RHOS, CMOS parts and Quality

RHOS (Restriction of Hazardous Substances) was enacted in Europe to reduce six substances in electronics, with lead being one of them.

In the 1940’s there were failures due to something called tin whiskers. These would grow from the tin in the solder and short out the electronics. To solve this problem, lead was added to solder. With the advent of RHOS, I was expecting to see higher failures in electronics. The comments on RHOS around the web vary greatly, however, I would put my trust in a  product representative of a $50K ball grid array solder machine. He said that the RHOS solder is more brittle and has a higher flow temperature.  About the best that you can do for production pass rate is 92% versus 97% for leaded solder. Also, he said that the life expectancy of RHOS assembled boards is about half of leaded boards. If you are doing RHOS, you better have a very good assembly vendor. So RHOS soldering is not recommended for small production houses, or those who prototype for lighting. The nice thing about living in the United States is that RHOS is not required. Also, most of the LED strips and power supplies that I have bought from Ray Wu’s store do not have RHOS stickers. Another interesting note is that the military and NASA do not use RHOS parts in their electronics, the wider temperature ranges require the more flexible leaded solder.

Almost all of the controllers for the smart pixels are CMOS parts. This means that they are very sensitive to static discharge and working on them powered will almost always break a part. Generally, the rule for working with these type of parts is to use a grounding strap while handling and soldering. Most of my failures are due to poor handling of the parts.

Quality is very hard to do well, with the advent of surface mount components, repeat-ability has improved.  With surface mount parts the solder paste and parts can be machine placed, so that you get the same results every time. Also, this reduces the cost of assembly. This is the main reason that most of my boards are surface mount. If there were sufficient demand, the boards can easily be bought fully assembled. However, for those that like to do it yourself, these boards have what are generally considered large parts, and none of the integrated circuits have ground pads requiring a re-flow oven or expensive ball grid array machine.

Since quality is hard, I recommend buying spares. I purchased 200 RGB wired pixels and had one bad pixel. I also have purchased about 1950 strip pixels, and have had two bad pixels. So you can see out of my small sample the strip or machine placed parts have less failures.

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