PCB Assembly Process: Complete Step-by-Step Guide [2026]

After 15 years of working in electronics manufacturing, I’ve seen countless engineers struggle with the PCB assembly process—not because it’s impossibly complex, but because finding clear, practical information in one place can be a challenge. This guide breaks down every stage of the PCB assembly process, from design verification to final testing, giving you the knowledge to work more effectively with your assembly partner or optimize your in-house operations.

Whether you’re launching your first prototype or scaling to high-volume production, understanding the PCB assembly process helps you make better design decisions, catch potential issues early, and ultimately build more reliable products.

What is the PCB Assembly Process?

The PCB assembly process (often abbreviated as PCBA) transforms a bare printed circuit board into a functional electronic assembly by mounting and soldering components onto it. Think of it this way: the bare PCB is like an empty city—the roads and infrastructure exist, but nothing actually happens until you add buildings, utilities, and people. Similarly, a PCB only becomes useful when populated with resistors, capacitors, integrated circuits, and all the other components that make your circuit work.

The process encompasses two main technologies:

• Surface Mount Technology (SMT): Components are placed directly onto the board’s surface and soldered in a reflow oven
• Through-Hole Technology (THT): Component leads pass through holes drilled in the board and are soldered on the opposite side

Most modern assemblies use a combination of both—SMT for the majority of components and through-hole for items that need extra mechanical strength, like large connectors and power components.

Assembly Type	Best For	Speed	Component Size
SMT	High-density designs, miniaturization	Fastest	0201 packages and up
Through-Hole	Power components, connectors, mechanical stress	Moderate	Larger components
Mixed	Most production boards	Varies	Both types

Pre-Assembly: Design Verification (DFM/DFA)

Before any components touch your board, the assembly process actually begins with design verification. This step alone can save you thousands of dollars and weeks of delays.

Design for Manufacturability (DFM) Check

A DFM check examines your PCB layout against the manufacturer’s fabrication capabilities. The goal is catching potential manufacturing problems while they’re still cheap to fix—during design, not production.

Key DFM verification points include:

• Trace width and spacing: Minimum dimensions your fab house can reliably produce
• Drill sizes and aspect ratios: Ensuring holes can be properly plated
• Annular ring requirements: Adequate copper around drilled holes
• Solder mask clearances: Proper dam widths between pads
• Copper balance: Preventing warpage during thermal stress

Design for Assembly (DFA) Check

DFA focuses on whether your board can be efficiently assembled. This includes verifying:

• Component footprint accuracy: Matching pads to actual component dimensions
• Component spacing: Adequate clearance for pick-and-place equipment
• Orientation markings: Clear polarity indicators for diodes, ICs, and electrolytic capacitors
• Fiducial markers: Reference points for automated placement equipment
• Panel optimization: Efficient use of production panels

DFM vs DFA Comparison	Focus Area	Checks For
DFM	Fabrication	Trace width, drill sizes, clearances, copper weight
DFA	Assembly	Component placement, pad design, pick-and-place compatibility

Bill of Materials (BOM) Verification

Your BOM is the shopping list for assembly. Verification ensures:

• Part numbers match actual components
• Quantities are accurate
• Footprints correspond to specified packages
• Alternatives are identified for components with supply constraints

I’ve seen production runs delayed by weeks because someone specified a 0603 capacitor but the footprint was for an 0402. Catching this in DFM/DFA takes minutes; catching it during assembly costs days and money.

Step 1: Solder Paste Application

The PCB assembly process for SMT components begins with solder paste application. This gray, putty-like substance is a carefully formulated mixture of tiny solder spheres (typically 25-45 microns in diameter) suspended in flux.

The Stencil Printing Process

A precision-cut stainless steel stencil is aligned over the bare PCB. The stencil contains apertures (openings) that correspond exactly to the pads where components will be placed.

