I was on the shop floor and noticed deflection in the 8x8 inch panel being populated. Would the deflection in the middle of the panel cause components to sit higher on the paste and thus have a slightly higher solder joint height than components near the support rails? Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis.
He has vast experience in SMT equipment, materials and processes.
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics.
He is a pioneer in the science of reflow.
Transcript
Phil
Welcome to Board Talk! This is Jim Hall and Phil Zarrow of Pick and Place - the Assembly Brothers. We actually have a Pick and Place question today! How appropriate!
Jim
This comes from D.H. I was on the shop floor and noticed deflection in the 8x8 inch panel being populated. Would the deflection in the middle of the panel cause components to sit higher on the paste and thus have a slightly higher solder joint height than components near the support rails?
Phil
Whoa, deflection!
Jim
The bottom line is deflection is not good in any process.
There are two concerns here. Is this deflection in the board by itself just sitting on the conveyor system before it's being populated? Or is this deflection that's occurring because of the Z-axis forces of the placement machine? And I'll say it right now - neither one is any good.
Phil
It's a bad situation either way. One of the worst causes would the deflection caused by the Pick and Place head coming down. And there's a number of things going on here. Typically, that would be any improper Z-axis location, or excessive Z-axis force due to a programming error. If that's it, it should be rectified right away.
Besides potentially smashing your component, you're probably displacing solder paste. I wouldn't be surprised if you see solder balls or inadequate solder joints.
If we're talking about just the board from a support standpoint, well Jim?
Jim
If the board is deflected by itself - without the placement forces, then it's really up to your placement machine. Some of them can correct for this using force sensing to place the component.
You need to support your boards during placement, also during printing, and also during dispensing. And to some extent during reflow because deflection of the board is not a good thing.
In printing or placement it can cause errors such as Phil just described, paste getting squished out underneath causing solder balls. If the deflection is down in the middle, and the placement head doesn't compensate for it, you can get parts sitting on top of the solder paste not properly inserted into the paste. That's a recipe for tombstones on chip components, and potentially a poor wetting or opens on any component.
So you want to look at developing proper board support throughout your placement operations.
Phil
So, D.H., on your Pick and Place machine, check out that parts' smashing operation and make sure you've got adequate support.
Jim
That this is a universal problem that we see throughout the industry and our consulting business. People just don't have support fixtures, or they don't put them in. They don't put the pins in the right places and it introduces variability.
Phil
So this is Phil Zarrow and Jim Hall - Pick and Place of ITM Consulting saying thank you.
And whatever you do, don't solder like my brother.
Jim
And don't solder like my brother.
Comments
I see three factors that need to be checked.
Board supports. There should be very little give across the board
Component height taught for the program as Keith mentioned above. If the height is taught a little lower than it is supposed to be it will drive the part in the paste
Is the machine height calibration correct?
We also have another safeguard in our machines with small springs in the nozzles to give it that little extra play instead of driving it into the board and either going to deep in the paste or cracking chips etc...
Chris Ellis, Manncorp
The Europlacer IINEO machine has a patented, award winning 3 Dimensional Positioning System (3DPS) that reacts to Z height and adjusts placement pressure automatically, putting a perfect amount of force on every placement, whether the board is warped up or flexes down. Boards as thin as 020 can be placed reliably, without board support if you choose. It also helps when picking, whereas Z & pick height does not matter to us. (*a change in z up to 1/4" is automatically compensated for by the turret head) See www.europlacer.com for more info on this or our 5 year warranty.
Chris Merow, Europlacer
I agree with Mr. Bernhard's comment re: automatic tooling. Our shop uses Quik-tool products extensively. Since their introduction, we have seen decreases in the defects discussed in the article (tombstoning, solder balls, damaged components, poor wetting, etc.)
Jim Blundon, Whelen Engineering
When I see deflection, I first check the programmed component height. If the machine thinks that a component is shorter than it actually is, then then it tries to push the component through the board. This could crack a component. Once the board is deflected, it tends to spring back which could throw small components off.
Keith Dael, Tetrad Electronics, Inc., USA
There are exceptions, but in general, the final height of the soldered component is largely controlled by wetting and buoyancy forces while the solder is molten. Therefore, deflection of the board during component placement should cause little or no variation in soldered component height. In fact board deflection may help to compensate for excessive placement force by lowering the impact force on the component during placement.
Tom Salzer
Automatic support tooling may be a good solution for you. This type of tooling conforms to the bottom-side, components and all, and supports the board during placement (and printing). With no programming required, it could be an easy implementation to solve your problem.
