5.5 Solder & Flux Storage

Solder paste and flux are unique: they are among the most time-sensitive materials in electronicsthe manufacturing,factory, and their stability directly sets the stage for clean prints and reliable solder joints. Unlike metalsstatic or boards,moisture, their quality constantly degrades over time and temperature. Disciplined handling—from cold chain to thaw protocol—is essential to keep these chemistries keep changing from the moment they leave controlled storage, making the cold chain, thawing, and mixing as critical as any machine setting. Open time defines their usable life on the line, and FEFO issuing ensures the right lot runs out on schedule rather than mid-build. With disciplined handling, consumables shift from being unpredictable troublemakers to steady, repeatablepredictable contributors to yield.

5.5.1 PurposeThe &Cold scopeChain and Storage Standards

KeepThe chemistries—solderchemistry paste, liquid flux, adhesives/coatings if used—inside their safe window from dock to print/wave. This covers storage temps,rules FEFOprioritize issuing,controlling thaw/mix,the in-userate limits,of material change through temperature and clearmanaging ready/not-readyinventory checks.based Iton tiesits toremaining 5.1 (IDs), 5.2 (area controls), and 5.6 (kitting/FEFO).life.

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Storage Map: The Control Zones

5.5.2 Storage map (cold chain & friends)

Material	Where it livesLives	Temperature	NotesKey Storage Rule
Solder pastePaste (jar/cartridge)Jar/Cartridge)	CHEM-COLD fridgeFridge	Per label (typically 0–0 – 10 °˚C)	KeepMust be stored sealed &and upright. Do not freeze unless labelspecified. saysCabinets so.must Separatebe fromtemperature food/MSDs.logged.
Liquid fluxFlux (wave/selective)Wave/Selective)	Cool cabinetCabinet or CHEM-COLD if specified	15–15 – 25 °˚C unless label says otherwisespecified	Keep caps tight; avoidstore sunlight;out noof decanting to “mystery” bottles.sunlight.
Adhesives/coatingsCoatings (if used)	CHEM-COLD or coolCool cabinetCabinet	Per label	Respect pot life/UV; sensitivity. Tracktrack catalyzed mixes separately.
Solder wireWire & barsBars	CMP-STORE (dry, clean)Ambient)	Room	Flux-Wire flux-core wire has shelf life;life; keep spools bagged between uses. Bars: avoid oil/grease contamination.

Logging:

Issuing All fridges/cabinets are logged; excursions get a note and a disposition check.

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5.5.3Logic: FEFO beatsBeats FIFO

For all chemistries (issuingpaste, rules)flux,

• adhesives), the issue rule is FEFO = First Expiry, First Out.
  for paste, flux, adhesives/coatings.
• FIFOPriority: remainsKitting finemust for metals (wire/bar) unlesspick the fluxlot core has an expiry.
• Kitting pickswith the soonest-expiringsoonest expiry date lot that still has enough life for the planned usebuild +plus buffer.a buffer.
• MES showsLink: The MES/ERP must display the expiry date and days remaining atduring pick;the don’tpick process. Never override this without QEQuality Engineering (QE) sign-off.
  




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5.5.42 ThawThaw-to-Print & mix (make it printable, not sweaty)Protocol

SolderThe pastethermal transition from cold storage to the printing or soldering process is the most fragile step. Condensation is the primary risk.

Thawing Rules (The No-Condensation Zone)

1. Plan:Move Sealed: MoveTransfer the jar or cartridge from CHEM-COLD to the ambient CMP-STORE (controlledor room)kitting whilearea) while sealed in its container..
2. Thaw sealed:Time: BringAllow the material to reach full room temptemperature per jarthe sizemanufacturer's specification (typical 2–2 – 6 hhours; cartridgesfor oftenjars). 1–2Do hnot rush). Don’t rush with heatforced heat, warm water, or warma water.heat gun.
3. DewCondensation check:Check: The container must be opened only after it has reached room temperature. If the jarcontainer sweats,sweats when opened, you openedwaited too soon.long; Wipe dry; wait longer. Never open cold paste—condensation ruinshas it.ruined the paste's performance.
4. Mix:

Mixing and Readiness

• Jar:Mixing: GentlePaste must be gentle; use a hand tumble/figure-8 1–2motion minutesfor aftera thaw;jar, avoidor knead a cartridge. Avoid whipping or introducing air.
• Cartridge:Final Check: KneadBefore toprinting, uniform;the installpaste pistonmust cleanly.
• Label “IN USE” withlook Date/Timesmooth, openeduniform, and Operatorfree of separation or granules.
  

LiquidThe flux

first
• Bringprinted toboard usemust temp (label). Do not dilute unless procedure specifies; if you must, mix with documented ratios and label MIXED ON / USE BY.
  




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5.5.5 Ready/not-ready checks (before you print/solder)

Paste on printer

• Temperature: Room-temp by IR thermometer orpass the no-condensationSPI (Solder Paste Inspection) test.check for volume and height. If the print looks wrong,
• Viscosity/appearance:hold Smooth,the noline separation,and nocall granules.QE.

5.5.3 In-Use Limits and Expiry Management

Once opened, chemistries are actively degrading. Managing time and preventing contamination are the final control steps.

Open Time and Reuse

• RollOpen height:Time on Line: WithinSolder sitepaste spechas a defined open time limit on the stencil (e.g.,typically 8–124 mm).
• Test– print: First panel to SPI—volume/height within limits (see 7.x/9.x).
  