The process works like this:

1. The PCB is secured in a printing fixture
2. The stencil is aligned using fiducial markers
3. Solder paste is deposited on the stencil
4. A squeegee blade sweeps across, forcing paste through the apertures
5. The stencil lifts away, leaving precisely deposited paste on each pad

Solder Paste Composition

Modern lead-free solder paste typically uses SAC305 alloy:

Element	Percentage	Purpose
Tin (Sn)	96.5%	Primary bonding material
Silver (Ag)	3.0%	Improves wetting and joint strength
Copper (Cu)	0.5%	Reduces copper dissolution from pads

The flux component activates during heating to remove oxides and ensure proper wetting between the solder and the component leads.

Solder Paste Inspection (SPI)

Quality-focused assembly houses perform SPI immediately after printing. Using laser or camera-based systems, SPI measures:

• Paste volume on each pad
• Paste height consistency
• Registration accuracy (paste alignment to pads)
• Detection of bridging or insufficient deposits

Catching paste defects at this stage prevents downstream soldering failures and is far more cost-effective than finding issues after reflow.

Step 2: SMT Component Placement

With solder paste precisely applied, the board moves to pick-and-place machines—the workhorses of modern electronics assembly.

How Pick-and-Place Works

These machines are genuinely impressive pieces of engineering. A modern pick-and-place system:

1. Picks components from feeders (reels, trays, or tubes) using vacuum nozzles
2. Centers each component using optical alignment
3. Rotates the component to the correct orientation
4. Places it on the designated pad location with micron-level accuracy
5. Moves to the next component at speeds exceeding 100,000 placements per hour

The placement program is generated from your design files—specifically the centroid file (also called XY data or pick-and-place file) that specifies each component’s location, rotation, and reference designator.

Component Feeding Methods

Feed Type	Best For	Typical Components
Tape and Reel	High-volume, small components	Resistors, capacitors, small ICs
Tray	Larger or moisture-sensitive parts	BGAs, QFPs, connectors
Tube	Medium quantities, IC packages	DIP packages, some connectors
Loose/Bowl	Special handling requirements	Odd-form components

Placement Accuracy

Modern equipment achieves placement accuracy of ±25-50 microns—essential when working with fine-pitch components like 0.4mm pitch BGAs or 0201 passives. The tacky solder paste temporarily holds components in position until reflow soldering creates permanent connections.

Step 3: Reflow Soldering

Reflow soldering is where SMT assembly transforms from a collection of loosely held components into a permanently bonded assembly. Getting this step right is crucial—a poor reflow profile can damage components, create unreliable joints, or leave you with a board full of defects.

Understanding the Reflow Oven

Modern reflow ovens use convection heating with multiple independently controlled zones. As boards travel through on a conveyor, they experience a precisely choreographed temperature journey. High-end production ovens have 8-12 temperature zones, allowing fine control over the profile.

The oven’s atmosphere also matters. Nitrogen purging displaces oxygen, reducing oxidation of solder and component leads. While adding cost, nitrogen atmosphere improves wetting and reduces defects like head-in-pillow on BGA components.

The Reflow Profile

The board passes through a convection oven following a carefully controlled temperature profile with four distinct zones:

Preheat Zone (25°C to 150°C)

• Ramp rate: 1-3°C per second
• Purpose: Gradually raise board temperature, avoiding thermal shock to components
• Duration: 60-90 seconds

Thermal Soak Zone (150°C to 200°C)

• Purpose: Activate flux, remove volatiles, equalize temperature across the board
• Duration: 60-120 seconds
• Critical for reducing the temperature differential (Delta T) between small and large components

Reflow Zone (Peak: 235-250°C for lead-free)

• Time above liquidus (TAL): 30-60 seconds
• Purpose: Solder melts and wets component leads and pads
• Peak temperature typically 20-40°C above solder liquidus point

Cooling Zone

• Ramp rate: 2-4°C per second
• Purpose: Solidify solder joints with proper grain structure
• Controlled cooling prevents thermal shock and ensures joint reliability

Reflow Zone	Temperature Range	Duration	Purpose
Preheat	25°C → 150°C	60-90 sec	Gradual heating
Soak	150°C → 200°C	60-120 sec	Flux activation, thermal equalization
Reflow	Peak 235-250°C	30-60 sec TAL	Solder melting and wetting
Cooling	250°C → 25°C	Controlled descent	Joint solidification

Nitrogen Atmosphere

Many production lines use nitrogen during reflow to minimize oxidation. While this adds cost, it improves solder wetting and reduces defects like head-in-pillow on BGA packages.

