Reliability Analysis for board

MIL-HDBK-217F provides some information. For tools, one choice to look at is Item Software. You enter all your parts and out pops a failure rate for the whole thing.

Time to get some books on probability and statistics, or go back to school. You do not have the background for that job. BTW, your shift key is broken, as is the apostrophe, which makes your article hard to read.

Calculating reliabilty can be a complex and difficult procedure. Strictly speaking you need to know the operating environment of every component, its electrical stress, its reliablity and and manufactured quality. Some software has been written to do this but is is expensive and its value and the accuracy of its results is questionable.

To get an idea of the likely reliability at the design stage, the parts count method can be used. This assumes common environment and stress levels on all components and uses a simple multiplying factor for different qualities of components. For each type of component you work out the failure rate from the base falure rate for that component multiplied by the environment multiplied by the quality factor multiplied by the number of components. Then sum these valuse for all components to get the overall failure rate. take the inverse to get the mean time between failures.

I first came across the parts count method in the old US MIL STD Reliabilty Handbook which may still be available. The only problem with this is its values tend to be rather pessimistic especially with the advances in component quality caused by the consumer electronics explosion. At that time I created a spreadsheet which saved a huge amount of effort in calculating reliability. You just entered the number of each type of component and out popped nine answers covering each of three different environments and three different quality levels. Some years later I created a DOS version of this which I released as shareware. I got just one registration. I still have it lying around somewhere and you are welcome to a copy if you widh.

Ian

hi Ian,

first of thank you all for your kind replies. i really got some good info. now what i want to know is to calculate failure rate for individual part from where i can get this quality factor (PiQ) and enviornment factor (PiE).

also how can i calculate base failure rate? is there any formula for this.? is same i.e. "Lamda G"?

if i m right with this information, then i just have to calculate part failure rate = quantity x base failure rate x PiQ x PiE

I m waiting for reply.

thanking you, shridhar.

hi

i just gone through MIL-HDBK-217F document n found useful information. What i think now that for base failure rate (lambda B) and all other factors like enviornmental factor (Pi E) , quality factor (Pi Q), Application factor (Pi A) etc.. i can look in to this document.

just find out the suitable vaules depending on ur operating enviornment( ground benign, ground fixed or airborne applicaiton etc), quality designator(screen level) and also with ur junction temperature from this document (MIL-HDBK-217F) and them calculate part failure rate, which then multiplied with the no. of components (quantity) .

am i correct with this assumption.? waiting for ur reply.

thanking you, shridhar.

That is correct. These are the values I used in my program.

That is basicaly it. However, you should be aware that the MIL STD Handbook takes a rather pessimistic view of the quality of commercial (that is non MIL SPEC) components. IIRC PiQ is about 35 for commercial grade components which IMHO is far to high.

Ian