Component marking: is it really required?

ESUK Jul13 p28_30 Anglia2Anglia Components‘ marketing director, Graham Bridger, asks whether components still need to be marked in an era of automated electronics assembly

These days, most electronics sub-assemblies are manufactured automatically, so do components still need to be marked? Chip capacitors have, after all, not been marked for some time, and the smallest chip resistors, of 0402 and below, are normally unmarked too.

Much discussion has been provoked by the decision of Yageo to withdraw markings from 0603/0805/1206 size chip resistors with effect from July 2013. While Yageo cites environmental reasons, such as the use of ink, some customers feel that the change is really driven by cost considerations. Providing the correct reel is loaded onto the pick and place machine, then the correct component will be placed on the board, however, other chip resistor manufacturers like Eurohm have confirmed that they will to continue to mark their chip resistors and have no plans to make this change.

Markings explained

Traditionally, manufacturers like Eurohm have marked 0603, 0805 and 1206 chip resistor devices with a three or four digit code to designate the nominal resistance value. This enables users to confirm which device has been placed on the board.

With three digit marking, for values up to 91 ohm the R is used as a decimal point. For values of 100 ohm or greater, the first two digits are significant, the third is the multiplier indicating the number of zeros to follow.

With four digit marking, for values up to 988 ohm the R is used as a decimal point. For values of 1k ohm or greater the first three digits are significant, the fourth is the multiplier. Zero-ohm resistors are marked with one or more zeros.

Three digit codes are used on all five per cent tolerance resistors in 0603, 0805 and 1206 sizes and four digit codes are used for one per cent tolerance chips, except for 0603 resistors where the size limitation prevents the use of four digits. Here a three digit code is used with an underline under the multiplier to denote one per cent tolerance.

Inspection benefits

In taking the decision to remove markings, Yageo has ignored some specific issues regarding the way that mid-size chip resistors are used. The 0603 to 1206 range is the preferred size for industrial electronic manufacturing in the UK today since these applications generally don’t demand the space savings associated with the very smallest sizes.

The problem is that, whereas a board will typically have no more than one or two different values of chip capacitor on it, it might have many different chip resistors, which could easily be muddled by misplacing a reel. That’s why customers use automatic optical inspection (AOI) to verify their boards, including inspecting component markings. In this way, a reel loading error will be identified much more quickly than if verification is left to an end of line functional test.

In the end, the customer should come first. If customers require components to be marked, this should absolutely be continued wherever practicable. After all, any cost and environmental benefit achieved by removing markings will be completely lost if even a few hundred additional boards are assembled incorrectly.