SL-600 Mini Selective Soldering Machine by Southern Machinery: Selective Fluxing and Soldering in One Compact Platform

Hand-soldering THT joints is one of the last manual steps left on many SMT assembly lines — and it is usually the step that limits throughput, drives operator-to-operator variation, and makes traceability hard. Selective soldering moves that work onto a programmed machine: flux is applied only where it is needed, the board is preheated from above and below, and a small solder wave contacts one joint set at a time.

The SL-600 is Southern Machinery's compact mini selective soldering machine. It is built for factories that need selective soldering quality without the footprint — and the cost — of a full in-line selective soldering cell. This article explains what the SL-600 is used for, how it is configured, what the published specifications actually say, and what a buyer should confirm before ordering.

Southern Machinery is a Shenzhen-based designer and manufacturer of SMT and THT PCB assembly automation equipment, founded in 2011 and serving more than 237 customers worldwide. Alongside selective and Wave Soldering equipment, the company supplies auto insertion, board handling, stencil printing, inspection and cleaning machines, so the SL-600 can be quoted as a single machine or as part of a complete PCB assembly line.

Southern Machinery selective soldering machine in operation

What is the SL-600 mini selective soldering machine?

The SL-600 is a mini selective soldering machine that integrates selective fluxing and selective soldering on one motion platform. The PCB is held fixed in a clamping conveyor while the machine's XY (fluxing) and XYZ (soldering) motion tables move to each programmed solder site.

Southern Machinery describes the platform as an integrated, full-functional, compact design: one chassis carries the fluxing system, the preheat system, the solder pot and the conveyor, so the machine occupies a single station instead of a multi-module line.

Key architecture, as published in the SL-600 user manual:

PCB fixed, tooling moving — the board stays clamped while the flux and solder platforms travel to each programmed site.
Separate fluxing and soldering motion tables — the fluxing table works in X and Y; the soldering table works in X, Y and Z.
Servo-driven, ball-screw and linear-rail guidance — with Panasonic servo motors on the soldering axis.
Dust-proof plate above the motion table — to keep flux and solder splash away from the ball screw.

What is this machine used for?

The SL-600 is used to solder through-hole joints selectively on PCBs that also carry SMD components — the classic use case being a mixed-technology board that passes through Reflow Oven processing first and then needs its THT connectors, terminals, transformers, relays and shielding soldered afterwards.

Typical questions buyers ask about this class of machine, answered directly:

Q: What is selective soldering used for? It solders only the through-hole joints that need it, without exposing the whole assembly to a wave. That protects nearby SMD parts, keeps heat local, and produces repeatable joints from a stored program rather than from operator skill.

Q: Can the SL-600 replace hand soldering on a THT line? For repetitive boards with a defined set of solder sites, yes — that is the point of the platform. Its value comes from repeatability: the same path, wave height, dwell time and temperatures are replayed for every board.

Q: Does it need a carrier? Southern Machinery's published specification states a PCB carrier is necessary, with a maximum carrier size of L600 × W600 mm. Board-to-carrier tooling is a normal part of a selective soldering project and should be quoted with the machine.

Q: Is it an in-line machine or a standalone machine? The standard configuration is an offline, manually loaded machine. Southern Machinery publishes a modular SMEMA online transportation design as an option so customers can form a flexible in-line configuration.

How selective soldering works on the SL-600

1. Selective fluxing

The fluxing table carries an imported flux jetting valve that deposits a small, precise flux dot at each solder site. Southern Machinery notes that the flux solid content should be kept below 8% for correct jetting performance. Flux is held in a 1 litre tank and fed through a pneumatic pressure tank, and the published design keeps flux pressure stable regardless of how much flux remains in the tank.

2. Preheat

Preheat is upper and bottom infrared (IR) heating, with the heater rated at 6 kW and a published temperature range of 25–240 °C. The heating ratio is adjustable from 0–100% through the PC software, and the preheat position is adjustable. Upper and bottom preheat matters on mixed-technology boards because the thermal mass of a thick PCB or a heavy connector often needs help from both sides before the solder wave arrives.

3. Selective soldering with N2

The solder pot has a 15 kg capacity, is made of titanium rather than a material that can leak, and uses an external cast-iron heater for fast heat-up. It is connected with a quick connector so the pot can be swapped without re-wiring. Five soldering Nozzles are supplied as standard — ID 4 mm × 3 pieces, 5 mm and 6 mm — and the conveyor design is stated to allow the solder Nozzle to approach to within 3 mm of the board edge.

An inline N2 heating system is part of the standard soldering arrangement. Nitrogen is used to improve wetting and reduce solder dross. The published facility requirement is 3–4 bar N2 pressure, a flow greater than 2 cubic feet per hour, and purity better than 99.998%. The pot also includes solder level checking with alarm and an over-temperature alarm.

4. Software, recipes and traceability

The SL-600 runs on a PC and monitor with Windows 10-based software, with a live camera on the monitor. Paths are programmed over a scanned picture of the PCB, and moving speed, dwell time, empty-move speed, Z height and wave height can be set for each individual solder site.

