Try this test to determine paste problems.

This month we look at solder paste slump during preheating. It is important to know how much, if any, of the paste slumps like butter on a hot day during reflow. If solder paste does slump, it can lead to shorts, solder balls or solder beads, or cause variations in solder joint volume on selected joints.

Variation in joint volume occurs when one joint acquires more solder from an adjacent joint during reflow due to the paste being linked. Testing of solder paste is well covered in IPC specifications, and equipment is available to test paste and record the results.

Alternatively, if you think you have an issue, a simple shop floor test is to use the existing profile but change the temperatures of the final reflow zones. Setting the final zones to final preheat temperatures will slow the degree of slump. Normally the maximum slump is seen earlier during reflow. Typically, as solder paste is changed or the metal particle size is reduced, slumping can be seen more often.

Is the reflow profile the problem? X-ray can help.

Looking through some recent x-ray images of what I would call “good bad” boards (at least, that is what they are for me, as they showcase “good” examples of how certain “bad” types of failure look under x-ray inspection), I came across a number of different issues that are different from “traditional” BGA/QFN problems mentioned in this space before. To wit, I noted some images showed where solder paste had not reflowed under the devices, and there was the presence of foreign object(s), such as discrete components, trapped under the package.

FIGURES 1 and 2 show how unreflowed solder paste typically looks under QFN joints in an x-ray image. In the magnified view (Figure 2), individual grains of the solder paste are seen clearly, instead of appearing as a typical single smooth continuous joint. The cause of this is probably not an insufficient reflow profile. Rather, it is more likely the board has not been reflowed at all. As it may be desired, or necessary, to x-ray inspect (representative) boards after placement but before reflow as part of a quality control process, it is worth noting this characteristic shape of the solder under the components is different from what would be expected post-reflow.

What do you do when the excrement starts flying?

I write this in California on Monday, Mar. 18, 2019. Eight days earlier, a Boeing 737 MAX 8, operating as Ethiopian Airlines Flight 302, crashed six minutes after takeoff in clear air on what should have been a routine flight from Addis Ababa to Nairobi. The equivalent route flown in Africa as a flight from San Francisco to Los Angeles. A milk run, as pilots say. Some 157 innocent souls didn’t make it.

This follows a crash five months earlier in Indonesia, under similar circumstances with no apparent weather-related impediments, of the exact same aircraft type shortly after takeoff, with similar loss of life.

It is irresponsibly premature to draw sweeping conclusions from this most recent crash, as the investigation into both disasters continues. Much remains to be learned, and early theories of causation could be proven wrong. Eerie similarities between the two incidents have emerged from the evidence reviewed thus far, however, and we already know a few things. Those few things prompt anxious questions now.

Cutting time-to-market and shipping errors using Lean principles.

OEMs “new to outsourcing” represent a special challenge for electronics manufacturing services providers because often their systems and processes are not as defined and documented as those of companies that regularly work with EMS partners. Nevertheless, such OEMs also represent the segment of EMS customers able to leverage the most value from a successful outsourcing partnership, provided the EMS company properly sets expectations. Lean manufacturing philosophy’s focus on process improvement and elimination of non-valued-added activity provides an excellent roadmap in this expectation-setting process.

The seven wastes provide ample guidelines for areas of improvement in transitioning new-to-outsourcing projects: