Defect of the Month – Popcorning

Hello, my name’s Bob Willis and welcome to Defect of the Month. Every month, I try and provide an example of a particular defect and hopefully some solutions. I’ve made over a hundred different defect videos over the years so hopefully one will solve one of your production problems.

 

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Now popcorning on surface mount components has been around for many years. I remember seeing it very, very early on in my career at GEC when we introduced a SMT with some small parts. If the moisture increases inside plastic components it can expand as a gas and try to escape. So quite often, you’ll see a crack in the package around the edge of the plastic moulding to PCB interface on Plastic Ball Grid Arrays (PBGA)

If you’re using some BGA packages the crack will occur in the top of a plastic package or on the bottom of a plastic and in any one of those situations, potentially it can cause you an intermittent or a complete failure of the part. If you’re doing rework and repair of a package on a board it’s good practice, particularly on high price boards with more expensive parts to bake out the board assembly before you remove any components. This is also true if you’re going to do failure analysis on that particular part. If you’re just going to take it off and throw it away, it’s perhaps less important. You also have to remember about adjacent components because they too could actually see much higher temperatures during rework and repair

If you’re a rework engineer or an operator you may have heard parts crack or pop, I’ve certainly experienced it and you may well do to. If a package does pop, you can actually hear it when you are concentrating and watching for reflow. That’s why this defect was referred to as popcorn or popcorning in the early days you can generally see the cracks top and bottom of a plastic part. And just at the interface on the plastic moulding on BGAs in worse case situations, you might see it on the top of the plastic. It can be due, as I said to the moisture, but also to excessively high temperatures. So if you are reworking or reflowing at higher than normal temperatures, the package can be more susceptible to cracking. It is possible to do failure analysis on these parts using SAM Scanning Electron Microscopy

This  technique is non destructive, you can look inside and see where cracking and separation may have occurred without destroying the part. You can do micro sections, x-rays and other methods I show on my Failure Analysis Workshops. If you want to find out more about moisture sensitivity the defects that occur in manufacture because of poor control or poor monitoring or poor use of parts, then you can refer to the IPC JEDEC 033

Thank you very much for listening to defect of the month. Hopefully it’s been useful and possibly you’ve found a solution to one of your process problems. So just a reminder that if you want to listen to more defect of the month, subscribe to our channel, if you just like this individual video, then please like it. And of course share it with some of your colleagues in manufacture and in other companies, it all helps to bring information to both production and engineering staff. If this short introduction to this particular problem was of interest to you, then of course we can hopefully provide you a solution to aid. You eliminate more process defects within the future. Finally, if you’ve got a defect and you’d like it covered in a future Defect of the Month, then let us know. Thank you very much.

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