Other than a bit of community chatter (much of it contradictory) there is very little easily digestible information on the differences between the Xilinx Flip Chip (FF- LEADED, FFG-LEADFREE) and the Xilinx Lidless Flip Chip (FB-LEADED, FBG-LEADFREE). Xilinx is very good about providing the information needed if you know where to look. We have worked with many OEMs that have used one or the other or both. In this case, you may want to refer to the following Xilinx data sheet and user guide for more details:
Here is a comparison from Avnet showing that the two devices are pin for pin compatible:
Kintex-7 FPGA Device-Package Combinations and Maximum I/Os. Devices in FBG900/FBV900 and FFG900/FFV900 are footprint compatible.
In a nutshell, the better performing FF/FFG should almost always work in place of the FB/FBG, but not vice versa. The lidless chip will often work in place of the FF/FFG, but with limited performance, including reduced max speeds and diminished thermal properties. The FF/FFG enables faster transfer speeds, better thermal properties, and less margin for error. The FB/FBG has a slightly lower initial height but once the thermal interface material (TIM) and heatsink is applied that dimension frequently becomes irrelevant.
The FB/FBG lidless package requires MANY special considerations and here are a few:
1. Component Pick-up Tool Consideration
For automated pick-and-place machines placing lidless flip-chip BGAs onto PCBs, Xilinx recommends using suction cups or soft tips on the nozzles. Failure to do so will cause chipping, scratching, and cracking of the bare die which can render the chip unusable. This may also lead to failures both immediate or later in the field.
2. TIM (Thermal Interface Material)
Lidless Flip Chips require a layer of thermal interface material between the top of the chip and the heatsink. Because the process of applying this material and the plethora of different materials that can be used it creates another variable that exists even inside a homogenous batch of boards. The upgraded FFG (FF) already has the TIM and heat spreader onboard and built to the exacting Xilinx factory specs, eliminating variables and the concerns of damaging or improperly prepping the FPGA.
3. Heat Sink Guidelines for Lidless Flip-Chip (FB/FBG) Packages
Lidless Flip Chip Concerns:
1. Inconsistent or uneven Force applied.
2. TIM with bond line thickness that is not exactly equal.
3. Even slightly off parallel alignment of the heatsink to the top of silicon will damage and/or destroy the chip.
As you can see, improper heatsink placement onto the die will cause damage and render the lidless chip worthless.
Here are some of the upgrade/benefits of the FFG/FF:
1. TIM (Thermal Interface Material) is already resident.
2. Heat spreader lid which has a flat and uniform surface for the attachment of any additional desired heatsink.
3. Superior thermal/heat dissipation properties of the FFG vs the FBG, excerpted here:
4. GTX MAX TOP SPEED
Maximum GTX transceiver data Switching rates
FF/FFG packages support up to 12.5Gb/s from the GTX transceivers, nearly 50% more attainable speed than the FB/FBG packages which support data rates up to 6.6 Gb/s. Below is the comparison in the -1 speed which is still a 20% boost from the FF/FFG should you desire to take advantage of it. The config file will determine the actual speed and if you are already using a set speed you like with FBG, you can leave the config file as is and the speed will not change.
In summary, the primary reason to design in the lidless device is perceived cost savings. However, when you factor in the additional, time, labor, fragility, and other special considerations that gap is diminished. Wouldn't it be great if you could get the top of the line FFG/FF with the onboard TIM and heat spreader and all the added benefits for the same price as the FBG, or less? Here is how that can happen:
XC7K410T-1FBG900I Lidless Flip Chip
Industrial Temp (I) –40°C to +100°C
Avnet screen price: $1,561
Earthtron's price: $775 50% Less
XC7K410T-1FFG900I Flip Chip
Industrial Temp (I) –40°C to +100°C
Avnet screen price: $1,952
Earthtron's price: $755 61% Less
Earthtron can get discounted price on both packages but typically better on the better-performing FFG parts where Xilinx offers both the FBG (FB) and FFG (FF) package. Contact us for savings on ANY Xilinx part including all of the following devices:
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