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Selective Soldering

Selective Soldering
Details:
On Shenzhen STHL Technology Co., Ltd.'s production lines, Selective Soldering has become a core process for post-soldering mixed SMT and THT boards. When both sides of a PCB are densely populated with SMT components and certain through-hole devices must be soldered after placement, traditional full-board wave soldering can no longer meet the dual challenges of space constraints and thermal shock.

STHL employs Selective Through-Hole Soldering technology, using programmable soldering paths, nitrogen protection, and high-precision nozzles to perform "targeted" soldering on specific joints — protecting surrounding sensitive components while ensuring solder joint consistency and full traceability.
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Description
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Why Choose Selective Soldering

Space Constraints
Through-hole pads with as little as 1 mm clearance from surrounding SMT components.
Thermal Protection
Heat-sensitive components such as optical sensors and plastic-encapsulated connectors must be shielded from overall heating.
Consistency & Efficiency
Manual soldering often suffers from poor consistency, low efficiency, and high rework rates.
High-Mix Production
Ideal for high-mix, small-batch, and high-density mixed-assembly boards.

 

Basic Process

 

  • Spray Flux: Applied only to the target solder joint area, reducing residue and cleaning costs.
  • Preheating: Infrared plus top-mounted hot air convection to activate flux and minimize thermal shock.
  • Soldering: Localized contact between the PCB and molten solder wave for point-by-point soldering; temperature, dwell time, and wave height can be set independently.
  • Nitrogen Shielding: High-purity nitrogen (99.999%) prevents oxidation, reduces dross, and maintains a stable solder wave.
Selective Soldering

 

Process Types

Mini wave soldering

A small solder wave nozzle precisely delivers molten solder to the target joint, ideal for PCBs with tight spaces and dense components.

Selective Wave Soldering

Creates a localized wave in a specific area to batch-solder adjacent joints, balancing efficiency and precision.

Selective Soldering assembly

Fully automated production combining programmable routing, nitrogen shielding, and in-line inspection to achieve high-quality, consistent mass soldering.

 

Key Equipment and Process Elements

 

  • Nozzles: Diameters as small as 1.5 mm for confined areas; interchangeable sizes to match different joint requirements.
  • Solder & Solder Pots: Common lead-free alloys such as SAC305, operating at 270–300 °C; multiple pots can be configured for different alloys and nozzle types simultaneously.
  • Nitrogen Supply: High-pressure cylinders, liquid nitrogen tanks, or on-site nitrogen generators - the latter recommended for long-term cost efficiency.
  • Preheating System: Infrared heating combined with overhead hot air, with closed-loop temperature control for stability.
  • PCB Transport & Fixtures: Inline conveyors with load/unload stations; dual-track or dual-station designs to boost throughput.
PCB Transport

 

Applications

 

  • Post-soldering of high-density mixed-assembly boards.
  • Through-hole soldering near heat-sensitive components.
  • Partial soldering of multi-layer thick copper boards.
  • PCB Selective Soldering in high-reliability sectors such as automotive electronics, medical devices, and industrial control.

 

Advantages

 

  • Precision soldering that avoids thermal damage.
  • High consistency, reducing rework.
  • Automation lowers labor costs.
  • Traceable process data to meet quality audit requirements.

 

STHL's Differentiated Capabilities

 

STHL operates multiple imported Selective Soldering systems, supporting dual-mode switching between mini wave soldering and Selective Wave Soldering, with soldering accuracy up to ±0.05 mm. Backed by 20 years of PCBA manufacturing expertise, a full-process MES execution system, and 100% AOI/X-ray inspection, we maintain exceptional consistency in solder joint appearance and electrical performance during mass production.
Whether meeting automotive-grade standards or the precision demands of medical devices, STHL delivers high-precision, low-thermal-shock, and fully traceable Selective Soldering assembly solutions.

Selective Soldering-2

 

Summary & Collaboration Invitation

 

In through-hole soldering, Selective Soldering has become the preferred process for high-mix production and high-reliability applications. If your PCB design involves space limitations, heat-sensitive component protection, or extremely high consistency requirements, STHL's Selective Soldering solutions can provide complete support - from process evaluation and path programming to volume production.

 

Send your Gerber files and requirements to: info@pcba-china.com - Let us deliver a high-standard Selective Soldering process that safeguards your product's performance and delivery schedule.

 

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