| | | | | We understand that testing for ionic contamination and surface insulation resistance measure different properties. We assemble printed circuit boards for other companies. We will not get combs on 90% of the boards that we assemble. | | | | | We have no customer complaints about board cleanliness. We want to begin a cleanliness process control approach focused on monitoring the cleanliness of boards: | | | | | 1 Provided by fabricators. | | | | | 2 At post aqueous washing in our processing | | | | | I think we should be testing ionic contamination. What are your thoughts? | | | | | Dave | | | | Dave, | | | | Yes. Do the ionic contamination testing. How do you know if your oven is functioning properly. Testing your suppliers raw fabs is pretty labor intensive for not much information. I wouldn't recommend it. If you start seeing solderability problems, check it out. If you are qualifying a new board vendor, check it out. As part of a routine process control, no. That's like testing paste viscosity. It's only needed when there is a problem. That's just my opinion. The tighter you run the ship, the better it runs, the more it costs. Find the find the relationship between cost of prevention and costs incurred by actual defects from this source. That's where your answer will lie. | | | | Regards, | | | | Justin | | | Dave, | | | forget what I just wrote. I just reread it and confused myself. it's been a long week!! Use the ionic contamination test to verify that your cleaner is working properly. I don't think it should be used on every lot of boards. That would just consume too many resources for redundant information. Use it to qualify new vendors and to trouble shoot if need be but primarily as a control for your cleaner. | | | sorry about the confusion, | | | justin | | Dave and Justin, | | Just a few additional thoughts and methods. First, if you want clean fabs, include specifications | | as part of your contract for qualified board suppliers to meet the old MIL-P-28809, IPC-TM-650, or? then | | audit cleanliness on a sample level basis at the specified requirement (2 megohms/cm, as an example). | | Second, ensure your internal DI water capability is operating as specified, meter instead of light preferred | | at about 4 megohms/cm. This ensures your assemblies are ionic contamination free in accordance with specified | | requirements. Then, do sample level testing with an Omega meter or other analytical devices indicated previously. | | Sincerely | | Earl | | Earl: What do you mean by: "meter instead of light preferred?" Dave F Dave, As you know, many DI water systems are installed with a low level light indicating when the water goes below 2 megohms, or whatever. I simply meant I prefer a calibrated meter indicating exactly where the level is with respect to what is acceptable and specified. This allows ionic "tracking" over time - or the tool and method needed to ensure process variability and control. Earl
reply »