| | Does sombbody know what DPM rate a good and reliable SMT assembly line (incl. solder paste print, assembly and feflow soldering) has? | | DPM is Defects per million, usually measured on components. We run a process consisting of small to medium batch manufacture typically 250,000 components placed per week up to 10 different circuit board types each day. We use DEK 265 screen printer 2 Siemens Siplace placement machines and a surf systems reflow oven. Our DPM rate (as measured at in circuit test) is typically 40dpm. If you would like to know more, email me directly. | Using DPM (Defects Per Million) as a process indicator at test may not be indicative of how well your processes are running. 40 DPM at test may sound good but if you have an army of inspectors and rework people working on the boards your yields may be ok but all of your profits have been spent. You should consider you�re in process DPM or a cumulation of defects found throughout your process(before rework). As an example if a given number of boards were found to have 100 defects at SMT and another 200 at Wave Solder, then the in process DPM would be calculated with the 300 defects.
Something else to consider... (And this is just my opinion) 1) How a defect is calculated. At the SMT process if you have one 144 pin QFP that is placed off pad then that would be considered one defect (placement). On the other hand if that part has 30 pins with insufficient solder then that would be 30 defects and so on.
2) How to Calculate DPMO (Defects per Million of Opportunity). I use the number of solder joints + The number of components = DPMO Now some people will argue that the component should be counted as several possible defects Placed off pad, Wrong polarity, coplanarity, wrong part and so on. I still consider 1 component as 1 DPMO, but I track what caused the defect for my process improvement.
In Answer to the original question we use under 100 DPM for SMT (for most assemblies). In some cases the DPM will Fluctuate from Assembly to assembly due to poor layout, design, inferior components (I'm finger pointing here, there's no way it could be engineering) and so on.
Well that�s my 2 cents
Mike
reply »