Automatic THT Assembly Line Solution for High-Volume PCB Production

THT vs DIP in High-Volume PCB Production

The terms THT and DIP are often used together, but they are not technically identical.

THT describes the mounting technology.

DIP means Dual In-line Package, which is one particular component package.

A through-hole production line may process:

• Connectors
• Capacitors
• Relays
• Transformers
• Inductors
• Terminals
• Switches
• Power components
• that are not DIP packages.

Nevertheless, the terms automatic DIP line and DIP production line are commonly used in electronics manufacturing to describe broader THT assembly operations.

Why Automate THT Assembly?

High-volume production can involve thousands of repetitive component insertions.

Manual assembly may create challenges such as:

• High labor requirements
• Variable cycle times
• Operator fatigue
• Insertion mistakes
• Difficult line balancing
• Increasing WIP
• Capacity limitations

Automation can be considered where the product structure is stable enough to support it.

Potential objectives include:

• Increasing repeatable production capacity
• Reducing repetitive manual work
• Improving line balance
• Supporting continuous PCB flow
• Improving process consistency
• Supporting production-data collection

However, automation should solve a measurable production problem.

Start with the BOM, Not the Machine

Before selecting an automatic insertion machine, analyze the actual THT BOM.

For every component, collect:

• Component type
• Package
• Dimensions
• Lead structure
• Lead spacing
• Orientation
• Polarity
• Packaging method
• Quantity per PCB
• Required insertion method

Then divide the components into groups.

Group 1: Components Suitable for Automatic Insertion

Some standardized THT components may support automated insertion when their:

• Geometry is compatible
• Leads are suitable
• Packaging supports automatic feeding
• Orientation is controlled
• Production quantity justifies automation

These components should be prioritized when evaluating automatic insertion.

Group 2: Components Suitable for Semi-Automatic Processing

Some parts may benefit from:

• Automatic component presentation
• Guided workstations
• Fixtures
• PCB positioning
• Visual work instructions

without requiring a fully automatic insertion machine.

Group 3: Components Better Suited to Manual Insertion

Manual insertion may remain practical for:

• Large transformers
• Irregular connectors
• Heavy components
• Low-quantity parts
• Components with difficult packaging
• Frequently changing components

Trying to automate every component can increase tooling, feeding, programming, and changeover complexity.

Component Packaging Matters

Two components with similar electrical functions may require different automation strategies because of their packaging.

THT components can arrive in:

• Tape
• Tube
• Tray
• Reel
• Bulk packaging
• Custom packaging

Automatic feeding becomes much easier when the component packaging supports consistent orientation and presentation.

Therefore, automation planning should include the component supply format—not just the component drawing.

Component Preparation for High-Volume Production

Before insertion, some THT components require:

• Lead cutting
• Lead forming
• Bending
• Straightening
• Sorting

If these operations remain fully manual while insertion is automated, component preparation can become the bottleneck.

For high-volume production, manufacturers should evaluate whether repetitive preparation operations can be:

• Automated
• Semi-automated
• Integrated with feeding

The objective is continuous material supply to the insertion process.

Typical Automatic THT Production Flow

A higher-automation line may use:

Automatic PCB Loader → Automatic THT Insertion → Assisted/Manual Insertion → Pre-Solder Inspection → Automatic PCB Transfer → Wave Soldering → Cooling → Post-Solder Inspection → Testing → Automatic Unloader

Optional functions include:

• Barcode scanning
• Automatic width adjustment
• Buffers
• Recipe management
• Traceability
• Production-data collection

The exact configuration should follow the actual product.

Automatic PCB Loading

Automatic loaders can feed boards into the production line without continuous manual loading.

When selecting PCB handling equipment, consider:

• PCB dimensions
• Panel dimensions
• PCB thickness
• Board weight
• Magazine dimensions
• Conveyor height
• Conveyor direction

For heavy PCBAs, board support and transfer stability may require additional consideration.

Automatic THT Insertion

Automatic insertion equipment can reduce repetitive manual placement of compatible components.

When evaluating a machine, review:

• Supported component types
• Feeding method
• PCB dimensions
• Insertion accuracy
• Insertion force
• PCB support
• Changeover
• Programming
• Maintenance
• Spare parts

Actual component compatibility

Nominal machine speed should not be the only selection criterion.

Rated Speed vs Actual Output

An insertion machine may have a high nominal insertion rate.

However, actual output can be affected by:

• Component mix
• Feeder arrangement
• PCB transfer
• Component quantity
• Insertion sequence
• Changeover
• Machine utilization
• Replenishment
• Manual operations

Therefore:

Machine Rated Speed ≠ Finished Line Output

Use actual PCB and BOM data to estimate cycle time.

Manual Insertion Can Still Be Part of an Automatic Line

A high-volume automatic THT line can still contain manual workstations.

For example:

Automatic Insertion → Manual Large-Component Insertion → Soldering

This may be more economical than developing automation for a small number of irregular components.

