#soldering #reflow #solder-paste #smd #electronics #chipquik # Overview Solder paste selection for the Reflow Master Pro oven setup and the 190 °C hot plate. Standardized on the **Chip Quik TS391 "Thermally Stable"** family across all three alloys — the whole point being one storage story (no refrigeration, no warm-up) instead of per-paste handling rules. Companion to [[Soldering Iron Tip Selection]] (hand soldering, iron tips, wire solder). ==The single most important thing on this page is the 96 °C Sn-Bi-Pb hazard under Troubleshooting.== # Configuration | Item | Value | |---|---| | Reflow controller | Unexpected Maker **Reflow Master Pro** (ESP32-S2, 2x MAX31855, dual K-type TC) | | Profiles | 5 built-in + custom via built-in webserver; Classic or PID algorithm | | Hot plate | 190 °C max — used standalone for low-temp work | | Current paste | Chip Quik **TS391AX** (Sn63/Pb37, T4, 15g syringe) | Oven guidance from Unexpected Maker: **≤18 L capacity, ≥1300 W**. Too big or underpowered and the oven can't reach soak temperature in time to stay inside the paste manufacturer's profile. # Design ## Alloy comparison | Alloy | Melts | Peak reflow | Works on 190 °C hot plate? | |---|---|---|---| | Sn42/Bi57.6/Ag0.4 (low temp) | 138 °C | ~165–180 °C | **Yes** — comfortably | | Sn63/Pb37 (leaded) | 183 °C | ~210–225 °C | **Yes** — proven in practice | | SAC305 (lead-free) | 217–220 °C | ~235–245 °C | **No** — hot plate is below the melting point | ## Chip Quik TS391 Thermally Stable family All T4 mesh (20–38 µm), synthetic no-clean, ROL0, **no refrigeration required**, shelf life >12 months refrigerated *or* unrefrigerated, no warming time before use. | Part | Alloy | Melt | Metal % | Package | Link | |---|---|---|---|---|---| | **TS391AX** | Sn63/Pb37 | 183 °C | 88% | 15g / 5cc syringe | [Chip Quik](https://www.chipquik.com/store/product_info.php?products_id=470011) · [datasheet](https://www.chipquik.com/datasheets/TS391AX.pdf) | | **TS391LT** | Sn42/Bi57.6/Ag0.4 | 138 °C | 90% | 15g / 5cc syringe | [DigiKey](https://www.digikey.com/en/products/detail/chip-quik-inc/TS391LT/7802220) | | **TS391LT50** | Sn42/Bi57.6/Ag0.4 | 138 °C | 90% | **50g jar** | [Chip Quik](https://www.chipquik.com/store/product_info.php?products_id=470010) · [datasheet](https://www.chipquik.com/datasheets/TS391LT50.pdf) | | **TS391SNL** | SAC305 | 217–220 °C | 87% | 15g / 5cc syringe | [Chip Quik](https://www.chipquik.com/store/product_info.php?products_id=470001) | | **TS391SNL50** | SAC305 | 217–220 °C | 87% | 50g jar | [Chip Quik](https://www.chipquik.com/store/product_info.php?products_id=470005) | **Package matters:** the `50` suffix is a **50g jar** — stencil-printing packaging. Syringes (15g / 5cc) are for hand dispensing. Jar is cheaper per gram but useless without a stencil setup. Standard (non-TS) Chip Quik lines exist in the same alloys at lower cost — the [440xxx low-temp series](https://www.chipquik.com/store/product_info.php?products_id=440001), etc. ==Not worth it: they give up the no-refrigeration property, which is the entire reason to be in the TS391 family.== # Decisions - **Stay in the TS391 Thermally Stable family for every alloy.** One storage rule for the whole bench: room temperature 20–25 °C, use straight from the drawer. Mixing in refrigerated pastes means remembering which syringe needs 4 hours on the bench before it prints. - **Low temp = TS391LT, not the 440xxx series.** Recommended by a friend, and correct — same alloy, but keeps the no-fridge property. - **SAC305 is oven-only.** The hot plate physically cannot reflow it. Accepting that is the cost of going lead-free. - **T4 mesh throughout.