The IPC does an excellent job of establishing acceptability standards for PCBs and assemblies. We have sent several employees to the training and then used those technicians to train others inside our operation. A really important part of the PCB industry infrastructure…especially for the lawyers.
Let’s dig deeper than the differences between Terrible (Class1) , Okay (Class2), and Really What You Want (Class 3). What about the marginally acceptable Class 2? What about Class 2 that is so good it almost or actually qualify as Class 3? Let’s keep the lawyers out of this and talk practicality.
Case in point. A shipment of PCBs come in and go to inspection. The drill hits are NOT perfectly centered but do not break out of the ring. QA determines these acceptable by Class 2 criteria. What are the sub-criteria you should apply to possibly over-ride them? (Now your nose is in this.)
- Has this happened before with this supplier? If yes, then shame on you. First time the dog bites you, it is the dogs fault….
- Is this a complex board? If not, then possibly the marginal product will not affect anything and, by the way, production is hurting for the boards. So you accept.
- If yes, it is complex, then consider this. On complex printed circuit boards, marginally okay problems are often indicators of other deeper issues. Fundamentally, it means the pcb manufacturer’s processes are slightly out of control and are possibly out of control in areas you cannot see on incoming or are not picked up in bare board testing; a glacier if you will….and maybe a time bomb. (Sorry for the dual metaphor, but it seemed to work.)
- What is the expected life of the board in use? Consumer products are often tossed after 6 months use. Industrial products often stay in place for 20 years. What are your standards for useful life. Deeper problems normally surface after some field use and exposure to temperature changes or getting bounced around.
Our approach is using IPC standards as a starting guide, a base if you will. We then overlay time tested principles of Continuous Improvement and Passion for Excellence. We don’t like any marginal boards.
So, how do you put your nose in and not get punched?
- Train your pcb suppliers instantly that marginal product will not be accepted.
- Send them your own criteria as a business for how close to perfect you expect (this is the “What We Really Want Class)
- Some great suppliers are not great at everything you need. Sort your suppliers by skill complexity.
- Be realistic about what is actually important and will affect your customers and your company.
I am not suggesting you tangle with QA. I am suggesting that fixed standards do not apply to all business decisions. Your QA folks and your company will benefit from setting your own acceptability standards.