Issue link: https://iconnect007.uberflip.com/i/1259453
70 PCB007 MAGAZINE I JUNE 2020 gets managed. Simply put, one needs to under- stand that processes by themselves (excuse the non-technical term) have hiccups. Even when employing in-tank sensors and controllers to monitor chemistry, it is strongly suggested that wet titrations be employed to verify that chem- ical parameters are in check. While wet analy- sis involving titrations may be time-consum- ing, a skilled operator will get accurate results. More on specific aspects of process control in a future column. In this issue of "Trouble in Your Tank," the focus will be on several anomalies that may have their origins in process steps not normal- ly recognized as the root cause of the issue. Assembly-Related Defects It happens. You receive the dreaded phone call from one of your assembly customers. Some of the boards (very expensive ones!) that your company built failed during assem- bly. There were some vias with poor solder flow-up and a few vias with blowholes in the solder fillet. Obviously, the assembly company is placing the blame squarely on you (Figures 1 and 2). In Figure 2, there are concerns with solder- ability as well. For reference, the final (solder- able finish) on these boards is organic solder- ability preservative (OSP). Note the lack of solder fill or flow-up. OSP was also the finish of choice on the other part numbers that did not fail. In Figure 2, the through-hole component lead wetted well. It would be difficult to assign cause to poor component lead wettability. Fig- ure 3 shows another view of the issue. Some additional background here for the troubleshooter: As part of this story, this group of boards flagged by the assembly company was processed through metallization and elec- troplating on the same day. And all the boards in question were of the same part number. Two other part numbers manufactured for the same assembly company processed without issue. Adding further mystery to the problem was the fact the boards passed electrical test before shipping to the assembler. Working Backward to Get to the Root Cause At first glance, you will see that in Figure 1, the electrolytic copper looks very thin yet continuous. However, the blowhole or outgas is quite evident, leaving a void in the solder fillet. Upon re-examination of the coupons associated with this job, some sections did show the copper plating thickness at 0.5 mils Figure 1: Blowhole or outgassing—major void in solder fillet. (Source: RBP Chemical Technology) Figure 2: Poor solder flow-up and possible blowhole. (Source: Carano, Advanced Troubleshooting Course)