Rocky,
I have no standard answer for what magnification to use. A great deal
depends upon the specifications [requirements] you are obligated to meet,
and what your company requires.
I do not completely understand what you wish to 'check on the bonding wire'.
Possibly, you could explain further.
Personally, I do not place a great deal of trust in human visual inspection
for other than the basics. Many of the things which I look for are visible
at low magnification [10-50X]. A great deal of the rest is why I do
statistical process work to keep the process under control.
Many times people become so narrowly focused on a small area [at high
magnification] that they overlook the obvious things [missed bonds, missing
wires, low loops, high loops, etc.] that are readily visible at low
magnification.
Regarding the size of the wire and pad. Without understanding your product,
process and equipment an outsider can not give you a black and white answer.
I suggest that you review the bonding tool manufacture's sites to pick up
additional process information. They generally do a good job of providing
guidelines and making suggestions [however, remember that YOU are the expert
when it comes to your equipment and your product. If it fails in the field,
the blame will fall upon YOU - not them].
Here is the link to Small Precision. I am certain that MicroSwiss/Kulicke &
Soffa is also represented in your area as well as other native suppliers
that I am not aware of.
http://www.smallprecisiontools.com/start-page/?oid=360&lang=en
Wire size - Often it seems as though the IC and bond pads are layed out
first, then the wire size is an afterthought. If possible, use standard
wire sizes. If 75µm square pad, using 31.75µm wire I would go with a
bonding tool having ~50-60µm bond foot if I could.
To make the process as robust as possible, one normally tries to keep the
bond foot as large as possible, yet still fit the bonding pad. The smaller
the bond foot of the tool, the harder the process is to control. Naturally,
the bond must be smaller than the bond pad itself. I am sure that you have
observed that a bond tool with a bond foot of 50µm will create a bond which
is slightly larger than 50µm. You can use this observation in estimating
what bond foot size to use. A great deal depends on the bond pad geometry
and the metallurgy of the bond pad. Frequently, the assembly will be layed
out so that the bond is across the diagonal of the bond pad, creating
additional room on the pad.
Since the IC typically has the smallest bond pads, it typically defines the
bonding tool geometry.
Depending on your product mix and quantity, it may be best to select the
best tool for each application, rather than have one general purpose tool.
An 'average tool' may give you 'average results'. One should try for the
absolute best, if possible.
Possibly there are others with additional comments that may be of
assistance.
Steve Creswick
http://www.linkedin.com/in/stevencreswick
-----Original Message-----
From: Rocky Wang [mailto:[log in to unmask]]
Sent: Monday, November 15, 2010 9:40 AM
To: Steven Creswick
Subject: RE: [TN] Wire bonding inspect method and die bonding wedge choiced
Dear Steve:
Thanks for your comments, I have some concern, need you help, and
in normal COB process, there have several quality control point, as pull
force, shear force test, etc., to ensure the reliability, and there has a
concern, for the visual inspect method, if need to introudce a higher
magnifying glass to check the bonding wire? such as above 100X, how about
the visual inspect method in your section,
More, there should has some math calculation based on the size of
the bonding wire & the pad size, how to handle it?
For the wedge, should have two types, one is can be adjusted for
different PCB, and one wedge which be designed according to the PCB size,
right?
it is very appreciatively for your help, look forward to your
reply, thanks again!
Best Regards
Rocky
________________________________________
From: TechNet [[log in to unmask]] On Behalf Of Steven Creswick
[[log in to unmask]]
Sent: Monday, November 15, 2010 7:31 PM
To: [log in to unmask]
Subject: Re: [TN] Wire bonding inspect method and die bonding wedge choiced
Rocky,
A few simple suggestions.
Visual inspection will provide input on looping consistency & shape, but
statistical methods such as wire pull or shear will provide much greater
insight on bond quality.
I prefer to perform accelerated aging on the wire by baking at elevated
temps to best determine long term reliability.
Most bonding tool supplier catalogs/web sites can provide insight on tool
selection. Use these as suggestions, not absolutes - each situation is
different. Your situation may not be applicable for a 'standard' tool.
Tool life info can also be obtained from supplier. Tool life is greatly
dependant on the application and tool composition. [for example - are you
over-bonding, are your surfaces and wire clean? Are the staff properly
handling the bonding tool during insertion, etc?]. When the process is
statistically 'under control', you can gauge tool wear-out by process
characteristic changes. Many times, the bonding tools are cheap enough that
you should just replace them on a fixed schedule [before they wear out].
Steve Creswick
http://www.linkedin.com/in/stevencreswick
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rocky Wang
Sent: Monday, November 15, 2010 1:25 AM
To: [log in to unmask]
Subject: [TN] Wire bonding inspect method and die bonding wedge choiced
Dear Technet:
After bonding wire, we use the 10x~40x microscope to inspect the wire
bonding quality, how about your section? If need to carry out a higher
magnifying glass to check the bonding wire?
For the die bonding wedge choice,
1. How about choose the die bonding wedge, there should has some math
calculation based on the size of the bonding wire & the pad size.
2. How often do you change the die bonding wedge?
Thanks anyone can share your comments.
Best Regards
Rocky
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