S100B Desktop Selective Soldering Machine from Southern Machinery: Fixture-Less THT Soldering for High-Mix EMS

When a PCB assembly operation runs dozens of board variants in small batches, THT (through-hole) soldering is usually the most stubborn bottleneck. Hand soldering is slow and operator-dependent, full-size Wave Soldering needs dedicated pallets and long changeover time, and a large selective soldering line is hard to justify at low utilization. The S100B Desktop Selective Soldering Machine from Southern Machinery addresses exactly this gap: a compact, fixture-less selective soldering station designed for ultra-fast changeover in high-mix, low-volume (HMLV) PCBA production.

Southern Machinery (Shenzhen, China, est. 2011) designs and builds SMT/THT PCB assembly automation equipment and has served more than 237 customers worldwide, from EMS and ODM factories to automotive, medical, industrial control and power electronics manufacturers. The S100B is part of a broader selective soldering portfolio that also includes the SO-300, SO-300B and SL-600 platforms, so buyers can scale from a desktop station to an in-line process.

What Is This Machine Used For?

The S100B is a desktop selective soldering machine used to solder THT components onto a PCB without exposing the whole board to a Wave Soldering process. Instead of passing the complete board over a full-width solder wave, a selective soldering machine applies flux only to the joints that need it, then moves a small solder nozzle (or mini-wave) along a programmed path to solder each joint individually. Because the board is held and positioned by a programmable motion platform rather than a dedicated carrier, the S100B changes over between different PCB models without tooling or fixture changes — the differentiator highlighted in Southern Machinery's official product deep-dive video, titled "HMLV PCBA Ultra-fast changing without fixture."

In plain terms: load a PCB, call up the saved program, and the machine solders the programmed joints with repeatable quality. When the next board variant arrives, the operator calls up another program and starts again. No pallet, no fixture, no mechanical changeover.

SO-300B offline single-head selective soldering machine

SO-300B offline single-head selective soldering machine — part of the Southern Machinery selective soldering family.

Why High-Mix, Low-Volume Lines Struggle With THT Soldering

Hand soldering quality varies by operator. Solder joint appearance, wetting, dwell time and rework rates change with skill, shift and fatigue. Rework on a dense board is expensive and risks pad damage.
Fixtures and pallets are a hidden cost. Full-board Wave Soldering of boards with THT components on both sides, or with tall/heat-sensitive parts, usually requires carriers, masks or pallets. Each board variant needs its own tooling, and every tooling change adds changeover time.
Large selective or wave lines are underutilized at low volume. A full-size in-line selective soldering system is justified when utilization is high. For prototype, rework, NPI (new product introduction) and small-batch production, a desktop station is often the right economic fit.
Slow changeover kills throughput in HMLV. If a line takes 30–60 minutes to change pallets, programs and parameters for every batch, effective capacity collapses as batch size shrinks.

Typical Application Scenarios

PCB rework and repair stations. Re-soldering connectors, relays and other THT parts on boards that failed AOI or electrical test, without re-running the whole line.
Prototype and NPI departments. Verifying THT soldering on new designs before committing to pallet-based Wave Soldering tooling — and without dedicating production capacity.
Small-batch production of THT boards. Short runs of power supplies, control boards, instrument PCBs and similar products where a full Wave Soldering line is not economical.
Boards that cannot be wave-soldered. Double-sided assemblies with SMD and THT components on the same side, connectors on the backside, or heat-sensitive and tall components where selective soldering protects the rest of the board.
Line-side soldering station. Placed next to an SMT line or an auto-insertion cell to solder odd-form and connector components that are not inserted or soldered by the main process.
High-mix EMS and ODM factories. Multiple board variants per day, frequent engineering changes, and jobs that would otherwise be quoted as manual soldering.

How It Fits Into a Complete PCB Assembly Line

The S100B works as an offline, line-side or engineering station rather than a fixed position in a high-speed conveyor flow. A typical integration pattern in an EMS factory:

SMT front end. Solder paste printing, Pick and Place placement and Reflow Oven complete the SMD side.
THT insertion. Radial, axial or odd-form auto-insertion machines place through-hole components (Southern Machinery's S3000/S3010A, S4000 and odd-form platforms, for example).
Selective soldering. The S100B solders the THT joints that were inserted — either the full board or only the joints that cannot go through Wave Soldering.
Post-solder processing. Inspection (AOI/AVI), cleaning, lead cutting or selective repair, followed by final assembly.

For a factory that already runs Wave Soldering for high-volume products, the S100B complements it: high runners go through the wave line, while NPI, rework and low-volume variants go through the desktop selective station. For a factory without any wave line, the S100B can be the primary THT soldering resource during ramp-up. Because programs, solder temperature, flux and motion paths are stored per PCB, repeat production is a matter of recalling a file — the same traceability logic Southern Machinery documents for its SL-600 mini selective soldering machine, whose PC software stores the full PCB menu (dimensions, flux type, solder type, nozzle type, temperatures, motion path and per-site wave/Z heights) in a single file.

