Whenever I need to rework epoxy from a component location, I specify in the process that not all of the old epoxy needs to be removed, just enough to be able to replace the part. There is no sense in scraping down to the solder mask. A small amount of old epoxy residue can be left. Underfilling can still take place after the part has been replaced.
And the most wonderful tool for removing epoxy is the Detail Master Excalibur. http://www.detailmasteronline.com. Our operators love them. Yes, it is a woodburning tool, so what?
They have about a thousand different tips that can be used. http://www.detailmasteronline.com/pen_tips.html. (Ok, maybe not a thousand, but a huge selection).The tips are razor sharp and that combined with the hot tip allows them to slice through even the toughest, hardest epoxies and underfills like they are butter. Detail Master has rounded tips, and these work well because they do not damage the soldermask as easily. We use them for removing Loctite, Zymet, Uralane, coating, etc. You can literally "shave" epoxy away without using any slicing motions, and this greatly reduces the chance of solder mask or substrate damage. And they even pass our ESD testing!
I do not allow solder irons to be used for this function, because eventually they will be used to solder and I don't want burnt epoxy in the solder joints.
We also tried an ultrasonic knife, but that is so dangerous because if you even so much as slightly nick the solder mask with it, it leaves a big hole in the mask. However, they have their place in certain rework operations also.
It's good to be a detail-oriented engineer, so there's your Tip of the Day from the Detail Master, heh, heh. :-)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Wednesday, June 19, 2013 7:15 AM
To: [log in to unmask]
Subject: Re: [TN] Calling all chemists-the dreaded underfill
Bob,
For no-flow, or flux-underfill type underfills I had pretty much concluded that rework after being cured was not practical unless the substrate was LTCC or alumina, and even then, success is not guaranteed. Good operator skills are an asset.
For post-applied capillary style underfills, just make sure you have done ALL the testing you want to/can do before underfilling the components.
Results may vary. Subject to the specific underfill utilized...
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann
Sent: Wednesday, June 19, 2013 7:32 AM
To: [log in to unmask]
Subject: [TN] Calling all chemists-the dreaded underfill
Dear TechNetters:
Most of the epoxy underfills on all of our handheld devices are not practically reworkable, even if you believe the marketing hype on reworkable underfills. The adhesive force of the underfill either damages the pads upon device removal, the mask is damaged during the "scrape off"
process. the chemical antidotes sold by the same underfill vendors either damages nearby parts or is highly caustic to employees.
Has anyone approached this rework challenge differently or could conjure up a unique way to suggest trying?
Thanks!
Bob W
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