The key is to balance manual operations with the required takt time.

How to Calculate Manual Insertion Stations

Suppose the remaining manual THT components require a total of:

120 seconds of operator work per PCB

The required line takt is:

30 seconds per PCB

A simplified calculation is:

120 ÷ 30 = 4 operator-equivalent stations

Therefore, approximately four balanced workstations may be required before considering efficiency allowances, replenishment, changeover, and product variation.

This is more useful than simply adding operators after production starts.

Pre-Solder Inspection

Before soldering, inspect for:

• Missing components
• Wrong components
• Incorrect orientation
• Polarity errors
• Bent leads
• Incorrect seating
• Insertion depth problems

High-volume production can generate large quantities of defects quickly if an upstream assembly error is not detected.

Therefore, pre-solder inspection can help prevent repeated downstream rework.

Wave Soldering for High-Volume THT Production

Wave soldering is often an efficient option when:

• The PCB contains many THT joints
• The underside supports wave contact
• Production volume is high
• Continuous conveyorized production is required

A typical process includes:

Fluxing → Preheating → Wave Soldering → Cooling

Machine selection should consider:

• PCB width
• Conveyor capacity
• Fluxing system
• Preheat configuration
• Solder pot
• Wave configuration
• Cooling
• Controls
• Exhaust

Nitrogen where required by the process

Selective Soldering for High-Volume Production

Selective soldering can also be automated.

It may be useful when:

• THT joints are localized
• Bottom-side SMT limits wave contact
• Specific areas require controlled soldering
• Product design does not suit conventional wave soldering

However, selective soldering cycle time depends heavily on:

• Number of joints
• Soldering path
• Nozzle size
• Joint grouping
• Preheating
• Movement
• Number of soldering modules

For high-volume production, cycle-time calculation is especially important.

Wave vs Selective Soldering for High-Volume THT

Neither technology should be selected based only on production volume.

PCB design remains the primary consideration.

Preheating for THT Soldering

Preheating is important for stable soldering.

Its role can include:

• Flux activation
• Gradual PCB heating
• Reducing thermal differences
• Supporting wetting

However, there is no universal preheat setting.

The process depends on:

• PCB construction
• Copper distribution
• Component thermal mass
• Flux
• Solder alloy
• Equipment

High-volume production requires a validated process that remains stable over continuous operation.

Cooling and PCB Handling

After soldering, the PCB should cool sufficiently before downstream processing.

Cooling may be integrated into:

• Wave soldering equipment
• Selective soldering equipment
• Separate cooling conveyors

PCB handling should also consider:

• Large components
• Board weight
• Board warpage
• Component stability

For high-volume production, transport reliability is critical because even a simple conveyor fault can stop the complete line.

Post-Solder Inspection

Common THT soldering defects include:

• Solder bridges
• Poor wetting
• Insufficient solder
• Incomplete hole fill
• Excessive solder
• Icicles
• Solder balls
• Potential causes may include:
• Flux coverage
• Preheat
• Solderability
• Solder temperature
• PCB design
• Lead condition
• Conveyor parameters
• Wave stability
• Selective soldering settings

Inspection can include manual visual inspection, AOI where applicable, and other methods according to the product.

Testing Must Be Part of the Automatic Line Strategy

One of the most common mistakes in high-volume line planning is focusing on assembly automation while underestimating testing.

Depending on the product, downstream testing can include:

• ICT
• Programming
• Functional testing
• Communication testing
• Product-specific electrical testing

Testing cycle time must be included when calculating finished production capacity.

Example of a High-Volume Line Bottleneck

Consider:

Even though the automatic insertion machine can process 140 boards per hour and wave soldering can process 160, the finished line is approximately limited by testing at 70 boards per hour.

Purchasing a faster insertion machine would not solve the actual capacity problem.

Parallel Testing for High-Volume Production

If one test fixture requires 50 seconds per board and the target takt is 20 seconds, one station cannot support the required flow.

Manufacturers may need:

• Multiple test stations
• Parallel fixtures
• Automated routing
• Test buffers

Testing capacity should be calculated during initial line design rather than added after mass production begins.

Line Balancing Is the Core of High-Volume Automation

A high-volume THT line should balance:

Preparation → Automatic Insertion → Manual Insertion → Inspection → Soldering → Inspection → Testing

Useful metrics include:

• Takt time
• Cycle time
• WIP
• First-pass yield
• Downtime
• Changeover
• Rework
• Equipment utilization

The objective is maximum good finished output, not maximum machine speed.

Using Buffers in an Automatic THT Line

Buffers can help decouple processes with small cycle-time differences.

They may be useful between:

• Insertion and soldering
• Soldering and inspection
• Inspection and testing

However, buffers should not be used to hide a major bottleneck.

If testing produces 50 boards/hour while assembly produces 120, increasing buffer capacity only delays the accumulation problem.