Before products are put into inventory after final assembly, electronics manufacturing factories always perform quality inspections to ensure product quality. In terms of functional performance, most products go through 100% testing, so pass/fail decisions are usually very clear—unless there are intermittent functional issues. In those cases, it’s still relatively easy to identify good versus bad units. Cosmetic (appearance) judgments, however, are a very different story. Disputes happen all the time. How does your company deal with these situations?

A common scenario is this: the production line supervisor says the product is acceptable, but the PQC inspector says it’s not. The usual reasons are small scratches or slight color differences on the plastic housing. When neither side backs down, quality engineers and process engineers are pulled in to argue their cases. If that still doesn’t resolve the issue, their managers may have to step in and make the final call.

The truth is, cosmetic issues are highly subjective. Everyone has their own opinion, and both sides often feel justified. Workingbear believes the best way to look at cosmetic issues is from the customer’s perspective. If you bought this product yourself, would you even notice these defects? Another key factor is who the end user is—an individual consumer or a commercial user. As long as the product meets customer expectations, that should be good enough.

Individual consumers usually care much more about appearance. Think about buying a new smartphone—you’d probably check carefully for scratches on the case or dead pixels on the screen. Commercial products, such as cash registers or ordering terminals, are usually less sensitive to minor cosmetic defects. That said, different products have different use cases and environments, so the strictness of cosmetic standards can vary. Workingbear still remembers that Japanese customers were the toughest—sometimes even the position of a label on a cardboard box had to be exact, down to the millimeter.

How do we define and control cosmetic standards?

When defining cosmetic standards, the first step is to clearly specify the inspection conditions: lighting, viewing distance, viewing angle, and inspection time.

In our case, we define inspection conditions as follows: under 80–120 lux lighting, hold the sample about 30 cm from the eyes, tilt it within a ±45-degree range in all directions, and inspect for 5 seconds. If a defect is visible under these conditions, it is judged according to the cosmetic standard. If it’s not visible, the product can pass.

Common cosmetic defects include contamination, scratches, burrs, dents, printing defects, color variation, and discoloration. Below are some typical definitions.

Contamination:
We usually define how many spots are allowed within a certain size range. For example, up to three spots smaller than 0.2 mm may be acceptable, while only one spot smaller than 0.3 mm is allowed. In stricter cases, we may also define the minimum distance allowed between two spots.

Scratches:
We first define scratch severity.

• Minor scratches: visible but cannot be felt with a fingernail.

• Moderate scratches: can be felt with a fingernail but not with the fingertip.

• Severe scratches: clearly felt with a fingernail.

Acceptance criteria often differ depending on whether the scratch is on the front, side, or back of the product. Limits are usually defined by maximum width × length, or sometimes by total scratch area.

Color variation (discoloration):
Color differences are usually measured using a color meter, with limits defined by Delta values compared to a standard color sample. Stricter requirements may also specify individual dL, da, and db values.
(See also: Plastic discoloration issues.)

Golden Samples for Non-Quantifiable Items

For cosmetic characteristics that are difficult to quantify—such as the position and size of parting lines, burr size, gate location and size, or sink marks—companies often rely on so-called golden samples.

Today, with modern digital cameras, most cosmetic conditions can be documented with photos and written into specifications. Workingbear strongly recommends using photos for these non-quantifiable standards and including them in the spec whenever possible. This helps reduce reliance on signed golden samples, which are difficult to store and maintain over time.

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