Running RoHS and Non‑RoHS on the Same SMT Line: – Amarpreet Singh

amarpreet41
January 5, 2026

Running RoHS (lead‑free) and non‑RoHS (leaded) products on the same SMT line is possible, but only with strict process control and clear separation to avoid even tiny lead contamination of RoHS assemblies. Below is a step‑by‑step, practical plan for converting and managing a mixed‑mode line, plus key risks and how to mitigate them.

1. Basics: What Changes Between Non‑RoHS and RoHS

Non‑RoHS (leaded): Usually Sn63/Pb37 or Sn60/Pb40 solder; melting point around 183 °C; lower reflow and wave temperatures.
RoHS (lead‑free): Typically SAC (Sn‑Ag‑Cu) alloys; higher melting point (217–221 °C); needs higher reflow and wave temperatures and tighter process windows.
Critical point: Even small lead carry‑over into a RoHS product can push lead content above the 0.1% limit and fail compliance.

Because of this, best practice is to physically separate RoHS and non‑RoHS processes. When you must share the same line, you need disciplined changeover and clear rules.

2. Plan Before You Start

2.1 Policy and Flow Direction

Define a formal policy:
- Prefer running leaded first, then lead‑free, NEVER the other way around without full decontamination.
- If you must switch back from RoHS to leaded for commercial reasons, treat it as a full changeover, not a quick flip.
Fix routing rules:
- RoHS PCBs must never pass through equipment that currently has leaded solder still in it (e.g., wave pot, reflow oven with visible leaded paste).

2.2 Labelling and Traceability

Use clear, permanent labels on:
- Pastes, bars, wire, flux: “RoHS – Lead‑Free” (green) vs “Pb – Non‑RoHS” (red).
- Feeder carts, squeegees, spatulas, reflow profiles, racks.
Implement lot‑level traceability: each PCB lot tagged as RoHS or non‑RoHS for full audit trail.

3. Step‑by‑Step: Converting a Line from Non‑RoHS to RoHS

This covers full SMT line: paste print → placement → reflow → (optional) wave → hand solder.

3.1 Stencil Printer & Paste Area

Remove all leaded materials
- Take away leaded paste jars, squeegees, scrapers, cleaning rolls from printer and nearby benches.
Deep clean printer
- Clean stencil clamp area, underside wiper system, paste contact zones with approved solvent.
- Replace printer paper rolls, squeegee blades, it is must.
Use RoHS‑dedicated tooling
- Load RoHS‑only stencil if design differs; keep stencils coded for RoHS.
- Use green‑marked squeegees dedicated to lead‑free.
Introduce lead‑free paste
- Load machine with SAC paste; verify storage and expiry.

3.2 Pick‑and‑Place

Leaded vs RoHS risk here is lower (no molten solder yet), but residue from paste and handling still matters.

Clean contact surfaces
- Wipe conveyor rails, board supports, and vacuum nozzles where old paste may sit.
Feeder and reel controls
- Ensure components for RoHS build are RoHS‑compliant (material declarations from suppliers).
Program checks
- Separate programs for RoHS vs non‑RoHS with proper naming (e.g., “_LF” suffix).

3.3 Reflow Oven

The oven is one of the most sensitive points.

Bake‑out / purge
- Run empty boards with lead‑free paste through to help flush out residual leaded flux and solder from walls/rails.
- Clean infeed & outfeed, centre supports, and chains with approved high‑temp cleaner.
Profile change
- Build and lock a lead‑free profile: slower ramp, higher peak (~240–250 °C) and controlled cooling.
- Validate on representative RoHS PCBA with thermocouples.
Document “RoHS clean” status
- After cleaning and profile validation, mark oven with a status card (“RoHS mode – date/time”).
- Limit further leaded use unless you plan a full reverse clean.

3.4 Wave / Selective Solder (If Shared)

Sharing wave between leaded and RoHS is high‑risk because solder pot alloy is the main contamination source.

Best practice: separate pots or machines for RoHS and non‑RoHS.
If only one pot, you must:
1. Dump, clean, and recharge the pot with lead‑free alloy when moving from leaded to RoHS.
2. Clean nozzles, fingers, pallets, solder mask dams thoroughly.
3. Verify alloy composition via analysis to confirm lead content below RoHS thresholds.

In practice, the cost and downtime usually push plants to dedicate wave equipment.