Flux at wave/selective

• Visual: Clear/consistent color; no debris.
• Flow: Spray/puddle pattern stable; no sputter.
• Test coupon: Wetting pattern acceptable.
  

If any check fails → hold and call QE. Don’t “hope-print.”




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5.5.6 In-use limits (open time & return rules)

• Solder paste open time on printer: follow label/site spec (typical 4–8 hhours). TrackThis must be tracked with a bench timer or MESthe tile.MES.
• Refresh policy:Policy: AddMaintain consistency by adding small increments of fresh paste regularly;to don’tthe pileroll/pot regularly, rather than piling fresh on top of old on oldpaste all day. Retire the rollpaste ifwhen its print quality (graping, smearing, SPI driftdrift) orbecomes graping/smearing appears.unstable.
• Jar/cartridgeReturn reuse:Ban: If re-capping, mark # of opens. Site rule example: max 2 re-opens, then scrap.
• Never return opened paste to the fridge. Keep “the "IN USE”USE" paste at room temp for theits site-defined use life (e.g., 24–24-48 h)hours), then scrap.
• Fluxscrap pot/tankit. life:Mark reusable jars/cartridges with the number of re-opens Follow(e.g., vendor/sitemax interval;2 logre-opens permitted).top-ups

Expiry and filter changes.

Adhesives/coatings: Respect pot life and UV/moisture sensitivity; discard at USE BY.

Disposition

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5.5.7 Expiry approaching or passed (what to do)

• Approaching:Near Expiry: Prioritize bythe lot using FEFO;. scheduleSchedule builds to consume.consume the material before the date.
• Just past expiry:Expired: If the date passes, HoldHOLD the lot. QE may approve a single re-qualification (e.g., a small slump/wetting/solder balling/wettingballing checkstest) or a vendor CoA extension).extension. If not requalifiedqualified the same day, the material must be scrapscrapped. 
• WellDo past expiry or unknown storage:not Scrap—don’ttrial trialexpired chemistry on customer product.
  

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5.5.84 Clean handling (keep chemistry clean)

• Use dedicated spatulasHandling and lint-freeCommon wipes;Traps no

  Preventing metal filings, oil, or hand lotion.

• Keep jar rims/cartridge tips clean; cap immediately after dispensing.
• Don’t leave containers open on benches.
• Segregate lead-free vs SnPb toolscontamination and containers;dilution color-code.
  

is

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5.5.9 Traceability (tie chemistry to the build)

• Each container has a UID (5.1) tied to lot, expiry, thaw/open times, re-opens, and disposition.
• Printers/wave machines log which lot ran each work order.
• If a defect trend appears (e.g., graping), you can pull by lot and review 5.5.5 checks.
  

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5.5.10 Acceptance cues (fast table)

Area	Accept	Reject
Cold chain	Fridge at spec; temps logged	No log; long excursions without action
Thaw	Opened only at room-temp; no condensation	Jar opened cold; water in paste
Mix	Smooth paste; cartridge kneaded; labeled IN USE	Lumpy/separated; unlabeled
Open time	Timer running; SPI stable	Guessing; SPI drift/bridging ignored
FEFO issue	Soonest expiry picked; enough lifeessential for runpredictable results.	Grabbed the newest; run ends with expired paste
Return rules	Opened paste not back to fridge	Re-chilled open jar “for tomorrow”

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5.5.11 Common traps → smallest reliable fix

Trap	Symptom	First moveMove (The Reliable Fix)
“WarmOpening itCold faster” with heat gunJar	DryCondensation edges,ruins poorthe wettingpaste; water in the jar.	No forced heatheat.; thawThaw sealed at room temp only. Scrap if condensation occurs.
Diluting flux “a little”Flux	Weak activation, solder skipsskips, or poor wetting.	No dilution unless explicitly defined in procedure; logall mixes must be logged.
Never-endingReturning paste roll	Graping, bridges by noon	Timebox open time; refresh or retire roll
Open jar to fridgeJars	Condensation ruins the paste the next dayday.	Keep “"IN USE”USE" paste at room temp;temp scrapuntil end of life; Scrap at limitlimit, never return to the fridge.
Mixing lots on one stencilLots	Inconsistent print quality across the run.	OneUse one lot per line;line/printer; requires a full stencil wipe and changeover + wipe if changingthe lot changes mid-run.
Contamination	NoPaste FEFOdegradation, metal filings, or graping.	ExpiredUse jardedicated mid-runspatulas and	lint-free wipesFEFO. inCap kitting;containers MESimmediately warnsafter on pickdispensing.

Final

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Note

on

5.5.12Traceability: PocketEach checklists

container's

BeforeUID issuing

is

• FEFOtied checked;to enough life for planned run + buffer
• Fridge/cabinet logs OK; no excursions
  

Thaw & mix

• Thawedthe sealedlot, expiry, thaw/open times, and disposition to room; no condensation
• Mixed/kneaded; jar/cartridge IN USE labeled
  

Onin the printerMES. /This wave

allows

• Open-timeyou timerto running
• Firstpull articleproduct SPI/wet-outbuilt OK
• Addwith fresha paste/fluxfailing perlot plan;if retirea whendefect drifttrend appears later.
  

End of shift

• Scrap or reseal per rule; no fridge return for opened paste
• Tanks capped; lots logged; bench wiped
  

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By storing cold, thawing carefully, mixing gently, and scrapping on time, solder paste and flux remain consistent allies instead of hidden risks. Following FEFO and clear ready/not-ready rules keeps print and wave processes stable, predictable, and defect-free.