MM or Inches?

 

During my daily duty activities, I have to meet with several kinds of customer, such as customer American-based, Japanese-based, Taiwanese-based, local sub-cons and etc. With these different type backgrounds of customer, there is a confused issue happens frequently. It regards with the differences of unit of measures system is being used.

 

In term of convenience in technical transfer and communication, normally, all of these companies are straight followed with their original country’s customary measures system. And these are regardless with officially standard implemented by local government.

 

The International System of Units (SI) is the modern form of the metric system and is generally a system devised around the convenience of the number ten. This system of measurement is being used widely in most of the countries, both in commerce and in science day-to-day which we could see this system is nearly universally employed.

 

But, there are three principal exceptions Burma (Myanmar), Liberia, and the United States. The International System of Units is officially adopted by the United Kingdom but not with the intention of replacing customary measures entirely.

 

Millimetre (mm), micron (µm), inches (in) and mil (mil) are the common use units of length in Surface Mount Devices field. The millimetre ( mm) and micron (µm) are a unit of length in the metric system, which is the current SI base unit of length. However, an inch (in) and mil (mil) are also the name of a unit of length in a number of different systems, including Imperial units, and United States customary units.

 

          These 4 system units of length, especially for millimetre (mm) and inches (in) are easy be misunderstanding when we describe the component size in short form, such like 1005, 0603, 0402, 0201….. The short form’s name of component size can be exactly the same but it may be two different sizes of component if the system unit of length are differences.

 

For example, the short form 0402 component in millimeter is equals to 01005 the short form’s name of component in inches. However, if component 0402 in inches, it is equal to 1005 component in millimeter.

 

Below is a conversion table for chip component short form’s name:

 

The mistake could be happened if we only look into component short form’s name as reference. For instance, if a customer only informs the component name 0603 who would like to purchase a tape feeder. You may issue a wrong tape feeder to customer if 0603 size is in Inches. This also will be happen in machine nozzle requirement issue. So, in order to avoid any misunderstanding on component short form’s name, I will always confirm with customers about the requirement of component short form’s name provided is in MM or Inches?

 

References : http://en.wikipedia.org/wiki/International_System_of_Units

 

Quoted by : Mr. Foreman, 28 August 2009.