| The RoHs directive restricts the use of lead (Pb), | | | | chromium, molybdates etc. These are, however, |
| mercury (Hg), hexavalent chromium (Hex-Cr), | | | | substrate specific; in other words they require a |
| poly-brominated biphenyls (PBB) and polybrominated | | | | particular type of under-coating to be applied for |
| diphenyl ethers (PBDE) to maximum 1000 parts per | | | | proper adhesion and protection, which Hex-Cr does |
| million and cadmium to 100 ppm. The restrictions are | | | | not need. This leads to extra costs, in addition to |
| on a homogeneous material basis, which means that | | | | being less flexible operationally. Similarly, lead-free |
| they apply to any single substance that could | | | | solders based on tin-copper-silver alloys have been |
| (theoretically) be separated mechanically. | | | | developed to replace the traditional tin-copper solder. |
| The restricted substances have traditionally found | | | | However, concerns related to durability and reliability |
| extensive usage in Industrial control switches because | | | | still remain. Lead free solders also require a higher |
| they impart strength, reliability and durability. These | | | | reflow temperature. This often entails expensive |
| are crucial properties as the switches often operate | | | | process changes and retooling. |
| in harsh conditions such as in boilers, etc. They are | | | | Achieving RoHS compliance is, to say the least, an |
| expected to have a long life and operate accurately | | | | arduous task for any company. This is equally true |
| and reliably. These restrictions have therefore been | | | | for the switch industry. The difficulties are essentially |
| challenging to the switch industry. | | | | due to the requirement to meet the maximum |
| While the industry has taken commendable initiatives | | | | allowable limits of the restricted substances on a |
| for RoHS compliance, the efforts have neither been | | | | homogeneous material basis. This requires the entire |
| easy nor entirely successful thus far. This is not to | | | | material flow, starting from raw material and |
| detract from the sincere efforts that have been | | | | component vendors, to the end product stage be |
| attempted. The main problem has been the availability | | | | tracked. Also included in compliance standards are |
| of RoHS compliant components and parts. The | | | | consumables like labels, glue, paint etc which can |
| majority of electronic parts available today contain at | | | | sometimes introduce the undesirable substances into |
| least one of the restricted substances: Pigments | | | | the end product. |
| contain cadmium, mercury is present in infrared | | | | An added complication for many control switch |
| detectors, PBBs and PBDEs in plastics used as flame | | | | manufacturers is that clients include the military and |
| retardants, lead in solder joints and inhibited paints | | | | or aerospace sector. There is no RoHS in aerospace |
| contain Hex-Cr. (chromium is passivated by oxygen, | | | | and products with applications that can be considered |
| forming a thin protective oxide surface layer which | | | | exclusively "aerospace" need not be RoHS compliant. |
| prevents oxidation of the underlying metal. Common | | | | However this poses more problems in maintaining |
| oxidation states are +6 i.e hexavalent chromium and | | | | inventory control of RoHS compliant and |
| +3 (i.e trivalent chromium). | | | | non-compliant products for the switch supplier. |
| A number of products have been developed to | | | | While achieving full RoHS compliance is the ultimate |
| replace the banned substances. However, long term | | | | goal of the industrial control switch manufacturing |
| reliability, an important parameter for the switch | | | | industry, managing the transition is the biggest |
| industry, is yet to be established. Examples of such | | | | current challenge. |
| alternates are Hex-Cr, replacements such as trivalent | | | | |