Steve,
Real quick and not necessarily too in-depth at this time, but for COB I consider the following
1 - cost of die/assembly
2 - rework permitted/desired?
A great deal goes in to the board plating and quality. Likely more effort is expended on consistent and quality plating than is required for bonding development.
Assuming no rework (low cost die and boards), one bad wire out of 32 would take you to a 97% yield... but this obviously isn't good enough.
Personally, I tend to be quite conservative - I was originally going to say to you that below 98% you should be jumping up and down screaming. Below 99%, you should be asking a lot of questions. I'm more into the PPM line of thought when it comes to wire bonding, but a great deal hinges on the cost of the product, and the application.... so you can best allocate your resources.
Watch your glob-topping, or dam and fill process (as well as materials) so as to not further decimate your yields.
Steve Creswick
Engineering
Barnett Manufacturing – Evans Machinery Co.
11441 East Lakewood Blvd
Holland, MI 49424
Ph 616 546 8225
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Hackney
Sent: Wednesday, April 15, 2015 7:28 AM
To: [log in to unmask]
Subject: [TN] Wire Bond Process Yield Rates
I would like to get a sense of the process yield rates that should be expected for COB processes. Apologies if this is a duplicate of previous discussions, but I could not find anything directly on this topic.
I understand that process yields are going to be affected by a LOT of variables. Also, I buy into the idea that there is no such thing as “good enough” and that continuous improvement should never stop.
Having said that, I am really just looking for a very rough reference so that I can get a more objective evaluation of my bonding operation performance.
Some rough description of the process and products:
• Pretty good productd volume: ranging from 300k annual to 1500k annual per product.
• One or two die per PCBA.
• Bonds per die fairly low: range between 12 wires and 20 wires per die.
• All die 100% flying probe tested prior to sawing, with 100% visual inspection after sawing.
Our volumes are high enough and product life long enough that we can afford to invest in changes to the product to improve productivity and yield.
My questions are along the lines of these: What sort of yield would make you think to yourself “Yeah, that’s not fantastic, but it’s not too bad either.”? What target would you be trying to shoot for?
Any questions or comments welcome.
Thanks,
Steve Hackney
Toronto, Canada
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