Choosing between SMD and THT for your network transformer affects assembly process, mechanical reliability, and serviceability. Here's the complete technical breakdown.
Package Overview
SMD (Surface Mount Device):
Mounting: Soldered to board surface (reflow)
Footprint: Pads only, no drilled holes required
Assembly: Automated pick-and-place + reflow oven
Typical size: 8-pin (10/100) or 16-pin (Gigabit) SOIC/SOP
THT (Through-Hole Technology):
Mounting: Leads through drilled/plated holes (wave or hand solder)
Footprint: Plated through-holes + body clearance
Assembly: AI machine or hand-insertion + wave/selective solder
Typical size: DIP or SIP, 2.54mm lead pitch
Mechanical Strength Comparison
Joint type Pull strength Shear strength Vibration rating
────────────────────────────────────────────────────────────────────────
SMD solder pad Low–Moderate Low IPC Class 1–2
THT plated hole High High IPC Class 2–3
THT joints are anchored through the board. Under sustained vibration (IEC 60068-2-6) or mechanical shock (IEC 60068-2-27), THT joints outperform SMD across all standard test profiles.
Assembly Process Requirements
assembly_requirements = {
"SMD": {
"process": "Screen print → Pick & Place → Reflow",
"equipment": ["stencil printer", "pick-and-place", "reflow oven"],
"volume": "Best at medium–high volume",
"prototype": "Requires SMT equipment (or hot plate/hot air)",
"rework": "Hot air station + specialized tools"
},
"THT": {
"process": "Insert → Wave solder / Hand solder",
"equipment": ["wave solder machine", "OR soldering iron only"],
"volume": "Viable at any volume; higher cost at scale",
"prototype": "Hand-solderable with standard iron",
"rework": "Standard soldering iron + solder pump"
}
}
PCB Layout Impact
Parameter SMD THT
──────────────────────────────────────────────────────────────
Board real estate Low (surface only) Higher (hole + keepout)
Component density High Lower
Double-sided loading Yes (both sides) Limited (hole access needed)
Minimum footprint ~5×5mm (10/100 8-pin) ~12×8mm (DIP equivalent)
Height profile Low (<4mm typical) Higher (leads + body)
Lead inductance Near zero Small (~1–3nH per lead)
Application Selection Guide
Application Recommended Package
──────────────────────────────────────────────────────────
Consumer electronics / IoT SMD
PCBA modules (standard assembly) SMD
Industrial gateway (DIN rail) THT preferred
Transportation / automotive THT preferred
Medical device (long service life) THT (field serviceability)
Outdoor enclosure (thermal cycling) THT preferred
Engineering prototype (no SMT equip) THT
High-volume production (cost focus) SMD
Lead-Free Compliance Check
Both packages available in:
HASL-LF (Hot Air Solder Level, Lead-Free)
NiAu / ENIG (Electroless Nickel Immersion Gold)
Sn finish
Solder compatibility:
SMD reflow: SAC305 (Sn96.5/Ag3/Cu0.5), peak 245–260°C
THT wave: SAC305 or SN100C, pot temp 260–270°C
Verify: transformer body rated for reflow temperature if SMD
(should be ≥ 260°C peak, check Tmax in datasheet)
Mixed Technology Strategy
Common approach for ruggedized Ethernet ports:
RJ45 connector: THT → mechanical strength for plug cycles
Network transformer: SMD → signal performance, density
PHY chip: SMD → no THT option available
Assembly flow:
1. SMT → reflow (PHY + transformer)
2. THT → selective solder or hand (RJ45 connector)
Source
Voohu Technology (www.voohuele.com) — network transformers in both SMD and THT packages, 10/100 and Gigabit, standard and PoE-rated. MOQ 50pcs, DHL 3–5 days.
Top comments (0)