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Product category: Electronics Manufacturing Quality Assurance
News Release from: Blundell Production Equipment | Subject: Ersascope
Edited by the Electronicstalk Editorial Team on 30 September 2003

BGA inspection demands a closer look

Paul Cooper, Product Manager at Blundell Production Equipment, explains why visual inspection is preferable to X-ray analysis in evaluating BGA joints.

Paul Cooper, Product Manager at Blundell Production Equipment, explains why visual inspection is preferable to X-ray analysis in evaluating BGA joints What problems are you seeing with your BGA assembly and soldering process

Well some of you are not seeing at all, at best you may be relying on someone's evaluation of a grey image from X-rays to determine whether your process is under control or not.

Let me tell you that a good majority of BGA joints that we see, using the Ersascope, you would not accept elsewhere within your process.

If you saw solder joints on gullwing devices that where dull or grainy you would modify your process until they became clean, bright and smooth.

Why? Because you know that anything other than this is likely to end in premature joint failure due to poor intermetallic bond.

More can be determined from the surface finish of a solder joint than by any method other than taking a micro-section.

And that is not exactly a convenient online method.

I would guarantee that if a poor BGA joint were to be put along side a good one most engineers would be able to identify the good one, and without exception, all would say that this is no less than they should accept.

After all, this would be the criterion for any other solder joint.

So why have we accepted a different set of rule for BGAs? Well to be fair prior to the arrival of the Ersascope there was very little alternative, X-ray analysis had become the clever but expensive solution to a difficult problem.

But just what can it tell you about your solder joint? It will tell you that you have a solder ball in the right place mounted correctly on your PCB.

It will tell you that you have no solder shorts.

It may identify flux inclusion.

And the more expensive ones with highly skilled operators will be able to judge whether the solder balls have dropped.

What has it not told you? Well, although a 3D X-ray image can identify a solder drop it is unlikely to be able to identify between a single drop (solder melt) and a double drop (formation of intermetalic bond), and actually it has told you nothing about the joint itself - the very element that ensures the long term reliability of your product and ultimately your company's reputation.

You cannot rely on the fact that because you achieve a good solder joint on a J-leaded device that the same profile will produce an equally good joint under a BGA.

In most cases you will need a different profile to ensure a good joint under a BGA simply because the mechanics of the device are different - the accessibility for hot air to move around under the device and the thermal conductivity both differ from the other devices on the board.

But all these factors are taken into account when you can visually inspect to joint level and adjust your process accordingly.

The Ersascope has become a worldwide phenomenon in the industry.

It provides the visual opportunity to look under, not only BGAs or uBGA devices, but all the others on which you currently have to make assumptions simply because you cannot see.

Now you can view a cold solder joint, a single drop or scaled joint.

You can see the fillet on the underside of most connectors, whether through-hole or surface mount.

This enables you to modify your process so that you can be absolutely sure that your hidden joints conforms to every other joint on the board before you finally lay down your process.

And, you can quickly and easily establish that your process remains under control by periodic checks, just the same way that you do with all the other joints on all other devices.

In addition, the Ersascope software leaves nothing to chance.

There are currently hundreds of reference images of joints - some good, most are unacceptable - that allow you to make the correct decision as to your live image joint quality and ultimately your process.

Once you have identified a reference image similar to your live image, and both can be viewed on the screen at the same time, then the "problem/solution" database will enable you to: define the problem; provide documented information as to its cause; and give a detailed explanation of how to solve the problem within your process.

And as if this is not enough it will also measure linear height, width, circles or angles to an incredible accuracy of better than 1.0um.

Using x350 magnification at the lens and a further 800% digital magnification within the software, you can check such things as solder paste deposit - not only for shape and position but size and volume.

You can even check the ball size of solder paste to ensure your supplier is within agreed tolerances.

All images can be saved to file, printed in hard copy or sent via e-mail.

There are few limitations to the Ersascope and its Image-doc software.

Particularly as far as visual process control and measurement is concerned, which is probably why it remains the world leader after three years.

Its flexibility, ease of use, and image quality remain second to none with no hidden or consumable costs to consider.

Systems cost from under GBP 10,000, and free demonstration CDs are available.

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