#soldering #electronics #hakko #tools # Overview Notes on picking soldering iron tips for the bench, plus the leaded vs. lead-free question and a diagnosis of slow/balling through-hole joints. Core lesson: **for through-hole work, tip geometry matters far more than temperature setpoint.** Most "my iron isn't hot enough" problems are actually heat *delivery* problems caused by too fine a tip. Companion to [[Desoldering with HAKKO FR-301]]. # Configuration Current bench setup: | Item | Value | |---|---| | Station | HAKKO FX-888D | | Handpiece | FX-8801 | | Tip series | T18 | | Solder | Kester no-clean Sn63Pb37, 0.031" (0.8mm) | | Setpoint | 669 °F / 354 °C (as-found — see below) | Sn63Pb37 is eutectic — melts at 183 °C with no plastic range. ## Temperature setpoints Hakko's own formula ([KB 10297](https://kb.hakkousa.com/Knowledgebase/10297/What-are-the-different-optimal-soldering-temperatures-for-soldering-with-tinlead-solder-and-lead-free-solder)): > **setpoint = solder melting point + 50 °C (to make the joint) + 70–100 °C (heat reserve for thermal recovery)** The reserve term depends on station performance. The FX-888D is 936-class — 65W, ceramic heater, non-composite T18 tips — so it takes the **100 °C** reserve. Don't copy FX-951 numbers; its composite T15 tips recover better and only need 70 °C. | Solder | Melt | + 50 °C | **Setpoint** | |---|---|---|---| | Sn63Pb37 | 183 °C | 233 °C | **333 °C / 631 °F** | | SAC305 | 220 °C | 270 °C | **370 °C / 698 °F** | | SN100C | 232 °C | 282 °C | 382 °C / 720 °F | ### Per-tip adjustment Bigger tips recover faster, so they need less reserve. Extrapolated from the baseline above — start here, then tune down until joints stop completing in ~1–1.5s: | Tip | Sn63Pb37 | SAC305 | |---|---|---| | T18-D24 (2.4mm chisel — most mass) | 620 °F / 327 °C | 680 °F / 360 °C | | T18-CF2 (2.1mm bevel) | 630 °F / 332 °C | 690 °F / 366 °C | | T18-D16 (1.6mm chisel — least mass) | 645 °F / 341 °C | 705 °F / 374 °C | **Practical single setting:** 630 °F leaded, 690 °F lead-free. Covers all three tips well enough that swapping tips doesn't require touching the dial. Notes: - The as-found 669 °F was ~40 °F above the leaded baseline — warm, but *not* the cause of the balling problem. That was tip geometry. - Hakko observes most stations get left at 750 °F (399 °C) and that at that setting you don't strictly *need* to raise temp when switching to lead-free. Running lower extends tip life and reduces PCB/component damage risk. - These are **setpoints, not tip temperatures** — actual tip temp sags under load, and the FX-888D's own accuracy is roughly ±10 °C. A tip thermometer (FG-100B) is the only way to know the real number. - Sustained operation above ~400 °C accelerates plating erosion. Sleep or power down the station between sessions. # Design ## Tip shape by job | Shape | Best for | Notes | |---|---|---| | Conical / needle (B, I, BL) | Fine-pitch SMD, dense rework | Almost no thermal mass or contact area — wrong tool for through-hole | | Chisel (D) | General purpose, through-hole | Flat face contacts pad; more mass = faster recovery | | Bevel (C / CF) | Through-hole headers, drag soldering | Angled face touches pin *and* pad at once; holds a solder pool that bridges heat | | Knife (K) | Drag soldering, bridge cleanup | | `CF` variants are **tinned face only** — the unplated sides keep solder from creeping up the shank, so the bead stays on the working face. ## T18 parts list | Part | Spec | Price | Link | |---|---|---|---| | T18-D16 | Chisel, 1.6 × 14.5mm | $6.47 | [hakkousa](https://hakkousa.com/t18-d16-chisel-tip.html) | | T18-D24 | Chisel, 2.4 × 14.5mm | $6.47 | [hakkousa](https://hakkousa.com/products/soldering-iron-tips/t18-series/t18-d24-chisel-tip.html) | | T18-D32 | Chisel, 3.2 × 14.5mm | $6.47 | [hakkousa](https://hakkousa.com/products/soldering-iron-tips/t18-series/t18-d32-chisel-tip.html) | | T18-C2 | Bevel, 2.1mm / 45°, fully tinned | — | [hakkousa](https://hakkousa.com/t18-c2-bevel-tip.html) | | T18-CF2 | Bevel, 2.1mm / 45°, tinned face only | $6.47 | [hakkousa](https://hakkousa.com/products/soldering-iron-tips/t18-series/t18-cf2-bevel-tip.html) | | T18-CF3 | Bevel, 3.2mm / 45°, tinned face only | $6.47 | [hakkousa](https://hakkousa.com/products/soldering-iron-tips/t18-series/t18-cf3-bevel-tip.html) | | Kester 951 flux pen | No-clean, 2.0% solids, zero-halogen | — | [DigiKey 83-1000-0951](https://www.digikey.com/en/products/detail/kester-solder/83-1000-0951/95158) | | Hakko FS-100 | Tip cleaning / re-tinning paste | — | [hakkousa](https://hakkousa.com/fs-100-tip-cleaning-paste.html) | T18-D16 is the tip the FX-888D ships with. Full catalog: [T18 