Key Selection Parameters to Confirm Before Buying

Southern Machinery publishes full specifications per model, and the right configuration depends on your boards. Before requesting a quote, prepare these parameters:

Maximum board dimensions and soldering area. Confirm the largest PCB the machine must handle (for reference, the offline single-head SO-300B in the same family is documented with a 300 × 250 mm maximum soldering area, customizable).
Positioning accuracy and repeatability. Needed for fine-pitch THT joints and consistent nozzle alignment (the SO-300B is documented at ±0.1 mm positioning accuracy; confirm the S100B value for your joint geometry).
Component types and joint count. Connector pins, relays, transformers, electrolytic capacitors, terminal blocks — and how many joints per board.
Flux system requirements. Spray/jet fluxing, flux type and solid content, and whether the flux tank capacity matches your batch size.
Solder alloy and Nozzle configuration. Lead-free alloys (e.g., SAC305) vs. leaded, nozzle inner diameters, custom nozzle shapes for specific pads, and solder pot capacity.
Nitrogen (N2) requirement. N2-assisted soldering improves wetting and reduces dross; decide whether the station needs N2 inline heating.
Preheating. Whether bottom/top preheat is needed for thick or thermally demanding boards.
Changeover expectations. Number of board variants per day and target changeover time — the core value of a fixture-less design.
Environment and utilities. Desktop footprint, power supply, compressed air, exhaust/fume extraction, and ESD requirements.
Software and traceability. Program storage per PCB, live camera monitoring, parameter logging, and MES connectivity if required.

ROI, Quality and Throughput Considerations

Removing fixture cost. No pallets or carriers per board variant means tooling cost shifts from hardware to software (programming), which is reusable and editable.
Reducing hand-solder rework. A programmed motion path gives the same dwell time, wave height and Z height for every joint on every board, removing the operator-to-operator variation that drives rework in manual THT soldering.
Better utilization of existing capacity. A desktop station keeps prototype, rework and small-batch work off the full-size line, protecting uptime for high-volume products.
Faster NPI. New boards can be soldered as soon as the program is created, without waiting for pallet fabrication.
Scalable investment. Start with one desktop station; add SO-300/SO-300B/SL-600 capacity or an in-line configuration as volume grows — all within one supplier's ecosystem of SMT, THT, Wave Soldering, board handling and inspection equipment.

Southern Machinery Selective Soldering Portfolio

S100B Desktop Selective Soldering Machine — fixture-less, ultra-fast changeover for HMLV PCBA; the subject of this guide.
SO-300 High-Speed Offline Selective Soldering Machine — compact offline system for PCB rework, flexible THT production and line-side soldering stations.
SO-300B Offline Single-Head Selective Soldering Machine — documented with 300 × 250 mm maximum soldering area (customizable), ±0.1 mm positioning accuracy, PC recipe control, N2-assisted soldering, five standard nozzles with custom shapes available, and a 15 kg solder pot.
SL-600 Mini Selective Soldering Machine — same XYZ motion platform performs selective fluxing and selective soldering; PC control with per-PCB menu, bottom preheat, N2 inline heating and live camera monitoring.
MSO-300 Offline Selective Soldering Machine — additional offline configuration in the selective soldering family.

All platforms share Southern Machinery's focus on PC-based recipe control, traceability and process repeatability, supported by the company's after-sales ecosystem: spare parts, training, retrofit, machine upgrading and repair services.

FAQ

What is the S100B desktop selective soldering machine used for? It is a compact, fixture-less selective soldering station for THT components, designed for high-mix, low-volume PCBA — including rework, prototypes, small-batch production and boards that cannot be Wave Soldered.

How is selective soldering different from Wave Soldering? Wave Soldering passes the whole board over a full-width solder wave (usually with pallets/masks to protect selected areas). Selective soldering applies flux and solder only to programmed joints via a moving nozzle, so the rest of the PCB stays untouched.

Does the S100B need a fixture or pallet for each PCB? The S100B is promoted by Southern Machinery as fixture-less with ultra-fast changeover — different PCB models are handled by recalling stored programs rather than changing mechanical tooling. Confirm exact board-size limits with the supplier for your specific PCBs.

What are typical S100B applications in an EMS factory? PCB rework and repair, NPI/prototype soldering, small-batch THT production, line-side soldering of connectors and odd-form parts, and soldering of double-sided boards where full-board Wave Soldering is not possible.

Which components can be selectively soldered? Connectors, relays, transformers, terminal blocks, electrolytic capacitors and other THT components with defined joint positions. Nozzle shape, solder alloy and flux are configured to the joint geometry.

How do I get configuration advice for the S100B? Contact Southern Machinery (Jason Wu, jasonwu@smthelp.com, +86 13602562576) with your board dimensions, component list and batch sizes. Product catalogs are available at file.autoinsertion.com and machine photos at ph.smthelp.com.

Contact Southern Machinery

The S100B and the full selective soldering portfolio are designed and manufactured in Shenzhen by Southern Machinery, a supplier of complete SMT/THT PCB assembly automation — insertion machines, Wave Soldering, board handling, cleaning, depaneling and inspection — for EMS, ODM, automotive, medical, industrial and power electronics manufacturers worldwide.

Email: jasonwu@smthelp.com
Phone/WhatsApp: +86 13602562576
Website: https://www.smthelp.com
Product catalogs: https://file.autoinsertion.com
Machine photo albums: https://ph.smthelp.com
Product video: S100B Desktop Selective Soldering Machine — HMLV PCBA ultra-fast changing without fixture

Send your PCB drawings and production volumes for a configuration recommendation and a selective soldering process proposal tailored to your line.