3.5 Hand Soldering / Rework

Keep separate RoHS and non‑RoHS stations:
- Dedicated irons, tips, wire, flux, tip cleaner per category.
Colour‑code mats and tools; do not move irons between stations.
Train operators on health and compliance differences.

4. Running Both RoHS and Non‑RoHS on the Same Line (Daily Operation)

4.1 Scheduling Strategy

Wherever possible, run non‑RoHS (leaded) blocks first, then switch to RoHS and stay in RoHS for as long as possible.
Minimise the number of changeovers per week; convert only when a certain batch size or window is reached.

4.2 Changeover Checklist (Leaded → Lead‑Free)

Prepare a standard checklist covering:

Printer cleaned and stocked with RoHS paste and tools.
Pick‑and‑place feeders and programs switched to RoHS job.
Reflow oven in RoHS profile and marked “RoHS mode.”
Wave pot status: either RoHS‑dedicated or confirmed lead‑free alloy.
Hand soldering stations set with RoHS wire and tips.

Require sign‑off by line leader and QA before the first RoHS panel is released.

4.3 Documentation and Sampling

Keep RoHS process logs (date, time, lot, equipment status) for audits.
Periodically send solder joint samples or pot alloy samples for external lab analysis to confirm lead content below limits.

5. Converting Back: RoHS to Non‑RoHS

Moving from RoHS back to leaded is less critical from a compliance perspective (because adding a little lead‑free to leaded does not create a legal problem), but it can affect joint reliability and process stability.

For reflow:
- You can typically load a leaded profile and reintroduce SnPb paste after basic cleaning; residual SAC will dilute slightly but not cause legal issues.
- Verify joints by cross‑section or reliability testing for critical products.
For wave:
- If using a RoHS pot and going back to leaded, you again need to decide if you will dump and refill or accept a mixed alloy (usually not recommended for long‑term).

In most businesses, non‑RoHS production is being phased down, so the main focus is protecting RoHS, not the other way around.

6. Key Risks and How to Mitigate Them

Risk 1: Lead Contamination of RoHS Product

Issue: Tiny amounts of lead from paste, tools, or solder pots can push content above 0.1%.
Mitigation:
- Clear physical and colour separation of all materials and tools.
- “Leaded first, then RoHS” scheduling with full cleaning.
- Regular alloy and joint testing, documented cleaning procedures.

Risk 2: Mixed Alloys and Weak Solder Joints

Issue: Mixed Pb/SAC joints can form brittle intermetallic layers, cracks, and reduced reliability.
Mitigation:
- Avoid intentional mixed‑alloy joints; keep full joints either leaded or lead‑free.
- If a mixed situation is unavoidable (e.g., lead‑free paste on tin‑lead‑plated pads), optimise the profile and qualify with reliability testing.

Risk 3: Wrong Paste or Profile Loaded

Issue: Using leaded paste with lead‑free profile or vice versa can cause non‑wetting, tombstoning, or component damage.
Mitigation:
- Separate program names; lock profiles to specific product codes.
- Use checklists and bar‑code scanning for job load.
- Train operators and enforce line‑clearance audits.

Risk 4: Human Error and Poor Training

Issue: Operators accidentally use the wrong wire, paste, stencil or program.
Mitigation:
- Regular training on RoHS requirements, health aspects, and process rules.
- Visual management: big RoHS / Pb signs at each station, tool colour coding.
- Supervisor and QA spot checks per shift.

Risk 5: Incomplete Documentation for Regulators/Customers

Issue: Even if technically clean, lack of records can lead to compliance doubts or rejected PPAPs.
Mitigation:
- Maintain a RoHS control plan: material declarations, supplier certificates, process logs, test reports.
- Periodic internal audits of RoHS vs non‑RoHS process separation.

7. When to Use Separate Lines Instead

Despite careful procedures, many OEMs and EMS providers ultimately decide to physically separate RoHS and non‑RoHS once volumes justify it, because:

Changeover time and cleaning cost become high.
Risk of contamination and non‑compliance remains non‑zero.
Certification bodies and demanding customers often prefer dedicated RoHS lines.

Until then, a well‑designed mixed‑mode strategy, with strong visual management and changeover discipline, can support both product families on a single SMT line while safeguarding compliance and reliability.

Zenaca Consulting, as the authority in EMS and RoHS implementation, typically supports clients by drafting RoHS/non‑RoHS line‑separation standards, changeover checklists, and audit routines to make this mixed‑line approach robust and acceptable to global customers.