AQL Basics: Acceptance Limits for LCD Orders

AQL is not a defect rate target for the whole lot; it is an acceptance limit for sampling. A statement like “major defects AQL 1.0” means the sampling plan is designed so that lots whose true major-defect level is at or below 1.0% are accepted with high probability. It does not mean the supplier is allowed to ship 1% defective units as a goal—it is the boundary the buyer and seller agree to enforce through sampling.

Three elements define an AQL agreement:

• The sampling plan — lot size, sample size, and acceptance numbers.
• The defect classes — critical, major, and minor, with their limits.
• The inspection conditions — lighting, viewing distance, and which checks count as defects.

AQL Sampling Tables: ISO 2859-1 Explained

Most LCD orders use sampling tables based on ISO 2859-1 (the international version of the classic ANSI/ASQ Z1.4 approach). The table works like this:

1. Determine the lot size — the number of units in the shipment or batch.
2. Choose the inspection level — general level II is common; tighter levels increase sample size.
3. Look up the sample size code letter — from the lot size and inspection level.
4. Read the sample size and acceptance numbers — from the AQL column for each defect class (for example, Ac/Re of 5/6 at AQL 1.0 for a given sample size means accept with up to 5 defects, reject at 6).

The plan is a pair of numbers: how many units to inspect and how many defects trigger rejection. AQL values such as 0.65, 1.0, or 2.5 are commonly seen in display orders; the right value depends on the application (automotive and medical usually demand tighter limits than consumer). Examples from suppliers are just that—examples—so set the value from your product’s needs and write it into the PO.

Defect Classification: Critical, Major, and Minor

Defects must be classified before inspection, because each class has its own AQL:

• Critical — safety or regulatory defects; typically the limit is zero (or an extremely tight AQL).
• Major — defects that affect function or visible quality within the acceptance area, such as dead pixels, mura, or scratches in the active area.
• Minor — cosmetic or edge defects outside the critical viewing area that do not affect function.

The defect definitions belong in the inspection specification, not in the buyer’s head. Two suppliers can inspect the same panel and reach different conclusions if the definitions of “dead pixel” and the viewing conditions differ.

Inspection Points: Cosmetic, Optical, and Electrical

An LCD inspection covers more than pixels:

Each area needs defined conditions: lighting level, viewing distance, and power-on warm-up. Inspection performed in different conditions produces different defect counts, so the conditions belong in the agreed specification.

Common Inspection Disputes and How to Avoid Them

Most AQL disputes are not about the tables; they are about definitions. The usual disagreements:

• Defect definitions — what counts as a dead pixel or scratch, and where it may appear.
• Inspection conditions — lighting, distance, and whether the panel is powered or backlit.
• Sample handling — who selects the samples and what happens to units that fail.
• Boundary lots — results that sit exactly at the acceptance number need a pre-agreed decision rule.

Prevent disputes by attaching the inspection specification (definitions, conditions, and plan) to the purchase order. If the spec is a separate document, reference its version number in the PO so there is no ambiguity about which one applies.

Inspection Reports: COA, Photos, and Rework Decisions

The inspection outcome should be recorded, not remembered. A complete report includes:

• The plan used — lot size, sample size, AQL values, and acceptance numbers.
• The results — defects found per class, with photos of representative failures.
• The decision — accept, reject, or conditional, with the reason.
• Rework or sorting plan — if a lot is rejected, what happens next: 100% sort, rework, or return.

Certificates of analysis (COA) and photos give both sides a common record when the next lot arrives or a field issue appears.

Setting AQL in Your Purchase Order: Agree Before the PO

Write the AQL agreement into the purchase order before production, including:

1. The inspection standard (for example, ISO 2859-1, general inspection level II).
2. The AQL values per defect class (critical, major, minor) for your application.
3. The defect definitions and inspection conditions document (with version).
4. The location of inspection (supplier, buyer, or third party) and who pays.
5. The decision rules for rejection, sorting, and rework.

AQL figures such as 0.65 or 1.0 appear as common examples in supplier materials; they are external examples, not a CDTech commitment. Set values from your product requirements and confirm the supplier’s service terms in the agreement.

Frequently Asked Questions