Wire Bonders' Speak

Improving Wire Bond Strength and Reliability

Since the early days of wire bonding, engineers have been looking for ways improve the strength of the wire bond interconnect and improve its reliability. This is espcially important for industries with high realibility requirements: aerospace and defense, implantable medical device manufacturers, automotive, commercial optolectronics and telecommunications (RF/Wireless). For example, a heart pacemaker can't go "bad", a weapons system must hit its intended target...more industries with strict wire bond requirements are popping up all the time. Which brings us back to the point: making strong wire bonds can be the difference between success or failure, profits or loss, and even life or death. This may seem dramatic, but it is not - this is the reality of packaging microelectronics in high reliability environments.

The Security Bump and Stand-off-Stitch

The Security Wire was, for many years, the only way to achieve a stong wire bond. Now with the demand for smaller package size plus even further bond strength, new methods have been discovered. One such method is the Security Bump - it requires a smaller second bond termination site. 

Stand-Off-Stitch (SOS), which is Stitch on Bump, and defined as 1) placement of a ball bump at one end of the wire interconnect, 2) then placing a wire with another ball at the other end of the interconnect, and 3) stitching off the wire on the previous placed ball bump. SOS has many benefits that can be incorporated into a variety of applications such as circuit design. Here one can accomplish, with Stand-off-Stitch, better wire strength, fewer interconnects (die to die bonding) and lower loops. Reverse bonding is another use of SOS (reversed bonding defined as stitch bond on bump on die bond pad). This often results in a lower loop profile than standard forward wire loop. Also, the loop is much stronger because the wire hasn't been annealed above the ball, in the Heat Affected Zone.

Why the need for Auxiliary Wires?

This paper was inspired by the many customers Palomar has served over the years and the common problems/challenges faced when presented with wire bond application needs. Using Palomar's Versatile 8000 Wire Bonder/Ball (Stud) Bumper, these methods discussed have been developed, tested and proved. Some of these problems/challenges include poorly bondable materials, non-flat bonding surfaces, odd or uncommon packaging situations or just the need for higher reliability.

Motivation for Improving Wire Bonds

1. Increase Pull Strength of Stitch Bond
2. Improve Failure Mode from Destructive Pull Tests (more Mid-Span and Neck breaks than Tail Breaks even with Poor Materials)
3. Improve Bond Strength after High Temp Burn In 

Auxiliary Wires, Security Bumps and Stand-off-Stitch were developed to overcome these challenges and provide customers with rock solid packages that can withstand even the harshest environments. 

See in Action

Contact us with any questions on High Reliability Wire Bonding. If you are interested seeing Mr. Rasmussen's entire presentation on this topic, register to attend SEMICON West in associated with IMAPS Workshops "Wire Bonding Workshop", held at the San Francisco Marriot on July 14-15. 

This is the second blog in my "Guide to Buying a Wire and Die Bonder". It is vital to KNOW YOUR OPTIONS. Knowing your options will better help you maximize your return on investment over the long run by choosing the best bonder to meet your application needs. 

The New Bonder: much like a new car, the new bonder includes a full factory warranty and has been driven only a few gentle miles during acceptance testing. It has the new car smell, you will park it up front where everyone can see it - you especially can show it off to customers and senior staff. You will feel like a King (or Queen) - the entire capital equipment manufacturing team, of from whom you bought the bonder, is at your disposal - for it is their primary objective to satisfy you!

Although bonder manufacturers do their best to make lead times as short as possible, lead times for new machines can be longer if a) there is signifcant process development, and b) if customized material handling or tooling is required (and this can be said for all the choices)

The Demo Bonder: demostration or "demo" equipment is used at the manufacturer's site to demostrate capability and perform application for customers who are interesting purchasing equipment for their own facility. Demo systems can be a good option for customers looking for "new" equipment at a slightly reduced price; the demo system also benefits from having been "hardened" at the factory under the close supervision of the technical staff who built them. Although demo bonders have not changed title, they have seen a few application miles and been trotted around on the dog and pony show more than once. Typically, bonder manufacturing firms rotate demo machines in order to keep them fresh, and in doing so will usually only sell a few a year. Manufacturers don't rush to sell demo systems as they must backfill that demo system with a shiny new one. Because of this, demo equipment's discounts are usually modest. With this said, if you are interested in a demo system, it is best to contact the bonder manufacturer as early as possible - like anything, it is first come, first serve. Depending on your applicaiton, a demo system may require you to be flexible in your timing, accesories, tooling and material handling. These additional items are sold at "new" prices, as they were not originally part of the demo bonder.   

The Refurbished Bonder: a good microelectronics packaging system manufacturer will offer refurbished systems to its customers. A refurbished wire or die bonder is a good option for those seeking performance at a bargain price. Generally speaking, refurbished systems come from buy-backs from good customers - good meaning these customers have taken great care of the machine and kept it in good working condition. Also, these machines are almost always covered by the manufacturers service contract and warranty. Refurbished means to return the system to its near-original-condition. If neccesary, it is cosmetically repaired. The computer systems and software are updated and/or replaced and the machine is mechnically repaired and brought up to pass the same "acceptance test procedure" (ATP) - the same test procedure that is done will all new machines. A warranty is included as well. Unlike the demo and new system, refurbished machines are not scheduled and like the demo, are on a first come, first serve basis. 

The Used Bonder: reputable bonder manufacturers NEVER sell used equipment...I repeat...reputable bonder manufactuers NEVER sell used equipment!  Wire bonder, die bonder, and microelctronic packaging machines are highly complex products that require significant expertise and training to run effectively. A good bonder, will in effect "print money" for you. It's safe to say that a used bonder won't do anything for you except take up floor space and collect dust. Those who go down the road of buying a used bonder will find themselves searching for manuals, picking through spare parts, gathering odds and ends from PC boards, coming up with obsolete hardware,  software and componets. Generally, buying a used bonder elimates support all together. Additionally, the software to operate the machine is under license by the manufacturer and you will eventually have to pay a fee to use it, legally. In a lot of cases, used bonder are cannibalized for valuable spare parts or bastardized to meet the specific needs of the past owner.  The only one responsible for the used wire or die bonder plan together is you - I can promise that you would find this task somewhere between duanting and near impossible, or better said, a complete waste of your time. No matter how many cans of new car smell you spray on it, it will always smell like a burned FR4 with a hint of an overheated transformer! 

QUESTIONS?

Contact a Palomar expert to discuss how we can meet you application needs. System purchase or contract manufacturing services together or separately are ideal firms with complex, high reliability applications. 

-Steve Buerki