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Participant joseb10
Participant
701 Views
Registered: ‎01-19-2015

JTAG chain problem

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I had to redesign some boards at work and decided to use the Spartan 7 FPGA FGGA484 package. I followed the user guides and some reference designs from digilent's development boards to have more confidence about it. Fortunately, everything work as expected but I did run into some problems with a couple boards with the JTAG connection.

 

One of the boards didnt recognize the device, but this problem got fixed by resoldering the series resistors between the JTAG pins and the JTAG header.

 

The second board showed the same problem and it also had some soldering issues but could not be fixed by retouching some of the jtag circuitry components. 

 

We do not do the soldering at work, so my question is: is there anything else that I could do on my end to improve the design to avoid soldering problems and possibly for testing the JTAG connections for BGA packages. 

 

I did not know the right way to phrase the question, hope this make sense and I'd appreciate any advice and suggestions.

 

Regards,

Jose Berroteran

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1 Solution

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Xilinx Employee
Xilinx Employee
629 Views
Registered: ‎06-21-2018

Re: JTAG chain problem

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Hi Jose,

 

Xilinx has released Design Guides for BGA packages and, in particular, for the 7 series family:

https://www.xilinx.com/support/documentation/user_guides/ug483_7Series_PCB.pdf

 

Usually, the assembly house and the fab manufacturer will provide certain guidelines that improve the manufacturability of your PCB. You can ask them for that documentation and design using those guidelines as well.

 

You might also want to ask what kind of testing they provide for their boards: X-ray inspection usually catches BGA soldering issues, while ICT does a good job of measuring open circuits, shorts and even measure resistance and capacitance (but can be very expensive for prototypes or low quantities).

 

Thanks,
Andres

 

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2 Replies
Xilinx Employee
Xilinx Employee
630 Views
Registered: ‎06-21-2018

Re: JTAG chain problem

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Hi Jose,

 

Xilinx has released Design Guides for BGA packages and, in particular, for the 7 series family:

https://www.xilinx.com/support/documentation/user_guides/ug483_7Series_PCB.pdf

 

Usually, the assembly house and the fab manufacturer will provide certain guidelines that improve the manufacturability of your PCB. You can ask them for that documentation and design using those guidelines as well.

 

You might also want to ask what kind of testing they provide for their boards: X-ray inspection usually catches BGA soldering issues, while ICT does a good job of measuring open circuits, shorts and even measure resistance and capacitance (but can be very expensive for prototypes or low quantities).

 

Thanks,
Andres

 

View solution in original post

Participant joseb10
Participant
615 Views
Registered: ‎01-19-2015

Re: JTAG chain problem

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Hey andres,

 

Thanks for replying. 

 

I talked to one of the engineers here and yes, we are getting a x ray on that board. Like I mentioned I did follow those guidelines and the problem was only 1/8 boards so far. I was thinking more of a header or something in the layout for a JTAG connection check but again if the BGA isnt solder right I guess that is of no help. 

 

Again thanks for replying

 

Jose B

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