** Matches TS391AX, so dispensing and stencil behavior stays familiar across alloys. # Troubleshooting ## ⚠ Never rework SnBi joints with leaded solder — 96 °C hazard **Sn-Bi-Pb forms a ternary eutectic at roughly 96 °C.** Touch a Sn42/Bi57.6/Ag0.4 joint with Sn63/Pb37 wire and the resulting joint can soften below the boiling point of water. In a warm enclosure, a car interior, or next to a regulator, that joint fails silently. - Rework SnBi with SnBi. Rework leaded with leaded. - If mixing is unavoidable, **remove the original solder completely** (wick/vacuum) before adding the other alloy. - This is invisible — no visual cue that a joint has become low-melting. Label boards, or standardize per-project. Relevant here specifically because leaded wire solder and low-temp paste both live on this bench. ## SnBi reliability limits Sn42/Bi57.6/Ag0.4 is **brittle**. Poor thermal-cycling and drop-shock performance compared to SnPb or SAC305. Also behaves badly if it ends up mixed with SAC surface finishes. Fine for: prototypes, shelf-queen boards, heat-sensitive components, anything where the 138 °C melt saves a part from cooking. Not for: anything handled, vibrated, dropped, or thermally cycled. ## Thermocouple temperature limit Unexpected Maker recommends a **glass-shielded thermocouple for pastes above 190 °C**, because standard probe shielding isn't guaranteed to survive the 200 °C+ reflow requires. The stock RMP K-type probes are fine for most use but were not specified with SAC305 peaks in mind. Suggested upgrade: [Adafruit #270](https://www.adafruit.com/product/270) (metal/fiberglass shielded). Also helps with RF noise pickup in the readings. ## Hot plate can't reach SAC305 Not a "works poorly" situation — 190 °C is *below* SAC305's 217 °C melting point. Nothing reflows. Low-temp SnBi is the only lead-free alloy the hot plate can run. ## Grounded hot plate + thermocouple Commercial / AC-powered hot plates are usually grounded, so a thermocouple connected directly to the plate will throw a read error on the RMP. Fix: attach the TC with **thermal tape** — heat transfer without electrical continuity. # Build Log ## 2026-08-31 - Researched lead-free paste options for the Reflow Master Pro. - Initially picked TS391SNL for SAC305 — still correct for oven work. - ==Correction:== first low-temp recommendation was the standard 440xxx line. Friend flagged **TS391LT50** as his preference; verified it's the better product (Thermally Stable family, keeps the no-refrigeration property). Adopted. - Documented the Sn-Bi-Pb 96 °C ternary eutectic hazard. # TODO - ==Decide: TS391LT (15g syringe, hand dispensing) vs TS391LT50 (50g jar, stencil). Depends on whether a stencil workflow is happening — syringe is the safer default for now.== - ==Check whether the stock RMP thermocouples are glass-shielded before attempting any SAC305 profile. Order Adafruit #270 if not.== - ==Build/verify a SAC305 reflow profile on the RMP (~245 °C peak) from the Chip Quik datasheet. Check whether one of the 5 built-ins already covers it.== - ==Run the RMP oven ramp test before trusting it at 245 °C — leaded profiles peak ~35 °C lower and may have been hiding a marginal oven.== # References - [[Soldering Iron Tip Selection]] - [Reflow Master Pro docs](https://help.unexpectedmaker.com/docs/products/reflow-master-pro/) · [product page](https://www.tindie.com/products/seonr/reflow-master-pro/) · [reflowmasterpro.com](https://reflowmasterpro.com/) - [ReflowMaster on GitHub](https://github.com/UnexpectedMaker/ReflowMaster) - [Chip Quik TS391AX datasheet](https://www.chipquik.com/datasheets/TS391AX.pdf) - [Chip Quik TS391LT50 datasheet](https://www.chipquik.com/datasheets/TS391LT50.pdf)