Article 3 Core Processing and Quality Control Requirements of IPC-A-600 Class 2
This Article sets out the mandatory standards for Party B's production, self-inspection and outgoing inspection. All products must meet the following core Class 2 commercial-grade requirements:
3.1 Base Material Appearance and Performance Requirements
3.1.1 The base material shall be free of fatal defects such as delamination, blistering, cracks, burns, carbonization and through-penetrating scratches, and shall contain no internal impurities or voids, meeting the Class 2 requirements for base material integrity.
Standard:
- A. Board-edge nicks or edge damage smaller than 2.54 mm, and not exceeding 50% of the distance between the board edge and the adjacent conductor;
- B. Pits and micro-craters with a diameter of less than 0.075 mm, not exceeding 5% of the board area: accepted for Class 1. Where the defective area on the two sides is ≥10%, Classes 1, 2 and 3 are all scrapped;
- C. Delamination/blistering: not exceeding 1% per side, not exceeding 25% of the distance between two adjacent conductors and plated-through holes, and with a distance to the board edge greater than 2.5 mm;
- D. Inclusions within the base material: transparent inclusions are accepted; for other particles, length ≤0.8 mm, distance to the nearest conductor ≥0.13 mm, and the minimum spacing between two conductors must not be reduced.
3.1.2 Slight stains, shallow scratches, color differences or localized slight oxidation on the board surface that do not affect insulation performance, mechanical strength, electrical continuity or subsequent assembly and use are judged acceptable under Class 2; deep scratches, base material damage or large-area oxidation and corrosion are nonconforming.
3.1.3 The heat resistance, insulation and voltage withstand performance of the board material shall conform to the corresponding material specifications and the IPC-A-600 Class 2 reliability requirements; base material performance shall be consistent within a batch, with no batch-wide performance anomalies.
3.2 Conductor (Copper Foil and Trace) Quality Requirements
3.2.1 Traces shall be free of functional defects such as opens, shorts, nicks, breaks and severe copper shrinkage; line width and spacing tolerances shall be within the deviation range permitted by the drawings and the Class 2 standard.
Standard:
the customer-designed line width may be increased or reduced by ≤20% (rough line edges, thinned lines, nicks, pinholes, scratches exposing the base material, etc.); however, such reduction must at no time exceed 10% of the line length.
Line spacing: a spacing reduction not exceeding 20% is accepted for Classes 1, 2 and 3; a spacing reduction of ≥20% but not exceeding 30% is rejected for Class 3 and accepted for Classes 1 and 2.
3.2.2 Trace edges with slight roughness, slight burrs or localized slight copper foil unevenness that do not exceed the IPC-A-600 Class 2 permitted tolerances and do not affect conductivity or insulation spacing are judged acceptable.
| Outward burr / protrusion |
≤10% of line width |
| Inward line-width loss |
≤20% of line width; total defect length must not exceed 10% of the trace length, and must not exceed 13 mm |
| Trace edge roughness |
≤2μm |
3.2.3 Defects such as missing traces, large-area exposed substrate, lifted or peeled copper foil, and out-of-tolerance trace shift are prohibited; any such problem is uniformly judged nonconforming.
3.3 Hole Diameter and Hole Wall Quality Requirements
3.3.1 The diameter tolerance and position accuracy of mechanical holes, via holes and pad holes shall conform to the drawings and the IPC-A-600 Class 2 standard, with no plugged holes, missing holes or out-of-tolerance off-center holes.
A. Hole position tolerance: Class 1: ±0.1 mm Class 2: ±0.075 mm Class 3: ±0.05 mm
B. Hole-to-pad concentricity: judged by minimum annular ring width. Class 2 hard requirements: minimum remaining annular ring on outer-layer pads ≥0.05 mm, with 90° breakout permitted; minimum remaining annular ring on inner-layer pads ≥0.025 mm.
C. Hole wall perpendicularity (hole skew / drill deviation): maximum hole wall tilt offset ≤5% of the board thickness (e.g., board thickness 1.6 mm × 0.05 = 0.08 mm).
D. Slots (oblong holes): PTH plated slots: finished slot width tolerance is the same as that of the corresponding hole diameter; slot length tolerance ±0.15 mm.
NPTH non-plated slots: slot width ±0.10 mm; slot length ±0.2 mm.
3.3.2 Slight hole wall roughness, slight copper residue or localized minor blemishes that do not affect component insertion, soldering or electrical continuity meet the Class 2 requirements.
Hole wall roughness: Class 1: ≤35 μm Class 2: ≤25 μm Class 3: ≤20 μm
3.3.3 Defects such as hole wall cracking, hole copper fracture, delamination, out-of-tolerance hole deformation, and batch-wide plugged or missing holes that affect use are prohibited.
Plating thickness in holes is as follows:
| Average minimum thickness (μm) |
≥18 |
≥20 |
≥25 |
| Thinnest area (μm) |
15 |
18 |
20 |
Hole diameter tolerances are as follows:
| ∮0.7-0.8㎜ |
±0.10 |
±0.075 |
±0.05 |
∮0.4-0.8㎜ |
±0.08 |
±0.05 |
±0.03 |
| ∮0.85-1.6㎜ |
±0.15 |
±0.10 |
±0.075 |
∮0.85-1.6㎜ |
±0.10 |
±0.075 |
±0.05 |
| ∮1.65-6.3㎜ |
±0.20 |
±0.15 |
±0.10 |
∮1.65-6.50㎜ |
±0.15 |
±0.10 |
±0.08 |
3.4 Solder Mask Ink Quality Requirements
3.4.1 The solder mask shall cover the board evenly, with no fatal defects such as exposed copper, pinholes, large-area peeling, blistering, cracking or contamination of pads, and its insulating and protective performance shall be up to standard. Exposed copper beyond the permitted range, solder mask peeling, and batch-wide blistering are nonconforming defects.
