Overcoming the assembly and re-work challenges smaller PCB’s present

Assembling PCB’s with smaller components has it’s own challenges. The rework and inspection challenges are far greater however!

Rework / Repair:

The hero PCB engineer had a tough time designing the PCB as small as was needed. With the best will in the world the electronics engineer made some mistakes which now means that the PCB needs to be reworked or repaired. Now the hero hat goes to the person reworking the PCB.

Back in the nineties and early noughty’s PCB’s were hard enough to repair, cut and hack tracks could be done and legs of IC’s cut and hacked as necessary. Roll forward to today and with track and gaps of 0.15mm or smaller, cut and hacks are much harder. Our poor PCB repair person is desperately trying to find some component pins with not much success.

What can be done?

The key to any chance of success here is equipment. A proper rework viewer like a Mantis isn’t optional, neither is a proper, quality soldering iron and hot air pencil as a minimum. But what about techniques?

Wen it comes to cut and hack’s they’re nearly impossible – but with a sharp scalpel and a steady hand they can still be done. Circuit Medic (http://www.circuitmedic.com/) offers a range of kits which help with the cut and hack process. With everything from tracks in common widths to FR4 delamination repair kits they’re very useful.

Having passives or discrete components inline on the track can help if breaks need to be make – unsoldering them and standing them on end does this perfectly.

Links can be made with some of the small components that are on PCB’s. Where the wire could be butted and soldered onto the joint, today’s small pads break very easily. Instead unsolder the component, solder the wire down and replace the part. This follows for IC’s too – getting that part off is the only way to get to the pad. Make sure that wires are secured down though – any force WILL break them.

The other problem that is obvious with these components with no legs is inspecting them. Using an eye glass just doesn’t cut it – what’s the point of inspecting the soldering of a part like this when the pads are underneath.

CEM’s are increasingly using X-Ray equipment to inspect boards after assembly, but are they using this in the inspection process?

Incredibly not all of them are, using x-ray is an optional extra or has to be asked for especially. While I can understand the business case for such an approach, from an engineering point of view this makes no sense, make sure that it’s understood what’s required of them.

Smaller boards also always mean more layers, more copper and more heat needed to unsolder parts during re-work. I dare to put into print that sometimes the hot air gun that’s needed far exceeds the Jedec specs, but this is the case. Getting all the component to heat up so it can be removed and replaced again is often a necessary evil the re-work hero will have to prepare for. So if there’s someone in the workplace with a hunch , squinting with sore fingers – you found you repair and rework tech. Give them a break and get them better kit!

Circuit Mechanix ©2016


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