Step 4: Automated Optical Inspection (AOI)

After reflow, the assembly undergoes its first major quality gate: Automated Optical Inspection.

What AOI Detects

Using high-resolution cameras and sophisticated image processing, AOI systems inspect for:

• Missing components: Empty pads where components should be
• Component presence: Verifying correct part at each location
• Orientation errors: Reversed polarity or rotated parts
• Solder defects: Bridges, insufficient solder, tombstoning
• Lifted leads: Component leads not properly seated
• Wrong component values: Detecting incorrect parts (within visible marking limitations)

AOI Capabilities and Limitations

AOI excels at surface-level defects but cannot see hidden connections. This is particularly important for:

• BGA solder balls (hidden under the package)
• QFN ground pads (also hidden)
• Internal PCB defects

For these, X-ray inspection is required.

Step 5: Through-Hole Component Assembly

Many boards combine SMT with through-hole components. After SMT assembly and inspection, through-hole parts are inserted—either manually or by automated insertion equipment.

Through-Hole Insertion Methods

Manual Insertion Used for low volumes, prototypes, or components that don’t suit automation. Operators insert components according to assembly drawings, typically using:

• Component sequence guides
• Anti-static workstations
• Insertion tools for tight spaces

Automated Insertion High-volume production uses automated insertion equipment for components like:

• Axial components (resistors, diodes)
• Radial components (electrolytic capacitors)
• DIP packages

Wave Soldering

For through-hole components, wave soldering is the traditional mass-soldering method:

1. Flux application: Spray or foam flux coats the bottom of the board
2. Preheating: Board temperature rises to 100-150°C to activate flux and reduce thermal shock
3. Wave contact: The board passes over a standing wave of molten solder (250-260°C for lead-free)
4. Cooling: Controlled cool-down solidifies joints

Wave soldering works well for pure through-hole boards but struggles with double-sided SMT assemblies where bottom-side components would be submerged in solder.

Selective Soldering

For mixed assemblies with SMT on both sides, selective soldering targets only the through-hole connections:

• A programmable solder nozzle applies solder to specific locations
• Bottom-side SMT components remain protected
• Individual parameter control for each joint

Soldering Method	Best For	Throughput	Precision
Wave Soldering	High-volume THT, single-sided boards	Highest	Moderate
Selective Soldering	Mixed technology, double-sided boards	Moderate	High
Manual Soldering	Low volume, rework, specialized joints	Lowest	Operator-dependent

Step 6: X-Ray Inspection (AXI)

When you cannot see a solder joint, you need to look through it. X-ray inspection (Automated X-ray Inspection, or AXI) is essential for:

• BGA packages: Verifying ball grid array connections
• QFN/QFP packages: Checking hidden ground pads
• PTH hole fill: Confirming adequate solder in plated through-holes
• Voiding analysis: Measuring void percentages in solder joints

What X-Ray Reveals

X-ray imaging shows:

• Solder voids (gas pockets that weaken joints)
• Head-in-pillow defects (incomplete BGA ball fusion)
• Bridging under components
• Cold joints and insufficient wetting

Modern 3D X-ray (computed tomography) can slice through the board layer by layer, inspecting multilayer assemblies without destructive testing.

Step 7: In-Circuit Testing (ICT)

ICT provides electrical verification that each component is present, correctly oriented, and within specification.

How ICT Works

The assembled board is placed on a bed-of-nails fixture—a custom test jig with spring-loaded probes that contact designated test points on the PCB.