series](https://hakkousa.com/products/soldering-iron-tips/t18-series.html) — 34 shapes, $6–12 range. ## Lead-free solder — the default pick **SAC305** (Sn96.5 / Ag3.0 / Cu0.5) is the industry standard and the one to buy if only stocking one lead-free alloy. Melts ~217–220 °C, work around 370 °C. | Part | Spec | Size | Price | Link | |---|---|---|---|---| | **Adafruit #734** | SAC305, no-clean rosin core, 0.031" | **1/4 lb / 110 g** | **$29.95** | [Adafruit](https://www.adafruit.com/product/734) | | Kester 24-7068-7618 | SAC305, 275 no-clean, 0.031", 66 core (3.3% flux) | 1 lb | ~$255 | [Janel](https://www.janelinc.com/soldering-materials/kester-24-7068-7618-lead-free-275-flux-cored-solder-wire-031.html) | | Kester 24-7068-7601 | SAC305, 275 no-clean, 0.031", 58 core (2.2% flux) | 1 lb | — | [TestEquity](https://www.testequity.com/product/488SO7871-24-7068-7601) | | Adafruit #1930 | SAC305, no-clean rosin core, 0.5mm / .02" | 50 g | — | [Adafruit](https://www.adafruit.com/product/1930) | **Buy the Adafruit 1/4 lb.** Same alloy, same 0.031" diameter as the leaded spool, and 110 g is years of occasional lead-free work. The Kester 1 lb spool is the right *product* but the wrong *quantity* — $255 buys four lifetimes of solder for a bench that's mostly leaded. Skip Adafruit #1930 — 0.5mm is too fine for through-hole headers. Fine for SMD. Kester 275 flux is formulated for hand-soldering wetting performance, leaves clear residue, and is designed to reduce spatter; prefer **66 core (3.3%)** over 58 core if buying Kester, since lead-free wets poorly and extra flux directly offsets that. ## Why lead-free costs so much **Silver.** SAC305 is 3% Ag by weight, and silver price drives the spool price — this is why a 1 lb SAC305 spool runs several times a 1 lb leaded spool. The alloy-level lever is **Sn100C / Kester K100LD** (Sn99.3 / Cu0.7 + Ni) — Kester markets it literally as the "low cost alloy" because it contains no silver. Trade-offs: melts higher (~227 °C vs 220 °C), wets worse, duller joints. ==Verdict for this bench: not worth it. Buying a small SAC305 spool solves the cost problem without accepting a worse alloy. K100LD only makes sense at volume.== If revisiting, check the flux type carefully — some K100LD SKUs ship with #48 activated rosin (needs cleaning), not 275 no-clean. # Decisions - **Bevel (CF2) over chisel for headers.** The concave pool of solder the bevel holds acts as a thermal bridge across the air gap between tip and work, and the angled face contacts pin and pad simultaneously. Chisel is the safer general-purpose choice; bevel is better at this specific job. - **Don't raise temperature to fix slow joints.** It treats the symptom, burns flux faster, and shortens tip life. Fix the tip instead. - **Dedicated tips per alloy (leaded vs. lead-free).** See Troubleshooting below. Soft rule for hobby work, hard rule if anything needs to be RoHS-compliant. # Troubleshooting ## Solder balls up on the joint; takes 2–3s per through-hole pin **Cause:** solder is melting on contact with the tip, but the pad and pin never reach wetting temperature. Molten solder won't wet cold copper, so surface tension pulls it into a bead. Classic signature of a fine tip against a high-thermal-mass joint (header pin + pad + ground plane). Target is ~1–1.5s per joint. Fixes in order of impact: 1. **Bigger tip.** Chisel or bevel in the 1.6–2.4mm range. Biggest single win. 2. **Tin the tip before each joint.** A small bead bridges the air gap; a dry tip on a dry pad transfers heat terribly. 3. **Feed solder into the far side of the joint** — where pin meets pad, opposite the tip. Not onto the tip. If the joint can melt the solder, it's hot enough to wet. 4. **Add flux.** No-clean flux cores are mild and volatile; at 354 °C over a 3s dwell the flux boils off before wetting happens. 5. **Check tip condition.** Dull gray instead of shiny silver where tinned = oxidized/dewetted, won't transfer heat regardless of setpoint. Re-tin with **FS-100** paste, or replace. ## Reviving an oxidized tip (FS-100) Hakko FS-100 is a chemical paste that strips oxide and re-tins the plating. Contains no diammonium phosphate and leaves no corrosive residue. Works on badly oxidized tips that plain wire-and-sponge re-tinning won't recover. - Heat the tip to working temperature, dip into the paste briefly, wipe, then immediately tin with fresh solder. - Don't leave the tip parked in the paste — it's mildly abrasive/chemical and will thin the plating with overuse. - Can be paired with the [FT-700 tip polisher](https://hakkousa.com/ft-700-tip-polisher.html) for severe cases (FS-100 ships included with the FT-700). - **Shelf life:** Hakko nominally says one year unopened, but