Dave,
I have never seen a "definitive" MIL, IPC or similar, spec for a
clean board suitable for wire bonding, most manufacturers often just in
house test and supply stuff to their specific customer requirements and
specifications. I have some old specs from previous jobs, but they are at
home, so I cant get them unti later, if you are interesetd, let me know. In
the mean time, if anybody else has got one Id be interested in a look see.
One question relating to the analysis for contamination, how was it
done? Even with heavy wire, (U never mentioned the wire size) a very thin
contamination layer can give bond problems, and depending on the analysis
technique you may not even see it. EDX for example tends to "punch" through
anything "thin" cant remember the numbers off the top of my head but you
generally pick up the substrate material and not the contaminant. I would
suggest Auger, or XPS to look for stuff, but expect to see a lot of C and O,
but look at their relative thicknesses, a heavy layer of C acts like a
lurvely greasy film and the bond tool slips like a skaters boot on ice.
Have you considered a micro hardness test, could be the plating is
embrittled with H, this would give an intermittent bond, but those that do
stick would have a low strength. you can test for this by baking to see if
you get bubbles in the plating. Another thing to look at is the shape of
the bond foot under the joint, assuming you can get a bond that sticks,
dissolve the wire off Sodium Hydroxide (10%) and take a look at the foot
impression on the pad, you can measure the contact area, and note where if
the bond debris lies. Also, on miss bonds, is there any pad material on the
bottom of the wire foot, could be there is delamination or something up on
the plating, with the plating be the weak point in the system.
Dont know what else to say, but if you have panels, and need to get
em to bond, all the "bondage, sorry bonder people" will need as much info as
possible.
Good luck,
Roger
-----Original Message-----
From: Dave Gardiner [mailto:[log in to unmask]]
Sent: Wednesday, September 27, 2000 2:47 AM
To: [log in to unmask]
Subject: [TN] ENIG SMD PWBs Aluminum wire bonding
Thanks all for your suggestions on epoxy bleed. Plasma clean and vacuum
bake are being investigated. Has anyone seen any specifications that
cover epoxy bleed or bondability. We have one part number where we have
twice had trouble with no stick to 15 grams pull on the same panels. We
had tests done for surface contamination but there was little difference
in the findings between good and bad boards.
Dave Gardiner
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