The FT87C257 A Custom UVEPROM Solution

UVEPROM. This is the first of many product blogs, in which I will be talking through the development process from initial requirement to finished solution. In this post I will be discussing the manufactured solution to replace the 256K (32Kx8) UVEPROM the customer requested.

The initial request was for an LD87C257 device with an operating temperature of -40°C to +85°C and additional Dynamic burn in for 168 Hours ±8 at 125°C. Our initial investigations showed the original product utilised CHMOS which was the Intel CMOS process developed from their HMOS process (with the H standing for high-density). It also incorporated an addresses latch on the address pins to minimise chip count in multiplexed bus systems. This allowed circuit designers the option to eliminate an external address latch by tying address and data pins of the 87C257 directly to the processor’s multiplexed address/data pins.

FTs approach has always been to offer the customer the most cost effective solution. Unfortunately the desire for the address latch prevented them from using our off the shelf 256K UVEPROM (The FT27C256R) as it does not have this functionality.

It was confirmed through our qualified supply chain, that less than 50 pcs were globally available in any package and no stock of the original device in die form existed. This pushed us to examine potential alternatives and device redesign. An alternative obsolete device was found manufactured by National semiconductor which had the same address latch feature as the requested Intel device.

Whilst the National Semi device was also obsolete, enough stock was available to fully support both the short and long term customer  requirements. The package available was the one-time programmable variant (a PLCC Package). After further discussions with the customer we provided a quotation to remove the die from the available PLCC package (via our die reclamation service which you can read more about here), assemble it into a windowed CERDIP and test as per our SCD (source control drawing) which was built around customer requirements.

The National NMC87C257 Die

After receiving the PO we begun extraction of the die from the PLCC Package  and made a die pad layout in parallel from the existing bonds. A bond pad layout was drawn up and the lead frame was secured to the base of the package ready for die attach. The die was secured using JM7000 die attach material and once the bonding was complete the lid was fixed in place and sealed. Force maintain a working stock level of the original windowed CERDIP packages and lead frames, the windowed lids in particular are very difficult to source in today’s market due to the obsolete nature of UVEPROMs.

The finished the device was then programmed and subsequently UV erased to ensure the solution had been a success. Further functional testing was performed to ensure the device functioned to specification parameters and they met the tACC value required by the customer. Devices comfortably passed a Dynamic burn in for 168 Hours ±8 at 125°C and the final functional verification test over -40°C to +85°C temperature range.

Some finished product ready for shipment