Lead-Free Soldering: SAC305, SN100C & RoHS-Compliant PCB Assembly Guide

Lead-free soldering is the process of joining electronic components to PCB pads using tin-based alloys that contain no intentional lead — the assembly standard now required for virtually every product sold into the EU, UK, China, and most regulated global markets. The dominant alloy for SMT reflow is SAC305 (Sn96.5Ag3.0Cu0.5), with a solidus at 217°C and a reflow peak of 235–250°C. For wave and selective soldering, SN100C (Sn99.25Cu0.7Ni0.05Ge) has become the go-to choice: it costs roughly 30% less than SAC305, is eutectic at 227°C, and does not corrode older solder pot steel the way silver-bearing alloys do.

The transition from Sn63/Pb37 is not a simple temperature increase. The process window is narrower, new defect modes appear that don’t exist in tin-lead processes, and RoHS compliance documentation has regulatory teeth. This guide covers alloy selection, reflow and wave profiles, the defects unique to lead-free, and the DFM rules that protect your yield from first article to volume.

Key takeaways

• SAC305 is the IPC-endorsed alloy for SMT reflow paste; SN100C is the preferred choice for wave and selective soldering at roughly 30% lower cost due to its silver-free composition.
• Lead-free reflow peaks at 235–250°C — working within a 10–20°C window above standard FR-4 glass transition (Tg 130–140°C). Moisture-sensitive parts must be pre-baked at 125°C for 4–8 hours per J-STD-033 before going into the oven.
• A dull, matte joint appearance is normal for lead-free alloys and is explicitly accepted in IPC-A-610 Class 2 and Class 3. Retouching a visually dull but dimensionally correct joint grows the intermetallic layer and degrades joint reliability.
• RoHS limits lead to 0.1% by weight (1,000 ppm) in homogeneous materials. High-lead solder exemptions covering flip-chip and server interconnects (Annex III 7(a)) are under active EU review, with most renewals expiring in 2027.
• J-STD-001 is the assembly process standard for lead-free; specifying Class 2 or Class 3 on your build spec defines inspection criteria, solder bath contamination limits, and rework tolerances — and gives your assembler a binding process reference.

What Is Lead-Free Soldering?

Lead-free soldering is an electronics assembly method that bonds components to PCB copper pads using tin-based alloys containing no intentional lead. The base metal in virtually every commercial lead-free alloy is tin (Sn), doped with combinations of silver (Ag), copper (Cu), nickel (Ni), germanium (Ge), or bismuth (Bi) to tune the melting temperature, mechanical strength, and joint appearance.

The shift away from Sn63/Pb37 is regulatory in origin. The EU’s Restriction of Hazardous Substances directive (RoHS 2011/65/EU), building on RoHS1 (2002/95/EC) which took effect July 1, 2006, limits lead to 0.1% by weight in homogeneous materials — a threshold that rules out traditional tin-lead solder entirely. That framework now extends to China RoHS (SJ/T 11364), UK RoHS, Korea’s equivalent directive, and similar legislation in dozens of other markets. Any board shipped into a regulated market requires fully lead-free assembly — compliant components, PCB surface finishes, and solder alloys — plus traceability documentation to support a compliance audit.

RoHS, REACH, and the Lead-Free Mandate: What You Actually Have to Comply With

RoHS does not simply ban lead. It restricts it to under 1,000 ppm in any homogeneous material and maintains specific exemptions for applications where no reliable lead-free alternative yet exists. For PCB assembly, three exemption categories matter most:

• Exemption 7(a) — High-lead solders (≥85% lead by weight): Permits lead in flip-chip die-attach solders, column grid array interconnects for servers, and similar high-reliability applications. The European Commission restructured this exemption in 2024–2025, splitting it into seven subcategories (7(a)-I through 7(a)-VII) with most renewals expiring between June and December 2027. If your design depends on a high-lead alloy, verify the applicable sub-exemption and current expiry date — and build a transition plan.
• Leaded component contamination: Matte-tin, tin-lead (SnPb), or JEITA alloy-code ‘1’ component terminations introduced into a lead-free assembly create a compliance problem and a reliability risk. Lead at 2% or more in a SAC305 joint alters its melting behavior and degrades thermal fatigue life. BOM review must flag non-compliant finishes before scheduling production.
• PCB surface finishes: ENIG, ENEPIG, immersion tin, and OSP are compliant by composition. Lead-free HASL — applied using SN100C or a SAC alloy — is also fully RoHS-compliant and provides a solderable shelf life exceeding one year.

