On 23 December, D. Rooke wrote:

> How do you 'waste' components during placement?

after Larry Morse asked:

>>     I am attempting to arrive at a reasonable figure for the amount of 
>> components that should be provided for SMT assembly, over and above the 
>> actual component count needed to complete the boards (i.e. to compensate for 
>> components wasted during placement). 1%, 3%, 5%, or whatever.   If you know 
>> of an industry standard, or have a company policy, I'd like to know what it 
>> is.  My email address is "[log in to unmask]".  Thanks.

Larry,

     Maybe the word "waste" was misunderstood by D. Rooke. Having worked in 
contract manufacturing companies over the past 9-years, and having to deal with 
the consigned material that is supplied with the products that we've built for 
customers, I know EXACTLY what you're asking. A good figure that seems to kinda'
"palatable" to customers that understand the situation, is 3% for passives, and 
1% for actives.

     Now to why it's important to figure a little extra in for that "waste"... 
It's not really wasted components, but it's the amount of components that will 
_NORMALLY_ "fall-out" during the assembly process. If it was a perfect world, 
every single little component that's been bought for a product will be used in 
assembling that product, and not be "wasted"...  

     But in reality, you're going to have some attrition. You even shouldn't be 
too shocked to lose a whole assembly once in a while in the process...somebody 
drop's a board and breaks off a corner, or you have a "submarine-job" at the 
wave soldering machine...hey after all, feces happens once in a while. 

     One of the things that I've seen a lot (especially with consigned SMT 
material), is to be given the exact numbers of components for the exact numbers 
of assemblies to be built. Ya' know, you've got a kit of 1,000 fabs, and ya' got
a resistor that goes 1-per, then ya' get a strip of 1,000 resistors in a little 
plastic bag, not on a reel even, and no top film leader either! HA! What a joke!
I've even gotten some of those 1,000 resistors in ten 100-piece strips before 
from some of the "sharper" stockrooms I've worked with in the past...it goes to 
show ya' how out of touch some materials people are with what actually goes on 
out on the production floor... 

     There's components that's going to be discovered failed at test after 
assembly that'll need to be replaced, and the pick and place machine is going to
find a few visually bad components once in a while, or it'll just mis-pick some 
now and again, then reject them. Those components all wind-up in the machine's 
reject bin, and they may be fine functionally, but let's say for instance in the
case of chip resistors and capacitors, are ya' gonna' send them back out to get 
em' tape and reeled so ya' make sure you use them? You'll probably wind-up 
paying 10 times what the component actually costs to get them tape and reeled. 
Another thing that happens at the pick and place machine is that the top film on
a reel of components will break for whatever reason, peel-force is too much, or 
an operator just happens to break it when he's changing another feeder, you can 
easily lose 20-30 components just peeling back enough top film to thread the 
feeder...and I don't even wanna' talk about 0603's or 0402's!!! You sneeze and 
there goes a couple hundred of them little puppies!!

     Don't get me wrong, I really am a "frugal" kind of guy and don't ever like 
to waste anything, but when you set-up a job to be built using automation, it 
really does wind-up costing many more times the amount of money that someone 
thinks they are saving by not supplying any attrition!


   (DO YA' HEAR THAT THOSE OF YOU THAT USE CONTRACT ASSEMBLY COMPANIES TO BUILD 
   YER' SURFACE MOUNT? ESPECIALLY THOSE OF YOU THAT SUPPLY US WITH CONSIGNED    
   MATERIALS?)     
                  
                                                          __\/__
                                                      .  / ^  _ \  .
                                                      |\| (o)(o) |/|
                                            #------.OOOo----oo----oOOO.-----#
                                            #          Steve Gregory        #
                                            #      SMT Process Engineer     #
                                            #  The SMT Centre Incorporated  #
                                            #   [log in to unmask]   #
                                            #________________Oooo.__________#
                                                      .oooO  (   )
                                                      (   )   ) /
                                                       \ (   (_/
                                                        \_)
   

  

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