Beware of unintended and undesired electrical consequences of sockets.
- Current spikes vs. inductance
- High-frequency (and high-edge-rate) signals
- Additional signal skews
- Degraded signal integrity
Without a socket, it looks like a faulty BGA connection would force a write-off on the board and the FPGA.
- With a socket, your design might not work.
- JTAG-based shorts and opens tests (combined with appropriate probe points) should verify absence of opens and shorts, but is dicy for 'weak' solder connections. Nonetheless, it is a cheap and entirely cost-justified test for volume production runs.
- You need to choose an assembly house capable of x-ray checking of correct soldering. Otherwise you are paying for boards which the assembly house has buggered, and you bear all the costs of the assembly house shortcomings. X-ray checking does not improve or degrade initial assembly yield, it helps identify the nature of the failure (for process feedback and repair) and catches failures before you spend a great deal of time in troubleshooting.
- You need to choose an assembly house capable of BGA replacement (no, it should not result in a write-off of the board). The BGA can be recovered with an expensive process called re-balling -- replacement of lost solder balls -- which is justified in the case of very expensive or very irreplaceable devices.
- You need to choose an assembly house with sufficient process expertise and profile control to maintain excellent yield. This should be reflected in a competitive bid for their services, as an assembly house with poor production yield will need to inflate their bid to accommodate the high costs of BGA replacement.
The FPGA i will be using is about $85.00 a pop.
The answer is a fit assembly house, not a socket. Don't forget DFT (Design for Test) and DFM (Design for Manufacturability) practices. Search the web if these terms are unfamiliar.
Quality costs extra, but is often cheaper in the long run. Scrimping on the assembly costs can well be false economy.
If you are kept awake by worries over assembly yield, you have probably chosen the wrong assembly house. A proper assembly house will insist on a properly detailed design review of your board before they bid, and before you order the board fab. If they do not insist, then you have chosen the wrong board house.
-- Bob Elkind
SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369
Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
