A PCB solderability test checks whether the board’s pads and plated holes still wet properly with solder after fabrication and storage. For bare boards the governing standard is IPC J-STD-003D (October 2022), which defines five methods: edge dip, wave solder, surface mount simulation and solder float, judged by eye under magnification, and the wetting balance test, which measures wetting force. Ask for it on production lots that will be stored, shipped long distances or assembled by another factory, and write the method, sample and durability category on the purchase order; a fresh prototype assembled the same week rarely needs it.
| Method | What it shows | Result |
|---|---|---|
| Edge dip (“dip and look”) | Pads and holes wet after dipping a coupon in molten solder | Visual: wetted coverage and defects |
| Wave solder | Wetting and hole fill under wave conditions | Visual |
| Surface mount simulation | Paste printed and reflowed on SMT lands | Visual |
| Solder float | Hole wetting when a coupon floats on solder | Visual |
| Wetting balance | Force and time as solder wets the specimen | Measured curve |
What Is a Solderability Test?
A controlled check of how readily molten solder wets a surface. For bare boards, J-STD-003D says its purpose is to verify that fabrication and later storage have not harmed the solderability of the areas meant to be soldered, using reference coupons or representative parts of the board processed on the same panel (J-STD-003D contents).
The scope is narrower than many buyers assume. The standard states that it does not verify that assembly will succeed and does not evaluate how the design affects wetting. A board that passes can still give poor joints from a bad stencil, paste or reflow profile. Component leads have their own test, J-STD-002; a component result does not stand in for the board, or the other way round.
Which Test Method Should You Use?
Edge dip for routine lot acceptance, wetting balance when you need numbers. Edge dip is quick and cheap: a coupon is fluxed, dipped in solder and inspected under magnification for complete wetting, dewetting and non-wetting. It needs a trained inspector but no special equipment, and it matches what most buyers want to know about a lot.
Wetting balance holds the specimen on a sensitive force gauge, dips it into solder and records the force over time. The curve shows how fast wetting starts and how strong it becomes, which makes it useful for comparing finishes, storage conditions or suppliers. The instruments are precise; one tester’s maker lists a force resolution of 0.001 mN and immersion depth control to 0.01 mm (GEN3 MUST3 brochure). Those are equipment capabilities, not pass limits; the acceptance criteria come from the standard or your specification.
Surface mount simulation is the closest to real SMT assembly, because paste is printed and reflowed on the lands. Use it when a dispute centers on SMT wetting rather than on holes.
What Is the Solder Float Test?
Two different tests share the name, so say which one you mean. In J-STD-003D, solder float is a solderability method: the coupon floats on molten solder and plated holes are checked for wetting and fill. In IPC-6012, solder float is a thermal stress test: a coupon is floated on solder (IPC-TM-650 2.6.8, typically 288 °C for 10 seconds) and then microsectioned to look for barrel cracks, separations and delamination. The second tests the plated structure, not wettability.
If the purchase order just says “solder float test”, a supplier may run either one. Write “solderability per J-STD-003D, solder float method” or “thermal stress per IPC-6012”, whichever you need.
How Do Surface Finish and Storage Change the Result?
They are the main reasons boards fail. Wettability falls as the finish ages, oxidizes or picks up contamination, and different finishes age differently. OSP and immersion finishes are the most sensitive to storage time and handling; HASL and ENIG hold up longer under good packaging. Humidity, fingerprints, sulfur-bearing packaging and repeated heat cycles all reduce wettability.
J-STD-003D rates coating durability separately from the product class. By default the rating is 2 for lead-containing finishes and A for lead-free and other finishes, and neither default requires stressing the coupon before the test. Higher durability ratings call for conditioning, such as steam exposure, before testing to simulate storage. If your boards will sit in a warehouse for months, ask for a durability rating that matches the storage time rather than the default.