For assembly process compliance, J-STD-001 (Requirements for Soldering Electrical and Electronic Assemblies) is the governing standard. For lead-free specifically, it specifies a maximum 0.1% Pb contamination in the solder bath (above this threshold the process is considered leaded under a compliance audit), flux classification requirements per J-STD-004B, and solderability testing per J-STD-003. Specifying J-STD-001 Class 2 or Class 3 on your build documentation is the binding mechanism that ties your assembler to defined process and inspection requirements.

Lead-Free Alloy Selection: SAC305, SN100C, and When to Use Each

Choosing the wrong alloy for the wrong process is the source of more lead-free line problems than any other single decision. SAC305 is not a universal replacement for tin-lead — it is the right choice for SMT reflow, and it is an expensive, maintenance-intensive choice for wave. The table below maps the five alloys you will most commonly encounter.

Alloy	Composition	Melting Point	Best Process	Typical Application	Cost vs. Sn63/Pb37
SAC305	Sn96.5Ag3.0Cu0.5	217–221°C	Reflow (paste)	SMT reflow, BGA, fine-pitch IC — the IPC-endorsed SMT standard	~2–3× higher (silver content)
SN100C	Sn99.25Cu0.7Ni0.05Ge	227°C (eutectic)	Wave, selective, bar	Through-hole wave, selective soldering, lead-free HASL — dominant wave alloy globally	~30–40% below SAC305 (no silver)
SAC0307	Sn99.0Ag0.3Cu0.7	217–219°C	Reflow (paste)	Cost-sensitive SMT where long-term thermal cycling is not critical	~15–20% below SAC305
Sn99.3Cu0.7	Sn99.3Cu0.7	227°C (eutectic)	Wave only	Budget wave. Not recommended for SMT — poor wetting without heavy flux	Lowest
Bi58Sn42	Bi58Sn42	138°C	Low-temp reflow	Heat-sensitive flex/polyimide; brittle — not for shock environments	Medium; limited availability

SAC305 — The SMT Reflow Standard

SAC305 is the alloy endorsed by the IPC Solder Value Product Council as the preferred choice for SMT paste applications and is the most widely specified lead-free paste in production globally. Its 3.0% silver content forms Cu3Sn and Ag3Sn intermetallic compounds at the joint interface, providing good thermal fatigue resistance under temperature cycling — the property that keeps it specified in automotive, industrial, and telecom SMT despite its cost. The alloy is fully defined under IPC J-STD-006 and complies with EU RoHS, REACH, and JEIDA.

The silver content that delivers thermal fatigue performance also adds roughly 30% to alloy cost versus SN100C, and makes SAC305 moderately corrosive to ferrous steel solder pot walls at wave soldering temperatures. If your wave machine predates 2010, confirm material compatibility with your alloy supplier before loading a SAC305 pot — persistent corrosion can cause a catastrophic pot failure.

SN100C — The Wave and Selective Soldering Choice

SN100C (Sn99.25Cu0.7Ni0.05Ge) was developed and patented by Nihon Superior Co. Ltd. in 1999 and is now the world’s leading alloy for lead-free wave and selective soldering, with the original patents largely expired. It is a true eutectic alloy: it melts and solidifies at a single temperature (227°C) rather than passing through a pasty range, which simplifies pot temperature control and reduces bridging tendency. The trace nickel (0.05%) suppresses copper dissolution from through-hole barrel walls and component leads into the bath. The germanium (~0.009%) reduces tin dross and improves flux wetting, which is why SN100C joints come out considerably shinier than SAC305 — an advantage for visual inspection in high-volume lines.

For wave and selective applications, SN100C’s combination of lower alloy cost (no silver), lower dross generation, reduced pot maintenance, and non-corrosive behavior makes it the default for most commercial EMS operations. The practical limitation is process temperature: SN100C’s 227°C eutectic point — 10°C above SAC305’s solidus — pushes it outside the typical SMT reflow paste window. The standard mixed-technology approach is SAC305 paste for the SMT reflow step, then SN100C bar in the wave or selective solder machine for through-hole.

