1. WHAT IPC IS
IPC (Association Connecting Electronics Industries) publishes the most widely used
PCB design, fabrication, assembly, and inspection standards. Official IPC
documents are paid, but the concepts described here reflect common industry
practice.
Important IPC documents (names only): IPC-2221 – Generic PCB design rules
IPC-2222 – Rigid board design
IPC-7351 – SMT land pattern design
IPC-6012 – Rigid PCB performance and fabrication
IPC-A-600 – Bare PCB acceptability
IPC-A-610 – Assembled PCB acceptability
J-STD-001 – Soldering requirements
1. IPC PRODUCT CLASSES
Class 1: General Electronic Products
Used for consumer or disposable products where cosmetic defects are acceptable
if function works.
Class 2: Dedicated Service Products
Used for industrial or commercial equipment where extended life is required.
Class 3: High-Reliability Products
Used for medical, aerospace, military, or safety-critical electronics. Tightest
tolerances.
Higher class means higher cost, tighter inspection, larger margins.
1. CONDUCTOR WIDTH AND CURRENT (IPC-2221 / IPC-2152 CONCEPT)
Trace width depends on: Current carried
Allowed temperature rise
Copper thickness
Internal vs external layer
External traces cool better and can be narrower than internal traces for the same
current.
Avoid long, narrow power traces. Use pours or multiple vias.
1. TRACE SPACING AND CLEARANCE
Spacing prevents: Short circuits
Arcing at higher voltages
Manufacturing defects
Spacing depends on: Voltage
Environmental conditions
Product class
Board coating
High-voltage designs must exceed minimum values.
1. ANNULAR RING
The annular ring is the copper left around a drilled hole after drilling.
Problems occur if: The drill hits off-center
Copper ring breaks
Barrel connects poorly
Larger annular rings increase yield and reliability, especially for Class 3.
1. PLATED THROUGH HOLES (PTH)
A plated through hole must have continuous copper from top to bottom pads.
Common defects: Thin plating
Voids in the barrel
Cracks from thermal cycling
Barrel cracking is a major reliability failure in harsh environments.
1. VIAS
Via types: Through via – goes through entire board
Blind via – outer layer to inner
Buried via – inner to inner
Smaller vias save space but reduce reliability. Filled and capped vias improve
assembly quality.
1. SOLDER MASK
Solder mask: Prevents solder bridging
Protects copper
Improves reliability
Good practices: Mask must not cover pads
Maintain solder mask dams between fine-pitch pads
Tent vias when possible
1. SILKSCREEN (LEGEND)
Silkscreen is used for reference designators, polarity, and logos.
Rules: Do not print on pads
Keep text readable after soldering
Mark pin 1 and polarity clearly
1. IPC-7351 LAND PATTERNS (FOOTPRINTS)
Footprints must allow proper solder fillets.
Key areas: Toe fillet (front of pad)
Heel fillet (under component)
Side fillet
Incorrect footprints cause tombstoning, weak joints, or opens.
1. SOLDER JOINT ACCEPTABILITY (IPC-A-610 STYLE)
Acceptable solder joint: Smooth surface
Concave fillet
Good wetting to pad and lead
Unacceptable conditions: Cold (grainy) solder
Excess solder
Insufficient wetting
Bridges
1. COPPER BALANCE AND BOARD FLATNESS
Uneven copper causes: Board warping
Assembly defects
Fine-pitch failures
Balance copper areas across layers whenever possible.
1. COMMON BARE-BOARD DEFECTS (IPC-A-600 STYLE)
Over-etch or under-etch
Nicks in traces
Delamination
Blisters
Measling
Broken annular rings
Higher IPC class allows fewer defects.
1. DESIGN FOR MANUFACTURING (DFM)
General rules: Avoid tiny drills
Use standard drill sizes
Avoid sharp angles (<45°)
Keep consistent trace widths
Document board class clearly
1. QUICK DESIGN CHECKLIST
Correct IPC class defined
Trace widths sufficient
Spacing adequate
Footprints verified
Vias manufacturable
Mask openings correct
Silkscreen readable
1. LEGAL NOTICE
This handbook: Is an original educational summary
Does not reproduce IPC text
Is not an official IPC document
Is safe to share internally or for training
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