Embedded techniques marketing consultant and self-described electronics hobbyist Petteri Aimonen has provide you with a wise strategy to verify whether or not the solder joints of ball-grid array (BGA) packaged components are correctly made — by actually shining a light-weight on the issue.
“BGA (Ball Grid Array) packaging for microchips is getting extra frequent as gadgets turn out to be smaller. It is fairly possible to solder with a primary house reflow setup, however verifying the outcomes is troublesome,” Aimonen explains. “The gold normal can be X-ray imaging, however in need of that you should use optical verification with easy prism instruments.”
It won’t look it, however the plastic from this pack of razor blades could be a helpful diagnostic instrument for BGA soldering. (📷: Petteri Aimonen)
In a BGA-packaged surface-mount half, the underside of the chip is roofed in flat contact factors — usually, however not all the time, organized in a grid throughout your entire decrease floor. Small balls of solder are positioned between the chip and the circuit board to which it’s to be fitted, then your entire meeting is heated to soften the solder and make the connection.
It is one factor to examine the solder joints on the very outer fringe of the half, however fairly one thing else to verify those nearer to the center. Aimonen’s resolution, within the absence of an reasonably priced hobbyist X-ray machine, is to shine a light-weight throughout the chip and search for shadows that may point out a brief — and, the place different elements imply that is not attainable, to create a pair of prisms to behave as a BGA-inspection periscope.
“By chopping and sprucing [a] 45° angle in a clear piece of plastic, whole inside reflection makes it act like a mirror,” Aimonen explains. “The sunshine from a[n] LED will probably be directed below the chip, and any mild that will get by is mirrored upwards in the direction of the viewer.”
Mild from the primary prism passes below the BGA half and is mirrored as much as the viewer by the second. (📷: Petteri Aimonen)
“I made my first prototypes from 2mm thick acrylic,” Aimonen continues. “However then I discovered that many PCBs go away solely about one millimeter of area round BGA chips. I did not have any flat sheets of plastic that skinny, however looking by my cabinets I figured that Gillette shaving blade cartridges are made from skinny clear plastic.”
Utilizing this scrap plastic, Aimonen created the prisms by chopping rectangles then sanding them clean to 1,200 grit earlier than switching to a one-micron sprucing paste and a specialist plastic polish. 11 surface-mount inexperienced LEDs flip one prism into a light-weight supply, and the opposite prism serves to redirect the sunshine after it is handed below the half on take a look at — making the hidden solder joints seen to the bare eye.
Aimonen’s full undertaking write-up is on the market on his weblog, Important Scrap.