Other Lead-Free Alloys Worth Knowing

SAC0307 (Sn99.0Ag0.3Cu0.7) delivers the same reflow temperature range as SAC305 with far less silver — roughly 15–20% cheaper per kilogram. Joint appearance is slightly more matte and grain structure is coarser, but for cost-sensitive consumer electronics where long-term thermal cycling is not the primary reliability driver, it is a sensible middle ground that is increasingly specified as silver prices remain elevated.

Bismuth-tin alloys (Bi58Sn42, melting point 138°C) enable peak reflow temperatures as low as 160°C, which matters for thin flex substrates, polyimide stiffeners, and heat-sensitive components that cannot survive a full SAC305 profile. The trade-off is mechanical brittleness: bismuth-tin joints fracture under impact far more readily than SAC305 and are not qualified for handheld consumer devices, automotive electronics, or any shock-stressed application.

Lead-Free Reflow Profile: Temperature, TAL, and the Failures Nobody Mentions

The lead-free reflow profile follows the same four-zone structure as tin-lead — preheat, soak, reflow, and cooling — but the temperature numbers and tolerances are significantly tighter. The reference profile for SAC305:

Stage	Temperature	Duration	Purpose / Notes
Preheat / ramp	25°C → 150°C at 0.5–2°C/s	60–90 s	Evaporate surface moisture; limit thermal shock to board and components
Soak / flux activation	150–190°C	60–120 s	Activate flux chemistry; outgas volatiles before peak; equalize delta-T across board. Do not exceed 120 s — longer soak exhausts flux and causes graping.
Reflow / peak	Peak 235–250°C (SAC305 solidus 217°C)	45–90 s TAL	Fully liquefy SAC305; form Cu3Sn / Ag3Sn intermetallics at pad interface; wet component terminations. Standard FR-4 Tg 130–140°C is well exceeded at this stage — use high-Tg laminate for boards with 2+ reflow passes.
Cooling	Peak → ambient at 3–6°C/s	—	Faster controlled cooling produces finer grain structure and higher joint fatigue strength. Do not slow-cool to “fix” appearance — slow cooling coarsens grains.

Three Things Engineers Get Wrong With Lead-Free Reflow

The peak temperature window is a cliff in both directions. SAC305 needs a peak of 235–250°C to fully wet. Standard FR-4 (Tg 130–140°C) is already well above glass transition at that temperature; you are accumulating z-axis CTE stress with every pass. High-Tg laminates (≥170°C) give you meaningful additional margin and are worth specifying for boards that will see more than two reflow passes or for mixed-technology boards with a second selective soldering step. On the component side, J-STD-020 MSL ratings typically allow 260°C for 10 seconds max — only 10–15°C above your reflow peak, with zero margin for a local hot spot. Pre-bake all moisture-sensitive parts at 125°C for 4–8 hours before the oven.

The delta-T across the board must stay below 10°C during reflow. A large copper ground pour on one side and a fine-pitch BGA on the other do not heat at the same rate. When the component-dense end reaches peak and the ground plane area is still 10°C below liquidus, you get either incomplete joints or thermally over-stressed packages. Characterize your profile with a thermocouple data logger at a minimum of five zones across the production board before releasing to volume. This is not optional for lead-free production.

Extending the soak to “make sure the flux activates” often produces the opposite result. Here is the counterintuitive part: a soak zone longer than 120 seconds exhausts the flux before the board ever reaches peak temperature. Once flux chemistry is consumed, the thin oxide layer on SAC305 solder particles — and on BGA solder balls — is no longer actively reduced during reflow. The result is graping defects on passives and head-in-pillow defects on BGAs. The soak should be the minimum duration needed to equalize delta-T across the board, not a safety margin.

When Nitrogen Atmosphere Helps — and When It Doesn’t

Running reflow under a nitrogen (N2) blanket reduces surface oxidation at peak temperature and genuinely improves wetting on BGA assemblies and fine-pitch work, particularly where boards have been stored longer than 24 hours after printing. It is worth the operating cost on high-density SMT lines. The part most articles skip: nitrogen does not fix a flawed profile. If the soak is exhausting the flux or the peak is 5°C low, adding N2 extends the workable window only marginally. Fix the profile first; then evaluate nitrogen as a yield optimization for your most challenging assemblies.