ICT verifies:

• Component presence: Open circuit detection for missing parts
• Correct values: Resistance, capacitance, inductance measurements
• Shorts detection: Finding unintended connections
• Diode/transistor polarity: Verifying correct orientation
• IC pin connectivity: Confirming proper IC seating

ICT vs Flying Probe

Test Method	Setup Cost	Test Speed	Best For
Bed-of-Nails ICT	High (custom fixture)	Very fast	High-volume production
Flying Probe	Low (programming only)	Slower	Prototypes, low-medium volume

Flying probe testers use movable probes instead of a fixed fixture, trading speed for flexibility—ideal for prototype runs where custom fixtures aren’t economical.

Step 8: Functional Testing

While ICT verifies components, functional testing confirms the assembled board actually works as designed.

Functional Test Scope

Depending on the product, functional testing may include:

• Power-on testing: Verifying power supply rails, current consumption
• Signal integrity: Checking waveforms, timing, signal levels
• Communication verification: Testing serial buses (I2C, SPI, UART), wireless links
• Sensor calibration: Programming initial calibration values
• Firmware loading: Installing initial software
• Full system simulation: Testing the board in its intended operating environment

Test Coverage Strategy

A well-designed test strategy combines multiple methods:

1. AOI catches visual defects immediately post-reflow
2. X-ray inspects hidden connections
3. ICT verifies electrical connectivity and component values
4. Functional test confirms the design works as intended

Each layer catches different defect types; together they provide comprehensive quality assurance.

Step 9: Cleaning and Conformal Coating

Depending on your product’s requirements, post-assembly processing may include cleaning and protective coating.

PCB Cleaning

Flux residues left after soldering can cause long-term reliability issues if not addressed:

• No-clean flux: Designed to leave benign residues—often acceptable without cleaning
• Water-soluble flux: Requires deionized water washing
• Rosin flux: May require solvent or aqueous cleaning

Cleaning methods:

• Batch spray washers
• Inline conveyorized washers
• Ultrasonic cleaning for tight spaces

Conformal Coating

For products exposed to harsh environments, conformal coating provides a protective barrier:

Coating Type	Protection Level	Typical Applications
Acrylic	Moderate	Consumer electronics
Silicone	Good thermal range	Automotive, LED
Polyurethane	Excellent chemical resistance	Industrial, military
Epoxy	Maximum protection	Aerospace, harsh environments

Application methods include selective spray, dip coating, and brush application.

Step 10: Final Quality Control and Packaging

The final station in the PCB assembly process involves comprehensive quality verification and preparation for shipping.

Final QC Inspection

• Visual inspection for workmanship issues
• Verification of correct part markings and labels
• Dimensional checks if required
• Documentation verification (test records, certificates of conformance)

ESD-Safe Packaging

Electronic assemblies are sensitive to electrostatic discharge throughout their lifecycle:

• Anti-static bags (pink poly or metalized shielding bags)
• Moisture barrier bags with desiccant for moisture-sensitive assemblies
• Proper labeling including date codes and lot traceability
• Appropriate cushioning for shipping

PCB Assembly Process Flow Chart Summary

Here’s the complete PCB assembly process at a glance:

Step	Process	Key Purpose
0	DFM/DFA Check	Prevent manufacturing issues
1	Solder Paste Application	Deposit solder on SMT pads
2	SMT Placement	Position surface-mount components
3	Reflow Soldering	Permanently bond SMT components
4	AOI Inspection	Detect surface-level defects
5	Through-Hole Assembly	Insert and solder THT components
6	X-Ray Inspection	Inspect hidden connections
7	In-Circuit Testing	Verify electrical connectivity
8	Functional Testing	Confirm operational performance
9	Cleaning/Coating	Remove residues, apply protection
10	Final QC & Packaging	Quality verification, shipping prep

SMT vs Through-Hole: Choosing the Right Assembly Technology

One question I get asked frequently is when to use SMT versus through-hole components. The answer isn’t always straightforward, and understanding the tradeoffs helps you make better design decisions.

