LESSONS LEARNED IMPLEMENTING CHIP-ON-BOARD
Jeannette Plante,
Swales Aerospace,
(301) 572-8649
jplante@swales.com

Last year NASA Headquarters Code Q began a task to demonstrate the feasibility of building an ultra-small command and data handling (C&DH) unit for satellites using chip-on-board fabrication techniques. A parts list was produced by the designers and sources and prices for the parts, in die form, were researched. The results were somewhat disconcerting in that the minimum buy requirements and lack of available product drove the cost of the parts beyond $800,000. This article shares some of the lessons learned during the procurement cycle.

The first approach was to get quotes for known good die (KGD). In most cases, either KGD were not available at all or KGD product was only available by special order with as much as a $15,000 lot charge for non-recurring engineering costs (NRE). A MIL-PRF-38534 element evaluation approach was quoted by one distributor at $5100 per lot (for a 100 piece minimum buy) with no guarantee of a single lot per order. Many quotes were received with no details about what testing, if any, would be performed. Two part types would not be sold by the manufacturer in die form.

Minimum buy requirements were also problematic. Minimum buys of 100 pieces were required by distributors for mature, rad-hard parts. Rad-hard parts which were available only from the original vendor, had minimum buy quantities in the 20 to 50 piece range.

Table 1 below shows the first cost estimate for 80% of the parts sought in die form. Quality levels vary between "unknown" and KGD.

Table 1
Description
Quality
Minimum Buy Quantity
Cost
Microprocessor unknown 
100
 $434,815
128k x 8 EEPROM unknown 
1000
 $ 36,000
128k x 8 SRAM QML line 
50
 $136,750
Line Driver Lot Acceptance Test 
100
 $ 35,690
Line Receiver Lot Acceptance Test 
100
 $ 35,690
Schmitt Trigger Lot Acceptance Test 
100
 $ 8,571
1553 Controller KGD 
20
 $ 84,300
1553 Transceiver KGD 
20
 $ 52,500
Octal Buffer KGD 
100
 $ 1,642
EDAC Lot Acceptance Test 
100
 $ 44,870
EDAC Limited functional testing at wafer level 
5 wafers
 $ 17,920
TOTAL
 $888,748
Given that the budget was about an eighth of the figure shown in the table, the project was forced to find alternative ways to procure the die. Some part types were changed to tap into lower priced technologies. Excess inventory at hybrid manufacturers was sought. Testing requirements were reduced.

The final C&DH hardware will be a hybrid of chip-on-board and packaged parts. The procurement activity was a valuable learning experience for NASA for future use of chip-on-board. One obvious solution seems to be common-buy procurements, though this can be logistically unworkable and ineffective if the common programs are not buying enough of the same part types or have significantly different build schedules.