Packaging carries much of the protection: vacuum-sealed bags with desiccant and a humidity indicator, and a date code on each bag. Our guide to PCB incoming inspection covers what to check when the cartons arrive.
When Should Bare Boards Be Tested?
When poor wetting would be expensive to find on the assembly line. Typical triggers:
- production lots that will be stored before assembly;
- boards shipped to a different assembly site or country;
- expensive or long-lead components on the board;
- a change of finish, laminate or supplier;
- customer or audit requirements;
- previous wetting complaints on the same part.
Test before shipment when you want the supplier to prove the lot before it leaves; test on receipt when transit and storage are the risk. For critical builds, do both on the same lot so a later dispute can be traced to the stage where wettability was lost. Prototypes assembled immediately usually do not need a formal test.
What Do Wetting Failures Look Like?
| Symptom | What it means | Likely cause |
|---|---|---|
| Non-wetting | Solder does not adhere; base metal visible | Oxidized or contaminated surface |
| Dewetting | Solder wets, then pulls back into droplets | Contamination or degraded finish |
| Pinholes and voids | Small holes in the solder coat | Outgassing, contamination |
| Poor hole fill | Solder does not rise in the plated hole | Barrel finish, contamination, thermal mass |
| Discoloration | Darkened or uneven finish before testing | Aging, handling, sulfur exposure |
A failed coupon tells you the surface is the problem; a passed coupon with bad assembly joints points to the assembly process. For ENIG boards, wetting problems on nickel are a separate issue from finish aging; our ENIG surface finish guide covers nickel corrosion.
What Should the Purchase Order Say?
| Item | Example | Why |
|---|---|---|
| Standard and method | “Solderability per J-STD-003D, edge dip” | Defines the test |
| Durability rating | “Default (A)” or a stressed rating | Sets pre-test conditioning |
| Specimen | “Coupon from each production panel lot” | Ties the result to the lot |
| Timing | “Before shipment” and/or “on receipt” | Assigns the risk |
| Report | Lot, date code, method, result, photos | Makes the record traceable |
| Packaging | Vacuum seal, desiccant, humidity indicator | Protects wettability in transit |
| Failure rule | Hold, retest or replace | Avoids arguments after the fact |
Agree on the shipment records at the same time; our guide to quality documents before shipment covers the full set, and our article on supplier qualification orders shows where a solderability check fits in qualifying a new supplier.
How Can We Help?
QueenEMS ships bare boards with the finish you specify, and for ENIG lots we measure nickel and gold thickness by XRF and can send the readings with the boards. Put the solderability method, durability rating and specimen rule on your drawing or PO, and we test coupons from the lot for solderability in house before shipment, with the result in the lot report. Quotes for bare boards are ready within 2 hours.
Conclusion
| Order | Solderability evidence |
|---|---|
| Prototype, assembled within days | Usually none beyond normal inspection |
| Production, stored or shipped far | Edge dip per J-STD-003D on each lot |
| Finish or supplier change | Wetting balance to compare against the old build |
| Long storage | Stressed durability rating before testing |
| Plated-hole reliability concern | IPC-6012 thermal stress, not a solderability test |
Name the method, the specimen and what happens if a lot fails. Contact us with the Gerber files, the finish, the test requirement and the assembly schedule.
FAQ
What is a solderability test? A check of how well molten solder wets a surface; for bare boards it follows IPC J-STD-003D.
What is the difference between J-STD-003 and J-STD-002? J-STD-003 tests printed board surfaces and holes; J-STD-002 tests component leads and terminations.
Is the solder float test a solderability test? Sometimes. J-STD-003D includes a solder float solderability method, while IPC-6012’s solder float is a thermal stress test of plated holes.
Does passing a solderability test guarantee good assembly? No. It shows the surface wets; stencil, paste, profile and components still decide the joints.
How long can bare boards be stored before solderability drops? It depends on the finish and packaging, so test after storage rather than relying on a fixed shelf life.
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