When to Choose SMT

Surface mount technology dominates modern electronics for good reasons:

Size and density: SMT components are dramatically smaller. A 0402 resistor measures just 1.0mm x 0.5mm—you could fit dozens where a single through-hole resistor would go. This enables the compact devices we use every day.

Speed: Pick-and-place machines can place SMT components at rates exceeding 100,000 components per hour. The automated reflow process then solders them all simultaneously. Through-hole assembly is inherently slower.

Cost: At volume, SMT assembly costs less per component due to automation efficiency and smaller board sizes.

Double-sided assembly: SMT components can be placed on both sides of the board, effectively doubling available real estate.

When Through-Hole Still Makes Sense

Despite SMT’s advantages, through-hole technology remains essential for specific applications:

High mechanical stress: Connectors that get plugged and unplugged repeatedly benefit from the mechanical anchor that through-hole leads provide. The solder joint extends through the board, creating a much stronger physical connection.

High power components: Power resistors, large capacitors, and transformers often use through-hole mounting for better thermal dissipation and mechanical stability.

Manual assembly considerations: If your product will be hand-assembled or repaired in the field, through-hole components are easier to work with using basic soldering equipment.

Legacy compatibility: Some specialized components simply aren’t available in surface-mount packages.

The Reality: Mixed Technology

Most production boards use both technologies. A typical design might have:

• 90%+ SMT components (resistors, capacitors, ICs)
• Through-hole for connectors, mounting hardware, and high-power components

This mixed approach lets you optimize each component choice while keeping the overall assembly process efficient.

Tips for a Successful PCB Assembly Process

Based on years of working with assembly houses and troubleshooting production issues, here are practical tips that can save you headaches:

Design Phase Tips

Work with your assembler early: Don’t wait until your design is complete to engage your assembly partner. Their DFM feedback during design saves redesign cycles.

Use standard footprints: Custom footprints are a common source of assembly problems. Use manufacturer-recommended land patterns or IPC-7351 standards.

Consolidate component values: Every unique part number adds procurement and inventory complexity. Standardizing on common values (10K resistors, 100nF capacitors) reduces BOM cost and supply chain risk.

Include test points: Design for testability from the start. Adding test access after layout is much harder than including it initially.

Mind your thermal relief: Components on large copper pours need thermal relief patterns, or they’ll act as heat sinks during soldering, causing cold joints.

Documentation Tips

Complete BOM information: Include manufacturer part numbers, not just values and packages. “10K 0603 resistor” leaves room for interpretation; a specific MPN doesn’t.

Clear assembly drawings: Mark component reference designators clearly. Indicate polarity for every polarized component. Include any special instructions.

Version control everything: Use revision numbers and dates on all documentation. Nothing causes more assembly confusion than mismatched file versions.

Communication Tips

Ask questions proactively: If something seems unclear, ask. Assembly technicians can’t read your mind, and assumptions lead to expensive mistakes.

Review the first article: Before production runs, request and carefully inspect a first article sample. This catches issues before they’re multiplied across hundreds of boards.

Establish change control: Any design change—even minor ones—should be formally communicated to your assembler with updated documentation.

Understanding PCB Assembly Costs

Cost is always a consideration, and understanding what drives assembly pricing helps you optimize your design and purchasing decisions.

Cost Factors in PCB Assembly

Component count: More components = more placement operations = higher cost. But don’t sacrifice functionality to reduce count—optimize by consolidating where possible.

Component types: Standard SMT parts are cheapest to place. BGAs, fine-pitch QFPs, and 0201/01005 packages require more precision and cost more. Through-hole components add manual handling or wave soldering steps.

Board complexity: Double-sided assembly costs more than single-sided. High layer counts, tight tolerances, and special finishes add cost.

Quantity: Setup costs (programming, stencils, fixtures) get amortized over volume. A 10-piece prototype run has much higher per-unit cost than a 10,000-piece production run.