Every board program is stored as a single file that records PCB dimensions and picture, flux type, solder type, solder Nozzle type, solder temperature, N2 temperature, motion path, and each site's wave height and Z height. Critical parameters such as temperature, speed and pressure are monitored by the PC software. In practice this means a repeat build can be retrieved and replayed exactly, which is what makes the process auditable.

An optional upgrade adds automatic wave height calibration, checking and correcting wave height after a set number of PCBs to hold stability across a production run.

Typical application scenarios

Selective soldering earns its place wherever through-hole joints still exist on an otherwise surface-mount board:

High-mix, low-volume EMS production — many customers, frequent changeovers, and programs stored per PCB rather than re-taught by hand.
Power supply and LED driver boards — transformers, large electrolytics, terminals and heatsink-mounted parts that cannot go through a wave.
Appliance control boards — air conditioner, microwave, rice cooker, induction cooker and similar control PCBs with mixed SMT and THT content.
LED lighting and display assemblies — where heat-sensitive LEDs and long boards make a full wave impractical.
Automotive, medical and industrial control boards — applications where repeatability and traceability of the soldering process carry more weight than raw speed.
Prototype, NPI and rework cells — where the same machine that validates a process also supports after-sales repair of field returns.

How the SL-600 connects to a complete PCB assembly line

The SL-600 is normally placed at the through-hole stage of the line, after SMT placement and reflow and before final inspection, cleaning and coating. A typical Southern Machinery line sequence for a mixed-technology product runs:

Bare board loading and handling — destacker, magazine loader, vacuum loader, buffer conveyors and PCB flippers (SLC460, S-MLD350, S-V500, S-350C, S-AT500).
Stencil printing and paste inspection — stencil printer plus SPI (SP-1008 class, SH8650 3D SPI).
SMT placement — Pick and Place machines such as the S-800S eight-head mounter.
Reflow — lead-free Reflow Oven (STE-800 dual-lane, 8-zone).
THT component insertion — axial (S4000), radial (S3000 / S-3010B) and odd-form (S7020 / S7040 / S7900) auto insertion machines.
Through-hole soldering — Wave Soldering (S-WS450, S-WS350B) for wave-suitable boards, or selective soldering (SL-600) where only specific joints may be soldered.
Lead trimming, cleaning and inspection — inline auto lead cutter (S-320AT), PCBA cleaning (SME6200 / SCM5600D), AOI, and NG/OK unloading (SBH series).
Coating and finishing — selective conformal coating (SC9200 / STZ-P350) and packaging.

Because the SL-600 can be configured with SMEMA modular online transportation, it can be presented to an existing conveyor interface rather than being isolated on a bench. If the process is offline, the same machine still receives boards in carriers from the insertion area. Either way, Southern Machinery supplies the upstream and downstream equipment, which avoids the common problem of a new soldering cell that will not mechanically or electrically interface with the rest of the line.

Published SL-600 specifications

The following values are taken from the SL-600 selective soldering machine user manual published by Southern Machinery.

Item	Published specification
Model	SL-600 (mini selective soldering)
Overall dimensions	L1500 × W2200 × H1700 mm (includes release mechanism)
General power	12 kW
Consumption power	4–6 kW
Power supply	Single phase 220V, 50 Hz
Net weight	900 kg
Control	PLC + controller, with PC and monitor (Windows 10-based software)
Conveyor width	100–600 mm
Conveyor board thickness	1–4 mm
Conveyor type	Manual (standard); modular SMEMA online transportation available
Conveyor clearance	160 mm top, 30 mm bottom
Conveyor load	Less than 30 kg
Conveyor height	900 ± 30 mm
Max carrier size	L600 × W600 mm
PCB edge to Nozzle	3 mm
Fluxing motion table	X, Y axes, servo control, position accuracy ±0.05 mm
Soldering motion table	X, Y, Z axes, servo control, Panasonic servo motor, ball screw
Flux system	Imported jet valve, stainless steel Nozzle, 1 L flux tank, pneumatic pressure tank
Flux solid content	Should be below 8%
Preheat	Upper and bottom IR, 6 kW heater, 25–240 °C, 0–100% ratio adjustable by PC
Solder pot	15 kg capacity, titanium, external cast-iron heater, quick connector, impeller and tunnel
Standard soldering Nozzles	ID 4 mm × 3 pcs, 5 mm, 6 mm
N2 system	Inline heating; 3–4 bar pressure; >2 cubic feet/hour; purity >99.998%
Air supply	3–5 bar; 8–12 L/min
Exhaust requirement	500–800 cbm/h

Source: SL-600 selective soldering machine user manual (PDF) — published by Southern Machinery.