Standard:
- A. Isolated tiny bubbles/pinholes are acceptable (single diameter ≤0.15 mm; must not span two conductors or bridge traces). Not accepted: burst bubbles (a burst = exposed copper), bubbles >0.3 mm, bubbles in clusters or joined patches, bubbles spanning adjacent traces, and burst bubbles exposing copper.
- B. Any true exposed copper (bare copper metal) on traces or copper areas is rejected on sight; if the solder mask is intact and only shows light through or a faint copper tone (false copper exposure / yellowing at hole openings / ink not broken), it is acceptable.
- C. Spot exposure of base material: isolated small spots that do not cross traces and are few in number are a process warning and acceptable; large-area exposed base material is rejected.
- D. Slight ripples or orange peel are acceptable provided there are no cracks or lifting, the insulating protection is not reduced, and assembly is not affected; not accepted: solder mask cracking, wrinkling or lifting, and creases causing local thinning or damage.
3.4.2 Slightly uneven solder mask edges, localized slight thickness variation, minor color differences and slight exposed substrate in non-functional areas that do not affect insulation, moisture resistance, oxidation resistance or solderability meet the Class 2 acceptance standard.
Standard:
- A. Slight serrations on the solder mask edge are permitted, but must not form a conductive path or reduce electrical clearance.
- B. Residual ink on pads is rejected, as it affects soldering.
- C. Slight color differences within the same board are permitted; localized blackening or oxidation is not permitted.
- D. Surface foreign matter: acceptable if non-conductive, not reducing electrical clearance and not embedded within the solder mask; conductive foreign matter is not accepted.
3.4.3 Solder mask registration offset: Standard: A. The solder mask must not encroach on effective soldering areas (SMT pads, BGA pads). Permitted offset: ≤0.075 mm (3 mil), but the bottom line is that the solderable area of the pad must not be reduced; if ink lands on the soldering area of a pad, it is rejected outright.
B. PTH annular ring: after solder mask offset, the remaining annular ring width must still meet the design minimum annular ring width.
C. Solder dam (solder mask between two pads/traces): minimum retained width ≥0.07 mm, to prevent short-circuit risk.
3.4.4 Solder mask ink thickness: Standard: Class 1: complete coverage by visual inspection; Class 2: ≥10 μm; Class 3: ≥17.5 μm (base material 30–40 μm; conductors and corners 10 μm).
3.4.5 Via tenting and plugging processes: Standard: A. Via tenting: the solder mask fully covers the hole opening; slight yellowing or reddening at the hole opening (false copper exposure: thin ink with copper color showing through) is not true copper exposure and is acceptable. Not accepted: cracked or holed solder mask at the hole opening, true copper exposure (bare copper metal), large-area solder mask collapse, and open hole openings.
B. Solder mask plugging: for double-sided solder mask plugging, ink fill in the hole must be ≥70%; completely empty holes are not permitted; under X-ray, no through-going large voids are permitted.
C. Surface unevenness at the hole opening: recess depth ≤50 μm (0.05 mm); protrusion ≤50 μm and must not interfere with component placement; ink at the hole opening flowing outward onto adjacent traces/pads is acceptable only where it does not cause a defect.
3.5 Legend (Silkscreen) Quality Requirements
3.5.1 Legends, markings and model numbers on the board shall be clear and legible, with no wrong prints, missing prints, double prints or inverted characters, meeting the needs of product identification and traceability.
3.5.2 Slightly blurred legends, slight misregistration or localized slight incompleteness that does not affect manual or machine recognition meet the IPC-A-600 Class 2 commercial standard.
3.5.3 Defects that affect product traceability and use, such as completely illegible legends, wrong markings and garbled characters, are judged nonconforming.
3.6 Surface Finish and Pad Quality Requirements
3.6.1 All surface finishes (OSP, ENIG, HASL, immersion silver, etc.) shall have uniform plating, with no defects such as missing plating, plating loss, blackening, severe oxidation, pinholes or peeling; solderability and corrosion resistance shall meet commercial-use requirements.
3.6.2 Slight color differences on pads or localized minor plating unevenness that do not affect solder joint strength or electrical continuity meet the Class 2 judgment requirements.
3.6.3 Large-area oxidation, plating loss, contamination or deformation of pads that prevents normal soldering or results in poor continuity is uniformly judged nonconforming.
3.7 Outline and Dimensional Tolerance Requirements
3.7.1 Outline cutting, routing and chamfering shall conform to the dimensions in the drawings, and overall dimensions, hole-to-hole spacing and outline tolerances shall strictly follow the range permitted by IPC-A-600 Class 2.
3.7.2 Slight edge burrs or slight sanding marks that do not affect assembly or appearance in use are judged acceptable.
3.7.3 Outline deformation, out-of-tolerance dimensions, chipped edges and missing corners that affect assembly and use are judged nonconforming.
3.8 Batch Consistency Control
Party B shall ensure that products of the same batch and model are substantially consistent in appearance, process and performance, with no batch-wide defects, in line with the batch stability requirements of IPC-A-600 Class 2 commercial products.
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