Turnaround time: Quick-turn services command premium pricing. Standard lead times are more economical.

Turnkey vs Consigned Assembly

Turnkey assembly: The assembly house procures all components and bare boards. You provide documentation; they handle everything else. More convenient but typically higher cost.

Consigned assembly: You provide all components and bare boards; they perform assembly only. Lower cost but requires you to manage procurement and inventory.

Partial turnkey: You provide specialty or long-lead components; they source common parts. A middle ground that can optimize both cost and convenience.

Assembly Model	Your Responsibility	Cost	Best For
Full Turnkey	Documentation only	Highest	Convenience, low volume
Partial Turnkey	Long-lead/specialty parts	Medium	Cost optimization
Consigned	All components, boards	Lowest	High volume, controlled supply chain

Common PCB Assembly Defects and Solutions

Understanding common defects helps you design boards that avoid them:

Defect	Cause	Prevention
Solder bridging	Excessive paste, tight pitch	Proper stencil design, adequate pad spacing
Tombstoning	Uneven heating, pad imbalance	Thermal balance in layout, component orientation
Cold solder joint	Insufficient heat, contamination	Proper reflow profile, clean boards
Voiding	Trapped flux gases, moisture	Profile optimization, proper storage
Head-in-pillow	BGA warpage, oxidation	Nitrogen reflow, pre-bake components
Missing components	Placement error, lost parts	Proper programming, vacuum verification

IPC Standards for PCB Assembly

The electronics industry relies on IPC standards for consistent quality. Key standards you s

hould know:

Standard	Scope
IPC-A-610	Acceptability of Electronic Assemblies
IPC J-STD-001	Requirements for Soldered Electrical and Electronic Assemblies
IPC-7711/7721	Rework, Modification, and Repair of Electronic Assemblies
IPC-A-600	Acceptability of Printed Boards
IPC-2221	Generic Standard on Printed Board Design

IPC Classes Explained

IPC defines three product classes based on reliability requirements:

• Class 1: General Electronics—consumer products where cosmetic imperfections are acceptable if function is maintained
• Class 2: Dedicated Service Electronics—communication equipment, industrial controls where extended life is expected
• Class 3: High Reliability Electronics—aerospace, medical, military where failure is unacceptable

PCB Assembly for Different Industries

The PCB assembly process adapts to different industry requirements. Understanding these variations helps you select the right assembly partner and specify appropriate requirements.

Consumer Electronics

Consumer products prioritize cost and aesthetics:

• High-volume SMT assembly
• IPC Class 2 typically sufficient
• Cost optimization is paramount
• Rapid product cycles demand flexible manufacturing

Medical Devices

Medical applications require stringent quality controls:

• IPC Class 3 often required
• Full traceability of components and processes
• Clean room assembly for implantables
• ISO 13485 certified facilities
• Extended testing and documentation requirements

Automotive Electronics

Automotive PCBAs face extreme environmental demands:

• Extended temperature ranges (-40°C to +125°C)
• Vibration and shock resistance
• IATF 16949 certification required
• Long product lifecycles requiring 10+ years of component availability
• Conformal coating standard practice

Aerospace and Defense

The highest reliability requirements apply here:

• IPC Class 3 minimum, often with additional requirements
• AS9100 certification
• ITAR compliance for defense applications
• Extensive qualification testing
• Premium components with full traceability

Industrial and IoT

Industrial applications balance reliability with cost:

• IPC Class 2 or 3 depending on criticality
• Environmental protection (conformal coating, potting)
• Robust connectors and mounting
• Long operational lifecycles

Useful Resources and Tools

Free DFM Analysis Tools

• JLCDFM: Web-based DFM analysis for Gerber files (jlcdfm.com)
• NextPCB HQDFM: Downloadable DFM checking tool
• Most PCB manufacturers: Offer free DFM review with orders

Component and Reference Databases

Resource	Description	Link
Octopart	Component search and comparison	octopart.com
DigiKey	Comprehensive parametric search	digikey.com
Mouser	Component datasheets and stock	mouser.com
FindChips	Multi-distributor search	findchips.com
IPC	Official standards body	ipc.org
JEDEC	Semiconductor standards	jedec.org

Design Resources

• Sierra Circuits Knowledge Base: Excellent DFM guidance
• Altium Resources: PCB design best practices
• IPC Designer Council: Training and certification resources

Frequently Asked Questions

What is the difference between PCB and PCBA?