Lead-Free Wave and Selective Soldering: Process Differences That Matter

Lead-free wave soldering runs a solder pot at 255–265°C for both SAC305 and SN100C — roughly 10–15°C above the equivalent tin-lead operation. That temperature increase raises energy consumption modestly, but its primary consequence is accelerated copper dissolution from PCB through-hole barrel walls and component leads into the bath. In a SAC305 pot, copper levels above 0.95% raise the bath liquidus and force either a temperature increase or a bath correction. Regular ICP or OES bath analysis — every two to four weeks in active production — keeps copper in spec.

SN100C’s nickel addition specifically targets copper dissolution. Nickel competes with copper for dissolution sites on the pot walls and component surfaces, reducing the pickup rate and extending the interval between bath corrections. For high-throughput lines running 200 or more boards per day, the maintenance savings justify the switch from SAC305 wave to SN100C even before factoring in the alloy cost difference.

Selective soldering — where a precision nozzle wets individual through-hole pads without exposing the whole board to a wave — is the correct approach for mixed-technology boards where SMT components sit close to through-hole pads that would not survive wave thermal exposure. Both SAC305 and SN100C are used in selective applications; the common production approach is SAC305 paste for SMT reflow, then SN100C bar in the selective machine. Running the same alloy through both wave and selective steps reduces contamination tracking and simplifies bath management.

For hand soldering and rework, set the iron to 330–360°C as a starting point for SAC305 or SN100C wire. The reflex to increase temperature when lead-free wets more slowly than Sn63/Pb37 is wrong: higher temperature accelerates tip oxidation, dissolves iron from the tip into the molten tin, and reduces tip life — which is already significantly shorter in lead-free service than in leaded. Use a chisel or bevel tip with more thermal mass, and re-tin the tip every three to four joints to prevent oxide buildup.

Lead-Free Soldering Defects: What’s Different and Why

Lead-free assembly introduces defect modes that are either rare in Sn63/Pb37 processes or unique to high-tin alloys. Knowing the mechanism is what separates a permanent fix from a temporary patch.

Dull Joints Are Not Cold Joints

This is the most common misdiagnosis on a line moving from leaded to lead-free. A correctly formed SAC305 joint is slightly dull, matte, and may show a faintly grainy surface texture. All of this is normal — a result of the alloy’s coarser grain structure compared to tin-lead — and IPC-A-610 explicitly accepts it for both Class 2 and Class 3 hardware. Retouching a joint because it looks dull grows the Cu3Sn intermetallic layer at the pad interface with each thermal cycle, progressively reducing fatigue life. When evaluating lead-free joints, inspect fillet shape and wetting angle first; evaluate appearance last.

Graping and Head-in-Pillow Under BGAs

Graping is incomplete coalescence of solder paste: individual powder particles partially fuse but do not collapse into a homogeneous joint. It appears as a lumpy, granular surface finish on two-terminal passives and is caused by flux exhaustion during a prolonged or high-temperature soak. By the time the paste reaches reflow peak, insufficient active flux remains to reduce the thin oxide on each particle and allow wetting. The fix is a soak calibrated to the minimum duration needed for thermal equalization, not a fixed safety margin, combined with Type 4 or 5 paste for very fine pitch work.

Head-in-pillow (HiP) is graping’s counterpart in BGA and CSP joints. As the package heats through the reflow profile, package warpage lifts the outer rows of BGA solder balls off the printed paste before peak temperature is reached. If the flux on the paste has been depleted during a long soak, when those balls reconnect with the paste at peak, both surfaces are oxidized — they melt in isolation and touch without coalescing. The resulting joint has no metallurgical bond and will pass ICT and functional test but fail under vibration or thermal cycling in the field. Standard 2D X-ray inspection does not reliably detect HiP; automated X-ray inspection (AXI) with cross-section capability or 3D CT scanning is required for confirmation on BGA-heavy Class 3 assemblies.

Tin Whiskers

Tin whiskers are crystalline filaments that grow spontaneously from high-purity tin surfaces — component lead terminations, matte-tin platings, and some SAC alloy surfaces. They range from a few microns to several millimeters in length and can bridge adjacent pads to cause intermittent shorts. In tin-lead soldering, the 2–5% lead addition suppresses whisker nucleation by introducing compressive stress relief in the tin lattice. Without lead, that suppression mechanism is gone. The mitigation hierarchy for IPC-A-610 Class 3 hardware: specify components with a nickel underlayer beneath bright (electrolytic) tin plating, which itself introduces the compressive stress that inhibits whisker nucleation; apply conformal coating post-assembly to encapsulate any filaments that do form; and avoid pure matte-tin finishes on component leads for long-life, high-reliability applications.

