New Xmos chip packages

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Folknology
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New Xmos chip packages

Post by Folknology »

The new Xmos BGA 0.8mm chip packages seem rather unusual, the commonly available BGA reballing stencil kits don't tend to include this size I have found. Now unless you are really lucky with your prototypes and the chips go on right first time, every time, having having the right BGA reball stencil is a must. Would it be possible for Xmos to make some of these available, clearly the right stencils for Xmos chips are of interest to all Xmos customers, and I am sure Xmos cold get a good bulk deal on these. Perhaps Xmos could give them away to help make prototyping easier with the new chips or include them with the relevant dev kits? This could help make Xmos development and prototyping with these new chips more approachable?

Just an idea..

regards
Al


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mon2
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Post by mon2 »

Hi Al. As a recommendation, consider the following stencil manufacturer in Shenzhen, China:

http://www.powerstencil.com

Contact: sam_zhong@powerstencil.com

They are the 'best of the best' and firms including Intel, Asus, Gigabyte use them for complex jobs. We have been using them for over a year and the quality + support is excellent. Prices will vary with the stencil size but as FYI, we are paying $ 150 USD for a RoHS compliant and framed 29" x 29" metal stencil for our projects. Their focus is just stencils. Hope this helps.

Kumar
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Folknology
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Post by Folknology »

Kumar thanks for the recommendation they sound like an excellent source for stencils generally.
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lilltroll
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Post by lilltroll »

Hi

I successfully re-balled a XMOS-SU1 yesterday.
We bought cheap balls from China, including general stencils with 0.5mm and 0.8mm ball spacing.
We ordered 0.4 and 0.5 mm balls, but we got 0.5 and 0.6 mm balls so the stencil with 0.4mm holes couldn't be used. Instead I tried to manually place 0.5mm balls and it was much more simple than expexted. I first cleaned the chip with a small (between teeth type of) toothbrush + Isopropyl alcohol. Thereafter I put a little Almit flux and heated the chip just a little so the flux became fluid for a short period of time.
Now I had an even thin surface of flux on the chip. The balls will now automatically align in the pads, since it is a hole in the solder mask on the chip and the balls sticks to the flux. With all ball placed I heated up the chip until all balls became fluid and I was finished.
You will need some optical magnification. I have a microscope, but a loupe should also work.

The 0.5mm balls are larger than the original balls, but I found out it worked very well to solder the chip to the PCB without the need of any solder paste on the PCB pads.

I tried to solder the original BGA balls without any solder paste but I couldn't connect to all pads.

Also a very attractive way to check the connectivity is to use a multimeter in the diode-test mode. Place the positive test probe to GND and put the negative probe to any XTAG2 pin.

When the ball and pads melt together the ports will start to conduct about -0.4V for all power pins and around -0.6V for ports. (At 250 degrees C -0.3 and -0.5V) .

Using 2 multimeters in total, one with a temperature probe taped to the PCB, and the other in the diode-test mode you will see exactly when the pads connect to the BGA.

It is also very easy to check all active pads when the PCB cools down if you have only mounted capacitors and the BGA to your PCB, just use the diode-test mode! You will have to post-mount the inductors if you want to check all pads since the inductor will conduct a DC current.
Since each transistor is a little different 2 balls close to each other should have a different voltage. If 2 balls in proximity to each other give you the same decimals -> you probably have a short-cut!
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Folknology
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Post by Folknology »

Hey nice work Mikael, some useful tips there, where did you source the stencil and balls from out of interest.

regards
Al
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lilltroll
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