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April 2011

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From:
Steven Creswick <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steven Creswick <[log in to unmask]>
Date:
Thu, 28 Apr 2011 13:42:08 -0400
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Victor,

 

I can not dispute that 883 is quite vague when it comes to detailed specifics.  It was, after-all, only intended to list test methods and min or max limits.

 

In the three semiconductor packaging companies I have worked at, and all that I have visited over the years, each has had its own detailed documents dealing with the items you are seeking.    It appeared that all were level-headed reliability/engineering interpretations of the Mil Std and projected application.   Each company treats this information as reasonably proprietary.

 

With respect to the items you bring up below – it all depends on the application.

 

Many will require adhesive fillet ¼ - ½ way up the side of the chip, but doing this on an LED with a bottom-side junction will short it out.  Generally, the farther up the adhesive goes, the more it spreads out.  Most high-density applications value that lateral space.  True, fillets increase strength during die shear, and can significantly help with heat dissipation, but those are product specific items that you can tweak your documentation for.  Generically, if you can see adhesive, you have a fillet in my book.  If you have the real estate for large fillets, well go ahead [within reason], but you had better not get it ANYWHERE near my wire bond pads!  J

 

WRT to bond-line thickness, I have found that generically one gets about 12-18µm without trying much.  That is not something I measure all the time, and only do so by cross-section.  This is reasonably applicable to LEDs and mm size die.  When you go to larger die [say 4-5 mm per side and up], you sometimes have to take into account thermal dissipation and CTE differences between the device and the substrate.  Sometimes you go with a lower modulus adhesive and keep the bond-line thin.  Sometimes, you go with a thicker bond-line [usually by adding spacers such as glass or metallic beads] …. It all depends [trademarked by Dewey]

 

Die placement angle is dependent on design requirements and the amount of skew the wire bonders can accept without getting into a tizzy.  I have had die placed as much as 10-15 degree askew and the wire bonder will find them and bond them.  Generally not a good idea because wires tend to be crossing and looping goes wacko, but is ultimately a function of design and layout – and common sense. 

 

With respect to corner coverage … well, it all depends again.  Myself, being on the conservative side, I don’t feel that anything less than 100 bond-line coverage is acceptable.  Typically, die bonders can easily get 100% coverage with small fillets on the full perimeter, so why should I accept less? – with certain caveats.  If the device requires no electrical back-side contact, and it is a jelly-bean commodity type of part, and is proven to be stable enough for reliable and repeatable wire bonding, 75% coverage could/should be acceptable, but it all depends on material and application.

 

Boiling it down in a nutshell, when at the beginning of the packaging process [such as die attach and wire bonding are], I prefer to do things which maximize my reliability, so I push for 100% bond-line coverage [subject to device type], and maximize my wire pull values [both initial and as a result of accelerated aging testing] – regardless of application.  From my experience, it really does not cost any more to do it ‘right’, but it sure costs a whole lot more when you cut corners and it comes around to bite you in the rear later…

 

My long two bits

 

 

Steve Creswick

 <http://www.linkedin.com/in/stevencreswick> http://www.linkedin.com/in/stevencreswick

 

 

 

 

 

From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Thursday, April 28, 2011 12:47 PM
To: [log in to unmask]; [log in to unmask]
Cc: [log in to unmask]
Subject: RE: [TN] Die bonding requirements

 

Steve,

 

   I was vaguely award of these TM but when I went to visit the MIL-STD-488A-B document the light went on again.   However, this is not what I was searching for.   The other Big Blue, previous life, had an internal document which was more user friendly with text and more photos of what was permissible and what was a non compliance anomaly.

 

Victor, “X”

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Thursday, April 28, 2011 10:13 AM
To: [log in to unmask]
Subject: Re: [TN] Die bonding requirements

 

Victor,

 

You could start with the old Mil-Std 883 and the following test methods.  IPC likely has equivalents as well, but I don't remember them as readily.

 

TM 2010 - Internal visual monolithic      Page 41,  2010.3 Detail A (Side View) & Detail A (Front View) does give very much criteria on bonding material examination.   Min thickness of bonding material, permissible angle, if skewed, voiding, side coverage (height of die thickness) and four corner edge coverage.

 

 

TM 2017 - Internal visual hybrid          Page 12,   2017.1  same as above.

TM 2019 - Die Shear

 

However, first, with a firm of your size, I would look internally.  I'm sure you have all the information you need there - somewhere...

 

Relative to visual criteria for die attachment and dicing - Most of us in the hybrid industry took the Mil Std as the ABSOLUTE MINIMUM requirement.  If we were to ever approach the limitations of the Mil Std, it generically meant that something was royally messed up and one should be VERY concerned.  

 

Visual criteria can also be significantly different within the same facility for Mil, Space, Implantable medical, Automotive, Commercial, etc., so you need to know what product type you are seeking to glean info on/for.

 

 

Steve Creswick

http://www.linkedin.com/in/stevencreswick

 

 

 

 

 

-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez

Sent: Thursday, April 28, 2011 9:28 AM

To: [log in to unmask]

Subject: [TN] Die bonding requirements

 

Fellow TechNetters:

 

   Where can I find die bonding requirement.   I am not familiar if IPC address these issues/concerns.   The same goes for die cutting anomalies.

 

"X"

 

 

 

 

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