has observed containers up to 5 years old — opened and partially used — still cleaning effectively with only minor loss. Don't throw out an old tin on the date alone. Prevention beats revival: park the iron tinned, not bare, and turn the setpoint down (or sleep the station) between sessions. ## Leaded vs. lead-free — do I need separate tips? Ideally yes, though it's a soft rule for hobby work. - Residual solder stays in the tip's plating and wets into the next joint. Lead migrating into a lead-free joint **lowers its melting point** and can produce a weak, gritty joint. Real concern for anything RoHS-certified. - Lead-free runs hotter (~370 °C vs ~330 °C) and is more aggressive on iron plating — lead-free tips wear faster. Separate tips keep the leaded tip from getting cooked at lead-free temps. - **Also separate the sponge / brass wool** — commonly forgotten contamination path. If switching on one tip: wipe and re-tin thoroughly, and expect the first joint or two after a switch to be a blend. ## Can I use lead-free solder on a lead-HASL board? Yes, it works — but it's usually the wrong choice. **Metallurgy.** Lead from the HASL finish dissolves into the lead-free joint, creating a Sn-Ag-Cu-Pb quaternary system. The lead doesn't distribute evenly — it segregates into Pb-rich phases at grain boundaries during solidification, and those phases melt around 179 °C, well below the ~217 °C of the bulk SAC305. Under thermal cycling they become crack initiation sites, degrading fatigue life. This is the known **"backward compatibility" problem** in mixed assembly, and why aerospace/mil-spec work has explicit rules about it. **How much it matters for hand soldering:** not much. The HASL layer is thin and the wire solder dominates joint volume, so the lead fraction stays low — a few percent at most. The serious version of this problem is BGA reflow, where the ball-to-paste volume ratio differs and insufficient peak temperature leaves the joint un-homogenized. **The practical argument against:** a lead-HASL board is already not RoHS compliant — the *finish* disqualifies the assembly regardless of solder. So lead-free buys nothing on that board while costing higher working temp (~370 °C), worse wetting, a duller joint that's harder to inspect, and faster tip wear. **Reverse direction is fine.** Leaded solder on a lead-free board (ENIG, immersion tin) is standard rework practice. Same mixed-alloy caveat technically applies; nobody hesitates over it. Rule of thumb: **match the solder to the board finish when you have the choice.** # Build Log ## 2026-08-31 - Diagnosed slow (2–3s) through-hole header joints with solder balling on the pad. Root cause: very fine angled tip, insufficient heat delivery — not setpoint. 669 °F was already adequate. - Confirmed station is an **FX-888D** → FX-8801 handpiece → **T18** tip series. - Ordered T18-CF2 (2.1mm bevel, tinned face only), T18-D16 (1.6mm chisel), T18-D24 (2.4mm chisel). - Ordered Hakko FS-100 tip cleaning paste. - Worked out setpoints per tip and per alloy from Hakko's melting-point + 50 °C + reserve formula. Landing on 630 °F leaded / 690 °F lead-free as the everyday setting. - Kester 1 lb SAC305 spool priced at ~$255 — silver content, not flux or brand. Switched the lead-free recommendation to the Adafruit 1/4 lb spool ($29.95, same alloy and diameter). Considered and rejected K100LD. # TODO - ~~Confirm the actual station model~~ (done 2026-08-31 — FX-888D, T18 tips, parts list confirmed correct) - ~~Order T18-CF2~~ (ordered 2026-08-31, along with T18-D16 and T18-D24) - ==Once tips arrive: verify joint time drops to ~1.5s. Compare CF2 bevel vs. D24 chisel on the same header and record which wins.== - ==Still need a flux pen — Kester 951 not yet ordered.== - ==Decide whether to keep a dedicated lead-free tip, or stay all-leaded on this bench.== # References - [[Desoldering with HAKKO FR-301]] - [[Reflow Solder Paste]] — paste selection, reflow profiles, Reflow Master Pro - [Hakko T18 series catalog](https://hakkousa.com/products/soldering-iron-tips/t18-series.html) - [FX-8801 handpiece](https://hakkousa.com/fx8801-02-iron.html) - [FX-888DX station](https://hakkousa.com/fx-888dx.html) - [Kester 951 Flux-Pen datasheet](https://www.kester.com/products/product/951-flux-pen) - [Hakko FS-100 tip cleaning paste](https://hakkousa.com/fs-100-tip-cleaning-paste.html) - [Hakko tip cleaners catalog](https://hakkousa.com/products/accessories/tip-cleaners.html) - [Hakko KB 10297 — optimal soldering temperatures, leaded vs. lead-free](https://kb.hakkousa.com/Knowledgebase/10297/What-are-the-different-optimal-soldering-temperatures-for-soldering-with-tinlead-solder-and-lead-free-solder)