Key selection parameters to confirm before you order

A selective soldering project is defined by the board, not by the machine alone. Before quoting an SL-600 configuration, confirm:

Solder site map and count — how many joints per board, how many boards per hour, and which side of the board they sit on.
Maximum and minimum board size, thickness and carrier plan — including the last-process carrier, since the published maximum carrier size is L600 × W600 mm and a carrier is required.
Required soldering area and conveyor width — the published conveyor width range is 100–600 mm; confirm it covers your largest and smallest boards.
Nozzle sizes for the joint types — the standard set is ID 4 mm × 3, 5 mm and 6 mm; unusual connector geometries may need a different or custom Nozzle.
Flux chemistry and solid content — the published guidance is below 8% solid content for the jet valve.
N2 availability and purity — 3–4 bar, purity better than 99.998% is published; a factory without an N2 supply must plan for a generator or bottled supply.
Exhaust and facility requirements — 500–800 cbm/h exhaust, 3–5 bar shop air at 8–12 L/min, single-phase 220V 50 Hz power.
Inline or offline decision — whether the machine should be a standalone cell or integrated through SMEMA online transportation.
Recipe, traceability and MES requirements — which parameters your quality system needs recorded, and whether the machine has to exchange data with production software.
Local voltage and plug configuration — confirm the supply arrangement for your site.
Spares, Nozzle stock and training — consumable Nozzles and pot maintenance should be planned as part of the operating budget.

ROI, quality and throughput

Selective soldering is usually justified on three fronts, and all three are auditable in the SL-600's published design:

Quality and repeatability. The machine replays a stored program for every board instead of relying on operator technique. The fluxing table's published position accuracy is ±0.05 mm, preheat is controlled from 0–100% by software, and solder temperature, N2 temperature, wave height and Z height are all parameters held per solder site. The optional automatic wave height calibration corrects the wave after a set number of boards, which is the practical answer to drift within a long production run.

Throughput and labour. Moving THT joints from a bench to a program releases operator time, removes the bottleneck that otherwise sits between reflow and final test, and reduces the rework loop. Southern Machinery positions the SL-600 as an integrated, compact machine with fast motion — a cast-aluminium motion table and servo drive — so the cycle time is set by the path program rather than by how fast someone can hold an iron.

Cost of ownership and uptime. N2 inline heating reduces solder dross. The solder pot is titanium and connected by quick connector, so pot exchange does not require re-wiring — a maintenance job that can otherwise cost a production shift. Solder level checking, over-temperature alarms and material-shortage style monitoring reduce the chance of a silent process error turning into a batch of scrap.

For a factory already paying for hand-soldered THT joints, the comparison that matters is cost per good joint: labour plus rework plus scrap on the manual side, against machine depreciation, N2, flux, solder and Nozzles on the automated side. Southern Machinery can model this against your actual board mix during configuration.

What the SL-600 documentation does not state

To keep this guide useful rather than promotional, here is what the published user manual does not specify, and which must therefore be confirmed directly with Southern Machinery for your build:

No CE, UL or other certification mark is stated in the manual text.
No cycle time, joints-per-hour or CPH figure is published for the SL-600 — throughput depends entirely on your board's solder site count and path program.
No soldering area (X–Y travel envelope) figure is published in the manual; the carrier limit is L600 × W600 mm.
No flux consumption per board is published.
No price, lead time or warranty terms are published here.
No MES protocol list is published for this machine; data integration must be discussed against your production software.

FAQ

What is the SL-600 used for? It is a mini selective soldering machine for through-hole joints on mixed-technology PCBs. It selectively fluxes, preheats and solders individual joints on a fixed board, replacing hand soldering on repetitive production and supporting rework.

How is selective soldering different from Wave Soldering? Wave Soldering passes the whole board over a solder wave, which suits boards where all through-hole joints may be soldered at once. Selective soldering contacts only the joints that are programmed, which suits boards with SMD parts, heat-sensitive components or connectors that must not see a full wave. Many factories run both on the same line.

Does the SL-600 require a carrier or fixture? Yes — Southern Machinery's published specification states a PCB carrier is necessary, with a maximum carrier size of L600 × W600 mm.

What Nozzles are supplied with the machine? Five soldering Nozzles come as standard: ID 4 mm × 3 pieces, plus 5 mm and 6 mm. Custom Nozzle geometries can be discussed for unusual connector layouts.

What facility services does the SL-600 need? Published requirements are single-phase 220V 50 Hz power (12 kW general, 4–6 kW consumption), shop air at 3–5 bar and 8–12 L/min, N2 at 3–4 bar with purity better than 99.998%, and exhaust of 500–800 cbm/h.

Can the SL-600 work in-line with other machines? Yes. The standard machine is manually loaded, and Southern Machinery publishes a modular SMEMA online transportation design as an option for flexible in-line configuration.

Next step: get a configuration recommendation for your board

Selective soldering is specified around a solder site map, a carrier plan and a facility check — not around a catalogue page. Send Southern Machinery your board size, solder joint list and target takt time, and the team will come back with an SL-600 configuration, Nozzle set and integration proposal.

Contact: Jason Wu, Co-Founder — jasonwu@smthelp.com | +86 13602562576
Browse the machine catalogue: file.autoinsertion.com
See machine photos and line references: ph.smthelp.com
Company website: smthelp.com

Southern Machinery also quotes the surrounding equipment — THT auto insertion, Wave Soldering, board handling, cleaning, inspection and coating — so the selective soldering cell can be delivered as part of a complete PCB assembly line.