A PCB (printed circuit board) is the bare board—the substrate with copper traces, vias, and pads but no components. Think of it as the foundation and roadways of a city. PCBA (printed circuit board assembly) is the same board after components have been mounted and soldered, making it a functional electronic assembly—the city with all its buildings, utilities, and inhabitants.

The PCB is a component that you purchase from a fabrication house. The PCBA is a finished or semi-finished product that results from the assembly process, ready for integration into your end product.

How long does PCB assembly typically take?

Timeline varies significantly based on complexity, quantity, and assembly house capacity:

• Prototype (quick-turn): 24 hours to 5 days for small quantities
• Standard production: 1-3 weeks for medium volumes
• High-volume with component procurement: 4-8 weeks when components need sourcing

Turnkey services (where the assembly house procures components) typically add 1-2 weeks for component sourcing, depending on availability. Component lead times have become increasingly variable, so always confirm availability before committing to schedules.

The fastest turnaround requires having components in stock, design files ready, and working with an assembly partner who offers expedited services.

What files are needed for PCB assembly?

Minimum requirements:

• Gerber files: PCB Manufacturing data for the bare board (copper layers, solder mask, silkscreen, drill files)
• BOM (Bill of Materials): Component list with part numbers, values, package types, and reference designators
• Centroid/XY file: Component placement coordinates and rotation angles
• Assembly drawing: Visual reference showing component placement, orientation, and any special notes

Additional helpful files:

• Schematic (PDF or native format) for reference
• Test documentation and test point locations
• Special assembly instructions for sensitive components
• CAD files in native format (Altium, KiCad, Eagle)

Many assembly houses accept ODB++ or IPC-2581 formats, which bundle all necessary data into a single intelligent package.

What is the difference between SMT and THT assembly?

SMT (Surface Mount Technology) places components directly on the board surface using solder paste deposited through a stencil. Components are held in place by paste tackiness until reflow soldering permanently bonds them. SMT allows smaller components, higher density, and automated assembly at very high speeds. Most modern electronics use predominantly SMT assembly.

THT (Through-Hole Technology) inserts component leads through holes drilled in the board. These leads are then soldered on the opposite side using wave soldering, selective soldering, or manual techniques. THT provides stronger mechanical connections, making it preferred for connectors, high-power components, and parts subject to mechanical stress.

Most modern assemblies use both technologies—SMT for the majority of components and THT for specific applications requiring mechanical robustness.

How do I choose between different assembly houses?

Key evaluation criteria:

Technical capabilities: Do they handle your board complexity? Consider layer count, component types (BGAs, fine-pitch, 0201s), tolerances, and special requirements.

Certifications: ISO 9001 is baseline. Industry-specific certifications matter: AS9100 for aerospace, ISO 13485 for medical, IATF 16949 for automotive.

Volume fit: Some houses specialize in prototypes and quick-turn, others in high-volume production. Mixing these often results in poor service or pricing.

Location: Domestic assembly offers easier communication and faster turnaround. Offshore assembly (often China) typically costs less but requires longer lead times and careful quality management.

DFM support: Quality partners provide meaningful DFM feedback that improves your design. This support is invaluable, especially for complex boards.

Test capabilities: Confirm they have AOI, X-ray (if you have BGAs), ICT, and functional test capabilities appropriate to your product.

References and track record: Ask for references from customers with similar products. A house that excels at consumer electronics may struggle with medical devices, and vice versa.