Voiding Under BGAs and QFNs

Lead-free solder produces higher void percentages under BGA balls and QFN thermal pads than tin-lead, primarily because flux volatiles outgas through the joint during reflow. A ramp from soak to peak that exceeds 2°C/s traps those volatiles before they can escape, and they nucleate voids as the joint solidifies. Void area percentages above 25% under BGA balls (per IPC-7095 guidance) reduce joint fatigue life under thermal cycling and introduce resistance variation in high-current paths. A 5°C reduction in peak temperature combined with extending TAL from 45 to 70 seconds typically reduces BGA void rates by 20–30% on a given board design — a meaningful yield lever that costs nothing but profile calibration time.

Lead-Free Soldering DFM Checklist: 10 Actions Before You Release Your Gerbers

Here is the truth about lead-free yield: the cheapest defect is the one your design prevents. An industrial controls manufacturer we worked with shipped an initial 3,000-unit production lot before field returns started revealing sporadic board failures. Post-mortem identified head-in-pillow defects on a 0.8 mm pitch BGA — traced to a 95-second soak zone on a board with a large copper ground pour, a profile inherited from the leaded predecessor product without requalification. A 15-minute profile optimization on the oven eliminated the defect mode entirely. No hardware redesign, no component change, no material cost.

1. Specify the solder alloy explicitly on the assembly drawing. “Lead-free” is not a process specification; “SAC305 per IPC J-STD-006” is. Without an explicit alloy call-out, your assembler will select the cheapest compatible alloy for the process.
2. State your IPC-A-610 acceptance class (Class 2 for commercial/industrial, Class 3 for high-reliability) on the assembly drawing before releasing the BOM. Class 3 adds 15–30% to inspection cost and tightens joint acceptance criteria, including maximum allowable void area percentages.
3. Audit your BOM for MSL compliance before scheduling production. Flag all parts with floor-life limits and require assembler pre-bake documentation at 125°C for 4–8 hours per J-STD-033. Un-baked MSL parts can delaminate (“popcorn crack”) in the oven during lead-free reflow.
4. Specify high-Tg laminate (≥170°C Tg) for boards that will see more than two reflow passes, or for mixed-technology boards with a separate selective soldering step. Standard FR-4 (Tg 130–140°C) accumulates z-axis CTE stress that can crack microvias and via barrels under repeated thermal excursions through the SAC305 peak zone.
5. Window all QFN and large exposed thermal-pad apertures. Print 100% paste under a QFN thermal pad and the part floats on a solder pool during reflow, lifting perimeter leads. A 50–70% windowed grid aperture controls void area and keeps the part coplanar.
6. Fill and cap all via-in-pad structures per IPC-4761 Type VII. Open vias under SMT pads wick solder away from the joint during reflow and starve it. This failure mode is invisible until the board is cross-sectioned.
7. Add local fiducials adjacent to BGA, CSP, and fine-pitch QFP footprints in addition to global board-corner fiducials. Local fiducial registration reduces BGA placement error from the typical ±75 μm to ±25 μm or better on the placement machine.
8. Segregate all leaded component finishes in your BOM. Flag any part coded with matte-tin, tin-lead (SnPb), or JEITA alloy code ‘1’ terminations. Lead contamination above 0.1% Pb in the assembled joint creates both a RoHS non-conformance and a reliability risk from altered alloy melting behavior.
9. Include a maximum 0.1% Pb solder bath specification on your work order. Above this threshold the process can be challenged as a leaded assembly under a RoHS compliance audit.
10. Require first-article inspection (FAI) documentation that includes a reflow profile chart with thermocouple traces from at least five board locations, an SPI pass rate summary, and AOI/X-ray results. This is your baseline process qualification evidence for compliance audits and field failure investigations.

Frequently Asked Questions About Lead-Free Soldering

Is SAC305 RoHS-compliant?

