I am intrigued by the theme of this month’s issue—“What You Need to Know”—because it is such a broad subject. There are lots of things we need to know. So, like most of you, I could hardly wait to read this issue of SMT007 Magazine myself. While others focus on addressing various aspects of this expansive topic, I will address some key issues that I think are important for us all to be aware of and learn about. And before I proceed, I am going to make some assumptions about my readers to narrow the focus of this column. The subjects are not technical but managerial, and the target audience is managers in the SMT assembly industry and engineers who aspire to be future managers.
Why is it important? Most companies attempt to achieve higher yield in SMT products through trial and error at considerable expense and frustration. Even though we have been manufacturing SMT products in high volume for almost three decades now, less than 10% of companies have first-pass yield (FPY) of more than 90%. In other words, 90% of companies are conducting too much rework. Rework adds to the cost of the product and reduces the reliability of solder joints due to an increase in intermetallic thickness each time the solder joint is reflowed. So, what are the reasons for this high defect rate?
• The processes are at very high speeds, and machines must perform them
• The equipment must be characterized thoroughly; this can be defined as understanding all parameters that affect the equipment’s performance, and vendors may say it is easy, but it is not
• Most large companies have assigned engineers to optimize, and most small companies learn as they go, but learning as you go is not an option because revenue or product schedules (or both) may be impacted adversely
With the advent of fine- and ultra-fine-pitch, high-pin-count BGAs—0402, 0201, and 01005 resistors and capacitors—as well as the widespread use of no-clean flux, yield problems are getting worse, especially when you use large BGAs and BTCs in addition to a smattering of through-hole components on the same board in a lead-free process.
To read this entire column, which appeared in the December 2019 issue of SMT007 Magazine, click here.