistance are

a few tests performed.• Data is fed back to departments and customers as required

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– SPC• Statistical Process Control• Method used both on and off-line to determine if process and product is

performing as expected• ONLY reliable method to make process changes• Often required by customers

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PCB Design Concerns

– Hole Size• >10 Mils drilled standard• 8 – 9 Mils, leading edge• 5 Mils, bleeding edge• Note: Drilled hole size typically

is .003”-.005’ larger than FHS

– Pad Size• 10 Mils over drilled hole

diameter standard• 8 Mils leading edge• PWG/GRD Clearance – 20 mils

over drill

PCB Design Concerns

– Line/Space• 5/5 standard• 3/3 leading edge

– Aspect Ratio• 8:1 standard

– 0.080” min hole size for 0.062”

• 12:1 leading edge– 0.005” hole for 0.062”

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PCB Manufacturing Concerns

4 Layer Off Center Construction

Warpage Issues Meets flatness specification

.024”

.024”

.006”

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Manufacturing / Design Concerns

Plating– External copper thieving is recommended to be added to low-density areas to even

out copper distribution. Typical thieving pattern is .030” squares on .050” centers.– The absence of copper thieving result in high, or over plating of isolated features,

typically differential pairs. It can also cause pitted appearance on fiducial pads, which will cause assembly problems.

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Panelization

– PWB’s are manufactured on standardpanel sizes

– Cost is a factor of the number of individualcards on a production panel

– Impedance/Mil coupons, if required,are placed in the production panelMay effect panelization yield, i.e. $$

– Industry standard panel size is 18” x 24”– General rule:

• 0.750” border all 4 edges

• 0.100” spacing between images

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Sample Fabrication Drawings/Notes

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Price Considerations

– Low Cost Factors• Complex Routing/Scoring

• Edge Routing

• >0.093” Thick PWB’s

• <0.030” Thick PWB’s

• High Tg vs. low Tg Materials

– Medium Cost Factors • High Drill Hole Quantity

• Plated hole tolerance less than +/- 0.003”

• Edge Plating

• Drilled holes <0.010”

– High Cost Factors • Advanced Technologies

• Buried Vias

• Layer Count

• Material Utilization

• Selective Plating

• Line Width and Space

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Industry’s Leading Online Tools

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World Class Quality Assurance& Engineering

US Based QA Capabilities Include:– Full Cross Section/Microsection Reporting and

Ionic Testing Equipment– X-Ray Fisherscope for all Metal Thickness &

Purity Measurement on every lot.– Scienscope DMP-1000 stereo zoom

microscope with digital picture capability up to 100x

– Vision Engineering Mantis Elite for 10X full range visual inspection.

– World Class Electronics Test Lab Epec’s superior on-time delivery rates are the result of our significant, dedicated engineering resources and processes.

– Perform all DRC, DFM, Graphic Art and Engineering reviews at our Engineering Center outside of Boston, MA

– Documentation of all manufacturing and detailed planning processes, for all special requirements,

– Consistent documentation and tooling at all manufacturing locations to ensure seamless prototype through production manufacturing.

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Design Centers &Technical Support

Battery Pack & Power Management – Denver, CO User Interfaces – Largo, FL Fans & Motors – Wales, UK PCB’s – New Bedford, MA & Shenzhen, China Flex & Rigid Flex – Toronto, Canada Cable Assemblies – New Bedford, MA Heaters & Sensors – Boston, MA

Our Engineering and Design teams are ready to help our customers create world class and cost effective product solutions.

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Inventory Management

Customer requirements are always unique and customized, therefore our inventory management system must accommodate for this type of environment.

We Offer:

– Kanban

– Consignment

– JIT Programs

– Blanket Orders

– Customer Fulfillment

– Bonded Warehousing

– Kitting

– Safety Stock

– Other flexible solutions

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The Difference is Quality and Delivery

1. Quicker Delivery - Epec's technology infrastructure and people, including the Asian and US based operations, manufacturing and engineering teams, enable jobs to get started the same day the order is received with no delays.

2. Accurate Information - Epec's proven supply chain and manufacturing experience allows accurate daily Work In Process reporting so customers can receive immediate order status information.

3. Better Quality - Epec ensures higher levels of quality through actual investment in all of our processes. Whether it is our 10+ people strong quality organization in Asia, equiping our tech centers with the latest tech gear to test parts, or our continuous improvement auditing process, real investment is made to ensure quality.

4. Flexibility - Each of our manufacturing facilities have been selected for theirbest-in-class niche product and delivery and techology solutions, ensuring our optimal facility is building every order.

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If you require additional information please contact us with any questions or requests.

North American Headquarters174 Duchaine Blvd.New Bedford, MA 02745Tel: (508) 995-5171Fax: (508) 998-8694

Contact Us By Email:Sales [email protected] [email protected] [email protected]

Visit Our Website For More Informationwww.epectec.com

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pcb 101 - how to build a circuit board

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