Yes. SAC305 (Sn96.5Ag3.0Cu0.5) contains no lead, cadmium, mercury, or other restricted substances above RoHS threshold levels. It is fully compliant with EU RoHS 2011/65/EU, UK RoHS, China RoHS (SJ/T 11364), and REACH, and it meets IPC J-STD-006 alloy specification requirements. It is the most widely specified lead-free solder alloy in global PCB assembly.

Can I mix leaded and lead-free solder on the same board?

You can produce such a board, but it creates both compliance and reliability problems. Lead introduced into a SAC305 joint at 2% or more alters the alloy’s melting behavior and degrades thermal fatigue life by disrupting the Cu3Sn/Ag3Sn intermetallic layer. More critically, a board with any leaded joints is not RoHS-compliant and cannot be sold into regulated markets without specific documented exemption. Mixed builds require engineering disposition, controlled lot segregation, and process separation between leaded and lead-free lines.

What temperature should I set my soldering iron for lead-free solder?

A starting point of 330–360°C covers SAC305 and SN100C wire. The more important variable is tip geometry and thermal mass: a chisel tip at 340°C transfers more heat per second to a large ground pad than a conical tip at 380°C. Per IPC-7711/7721, the target is the minimum temperature that allows you to complete the joint in 3–5 seconds. Cranking the iron hotter to compensate for slow wetting accelerates tip oxidation and iron dissolution, reducing tip life — which is already substantially shorter in lead-free service than in leaded.

Why do lead-free solder joints look dull — is that a defect?

No. The dull, slightly matte surface finish of SAC305 and SN100C joints is a result of their coarser grain structure compared to Sn63/Pb37 — not a process defect. IPC-A-610 explicitly accepts this appearance for both Class 2 and Class 3 hardware. Inspect joints for fillet geometry, wetting angle, and voiding; do not rework a joint solely because it looks dull. Unnecessary rework grows the intermetallic layer at the pad interface with each thermal cycle and weakens the joint.

Are there still RoHS exemptions for leaded solder?

Yes, for specific applications. EU RoHS Annex III Exemption 7(a) permits lead in solder alloys with ≥85% lead by weight, used primarily for flip-chip die attach and column grid array interconnects in servers and telecom infrastructure. The EU Commission restructured this exemption into seven subcategories in 2024–2025, with most renewals expiring in mid-to-late 2027. If your product design depends on a leaded exemption, verify the current applicable sub-exemption, document it in your technical file, and begin qualification of a lead-free alternative.

What does J-STD-001 require for lead-free assembly?

J-STD-001 specifies: maximum 0.1% Pb contamination in the solder bath, process temperatures appropriate for the specified alloy, flux classification requirements per J-STD-004B, and solderability testing per J-STD-003. Assemblers claiming J-STD-001 compliance must document their flux classification, solder alloy certificates of conformance, and process qualification data. Specifying J-STD-001 Class 2 or Class 3 on your build documentation binds your assembler to those requirements and provides the inspection criteria reference for receiving inspection.

What is the difference between SN100C and SAC305 for wave soldering?

For wave and selective soldering, SN100C has four concrete advantages over SAC305: it costs roughly 30% less per kilogram (no silver), it does not corrode older ferrous steel solder pot walls the way silver-bearing alloys can, its germanium addition significantly reduces dross generation and the labor cost of pot maintenance, and its nickel addition suppresses copper dissolution from through-hole barrel walls extending bath service life. SAC305 is still specified in some wave applications where its silver-bearing thermal fatigue performance is needed; for most commercial production volume, SN100C’s total cost of ownership advantage is decisive.

Getting Lead-Free Assembly Right From the First Build

Lead-free soldering rewards upfront preparation and penalizes improvisation. The engineers who run clean lead-free lines are the ones who treated the process change as a full qualification event: they selected the right alloy for each process stage, profiled the reflow oven with a thermocouple logger, pre-baked all MSL parts, stated J-STD-001 Class 2 or 3 explicitly in the build spec, and required first-article documentation before approving volume production. The programs that generated post-shipment field failures were the ones that assumed lead-free was just “a temperature bump” and inherited graping, head-in-pillow, voiding under QFNs, and tin whisker risk — a defect vocabulary they had never needed before.

If you are preparing a new design for lead-free PCB assembly or converting an existing leaded product, send your Gerbers and BOM for a free DFM review — we will identify MSL conflicts, thermal pad sizing issues, via-in-pad concerns, and surface finish incompatibilities before your first production run.