S100B Desktop Selective Soldering Machine: Fixture-Less THT Soldering for High-Mix, Low-Volume PCB Assembly

For EMS and ODM factories running high-mix, low-volume (HMLV) boards, through-hole soldering is usually the bottleneck: a full Wave Soldering line needs dedicated fixtures, and hand soldering is slow and inconsistent. The S100B desktop selective soldering machine from Southern Machinery (Shenzhen, established 2011; serving 237+ global customers) targets exactly this gap — programmable selective fluxing and soldering with ultra-fast changeover and no fixture.

What is this machine used for?

The S100B is a desktop selective soldering machine used to solder THT (through-hole) components on PCB assemblies where a full Wave Soldering line is not practical. Instead of passing the whole board over a solder wave, the machine moves the PCB over a controlled solder nozzle and applies solder only to the programmed joints. That makes it a fit for:

• High-mix products where board types change frequently
• Boards with mixed SMT and THT areas that cannot tolerate full-board wave exposure
• Prototype and engineering sample runs
• PCB rework and repair soldering
• Offline, line-side soldering stations beside an SMT or THT line

Selective soldering is the middle route between hand soldering and full Wave Soldering: it automates the process, keeps solder away from heat-sensitive SMT components, and removes the fixture cost and setup time of a wave machine.

Why choose selective soldering over wave or hand soldering?

Decision factor	Hand soldering	Full Wave Soldering	Selective soldering (S100B class)
Fixture need	None	Dedicated pallets/fixtures per board	None in the HMLV fixture-less workflow
Changeover time	Instant, but slow per joint	Long setup per product change	Fast — change the program, not the tooling
Thermal exposure	Localized (iron tip)	Whole board over the wave	Only programmed joints see solder
Consistency	Operator dependent	High	High — PC-controlled paths
Labor per joint	High	Low	Low
Best fit	Low volume, low complexity	High volume, stable product mix	High-mix, low-volume, rework, mixed technology

For HMLV production, the deciding cost is usually changeover and fixture overhead, not raw joint speed — which is exactly what a fixture-less desktop selective soldering machine removes.

Typical application scenarios

• EMS and ODM factories running 10-100 board types per day with 5-50 THT joints per board
• Automotive electronics: connectors, relays, coils and terminal blocks on mixed-technology boards
• Medical device PCBA: low-volume, high-reliability assemblies where solder quality must be repeatable
• Industrial control: PLC and instrumentation boards with large through-hole parts
• Prototype and NPI departments: engineering samples and pre-production validation
• Rework and repair stations: controlled soldering of specific joints without reflowing the whole board
• LED lighting and power supply lines needing a compact soldering station beside the main line

How to integrate the S100B into a complete PCB assembly line

The S100B is an offline, desktop machine: boards are loaded and unloaded manually, and the soldering process runs automatically from a PC program. Typical integration points:

• After SMT placement and Reflow Oven — solder THT components on boards that were only partially assembled on the SMT line.
• After THT auto insertion — finish the through-hole joints after axial, radial or odd-form insertion.
• Beside the main line — as a flexible soldering station for small batches and rework without stopping the primary line.
• Before AOI — so finished boards enter inspection with complete, repeatable solder joints.

Southern Machinery supplies whole-line solutions beyond a single machine: SMT Pick and Place, THT auto insertion (axial, radial, odd-form), Wave Soldering, board handling conveyors, stencil printing, and inspection equipment such as SPI and AOI. The S100B can be quoted as part of a complete PCB assembly line or as a standalone station for an existing factory.

Key selection parameters to confirm

Before quoting, buyers should verify these parameters against their own boards (specify values per project — do not assume defaults):

• Maximum solder area — the largest PCB size the machine must handle
• PCB thickness range and edge clearance required by your board design
• Positioning accuracy of the X/Y/Z motion table
• Fluxing method (e.g., selective jet valve) and flux tank capacity
• Preheat type and power (e.g., bottom IR) and temperature range
• Solder pot capacity, maximum solder temperature, and melting time
• Nozzle set — standard sizes supplied and customization options for unusual joint shapes
• Nitrogen requirements — purity, pressure and flow per nozzle (for dross reduction and wetting)
• Utilities — power supply, compressed air, and exhaust requirements for your site
• Footprint, weight and operating height for your floor layout

Southern Machinery documents reference configurations on smthelp.com. The offline single-head SO-300 series, for example, lists a 300 × 300 mm max solder area, ±0.1 mm positioning accuracy, a 15 kg solder pot, and 3 kW bottom IR preheating (25–240 °C) in its reference specification. Ask the supplier for the S100B configuration sheet matched to your specific boards.

ROI, quality and throughput perspective

Labor. One operator loads and unloads boards instead of hand-soldering every joint. For boards with many THT joints, the labor saving per board is direct and easy to calculate.

Quality. Programmed motion paths, dwell time, Z height and wave height repeat joint-to-joint and board-to-board. Consistent wetting reduces cold joints, bridging and touch-up — and each saved rework loop saves material, time and potential board damage.

Changeover. No fixture means product change takes minutes (load a new program, maybe change a nozzle) instead of the hours a wave line needs for fixture change and process stabilization.

Throughput reality. Selective soldering is slower per board than full Wave Soldering — that is by design. The correct ROI comparison for HMLV factories is selective soldering versus hand soldering plus rework, not versus wave. When fixture cost, setup time and rework are included, the net cost per good board usually favors automated selective soldering.

MES and traceability. PC-based recipe saving gives repeatable, documented process settings — useful for automotive and medical quality systems and for MES data collection.

FAQ

What is a desktop selective soldering machine? A compact selective soldering system that automates THT joint soldering by moving the PCB over a controlled solder nozzle, applying solder only to programmed locations. "Desktop" refers to its small footprint compared with full-size Wave Soldering lines.

What can the S100B solder? Through-hole components such as connectors, relays, coils, terminal blocks, and other THT parts on boards where selective, program-controlled soldering is preferred — including mixed SMT/THT assemblies, high-mix products, prototypes and rework.

Do I need nitrogen? Many selective soldering processes benefit from nitrogen, which improves wetting and reduces solder dross. Confirm the purity, pressure and flow requirements for your solder alloy and quality targets with the supplier.

How fast is changeover? The fixture-less HMLV workflow is designed for fast changeover — the program changes, not the tooling. Confirm exact changeover procedure and times with Southern Machinery for your product set.

Can it be integrated into an existing SMT line? Yes. The S100B is an offline station, so it can sit beside an existing line or in a rework area, and can be included in a complete Southern Machinery PCB assembly line (SMT, THT, Wave Soldering, board handling, SPI/AOI).

How do I get a configuration and quote? Contact Southern Machinery with your PCB dimensions, joint count, solder alloy and production volume. They will confirm solder area, nozzle set, nitrogen and utilities before quotation.

Contact Southern Machinery for a configuration recommendation

The right selective soldering configuration depends on your board design and product mix. Contact Southern Machinery (Jason Wu, Sales & Service Engineer) at jasonwu@smthelp.com or +86 13602562576 for a recommendation matched to your PCBs.

• Browse the full machine catalog at file.autoinsertion.com
• See machine photos at ph.smthelp.com
• Watch the S100B in action: https://www.youtube.com/watch?v=5R8P21iaOZg
• Learn more at www.smthelp.com

Southern Machinery — Shenzhen, established 2011 — SMT and THT PCB assembly automation equipment and whole-line solutions for EMS, ODM, automotive, medical and industrial electronics manufacturing.