IPC PRODUCT CLASSES
Defined by IPC-A-610Acceptability of Electronic Assemblies.
| CLASS 1 | General Electronic Products Consumer products, toys. Function is main requirement. Cosmetic imperfections allowed. |
|---|---|
| CLASS 2 | Dedicated Service Electronic Products Communications, business machines. High performance and extended life required. Uninterrupted service desirable. |
| CLASS 3 | High Performance Electronic Products Military, medical, aerospace. Continued high performance or performance-on-demand is critical. Equipment downtime cannot be tolerated. |
KEY ACCEPTANCE CONDITIONS (J-STD-001)
| CONDITION | DESCRIPTION | DISPOSITION |
|---|---|---|
| TARGET | Perfect/near-perfect condition. Smooth, shiny (for SnPb), concave fillet, complete wetting. | DESIRABLE |
| ACCEPTABLE | Condition that is not perfect but ensures integrity and reliability. Minimum wetting and fillet requirements met. | ACCEPTABLE |
| PROCESS INDICATOR | Condition not affecting form, fit, or function but indicates process drift (e.g., discoloration, excess solder). | MONITOR |
| DEFECT | Condition insufficiently reliable (e.g., fracture, cold joint, non-wetting). Must be reworked. | REJECT |
IRON TIP TEMPERATURES
Recommended starting points. Adjust for thermal mass of joint.
SnPb (Leaded)
315°C - 345°C (600°F - 650°F)
Lead-Free (SAC305)
345°C - 370°C (650°F - 700°F)
Heavy Ground Planes
+30°C (+50°F)
Max Safe Temp (Pad Lift Risk)
>400°C (750°F)
ALLOY MELTING POINTS
| Sn63 / Pb37 | 183°C (Eutectic) |
| Sn60 / Pb40 | 183°C - 190°C (Plastic range) |
| SAC305 (Lead-Free) | 217°C - 220°C |
| Sn99.3 / Cu0.7 | 227°C |
THERMAL PROFILING (REFLOW)
| PHASE | TEMP RANGE | PURPOSE |
|---|---|---|
| PREHEAT | Amb → 150°C | Evaporate solvents, minimize thermal shock (~1-3°C/sec rise). |
| SOAK | 150°C → 183°C (SnPb) 150°C → 217°C (SAC) |
Activate flux, remove oxides, temperature equalization across board (60-120 sec). |
| REFLOW | Peak: 215°C (SnPb) Peak: 245°C (SAC) |
Solder melts and wets pads. Time Above Liquidus (TAL) ~60 sec. |
| COOLING | Peak → Amb | Solidify grain structure. Fast cool (2-4°C/sec) creates finer, stronger grain. |
COMMON DEFECTS & VISUAL INDICATORS
COLD JOINT
Appearance: Dull, grayish, granular/rough surface.
Cause: Insufficient heat, movement during cooling.
Process: Reflow joint with Flux.
DISTURBED JOINT
Appearance: Irregular surface, crystalline cracks.
Cause: PCB/Component moved while solder was pasty.
Process: Reflow joint.
INSUFFICIENT WETTING
Appearance: Solder balls up, does not feather out to pad edge.
Cause: Dirty pad/lead, defective flux, insufficient heat.
Process: Clean surface, check flux activity.
SOLDER BRIDGE
Appearance: Unwanted connection between adjacent pins.
Cause: Too much solder, bent pins, fast stencil release.
Process: Remove with wick/sucker.
THROUGH-HOLE FILLET CRITERIA (Class 2/3)
| FEATURE | REQUIREMENT |
|---|---|
| VERTICAL FILL | Minimum 75% vertical fill of plated through-hole (Class 2/3). |
| SOLDER SIDE FILLET | Min 75% coverage of land area. Wetting 180° - 270° around lead. |
| COMPONENT SIDE FILLET | Not required for Class 1. Evidence of flow-through required for Class 2/3. |
| LEAD PROTRUSION | Visible limit to 2.5mm max (typically). Must be discernible in solder. |
FLUX CLASSIFICATIONS
| TYPE | FULL NAME | ACTIVITY | CLEANING | USAGE |
|---|---|---|---|---|
| R | Rosin | Low | Optional | Clean surfaces only. Non-corrosive residue. |
| RMA | Rosin Mildly Activated | Medium | Recommended | Standard legacy electronics. Good wetting, residue generally safe but sticky. |
| RA | Rosin Activated | High | MANDATORY | Oxidized parts. Residue is corrosive and conductive. |
| NC / No-Clean | No Clean (Synthetic) | Low/Med | Do Not Clean | Modern SMT. Residue designed to encapsulate activators. cleaning can create white residue. |
| WS / OA | Water Soluble (Organic Acid) | High | MANDATORY (Water) | High volume wave soldering. Residue highly corrosive. Wash immediately. |
FLUX PURPOSE
- REMOVE OXIDES: Chemically strip oxidation from metal surfaces during heating.
- PREVENT OXIDATION: Coat the joint to prevent air contact during high-heat phase.
- HEAT TRANSFER: Assist in transferring heat from iron to joint.
- WETTING: Reduce surface tension to allow solder to flow (feather out).
CLEANING SOLVENTS
- IPA (Isopropyl Alcohol): >99% ideal. For R/RMA/No-Clean. (91% can leave residue).
- Deionized Water: For WS/OA flux only.
- Saponifier: Alkaline additive for water cleaning of rosin fluxes.