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Lot Genealogy PDF Print E-mail
Written by Aparna Joshi   

Lot Genealogy: This is a very common term used in semiconductor industry. What does it mean exactly. I am going to try my best to explain this.

Let's start from a packaged part, that means an IC chip which is being shipped to the customers. To begin with, let's consider a simple example of single module chip. If I break this chip, I see a die, connectors and connection pads inside. This die comes from a wafer which was diced along the scribe lines. This wafer may have thousands of dice depending on the size of the wafer and the die. The wafer belongs to a lot. A lot may have upto 25 wafers. This lot comes from either a vendor fab or from a in-house fab.

When a lot is started in the fab, it gets a identification number. Each wafer in the lot gets its own identification number. As PCM data gets collected immediately after the wafer is fabricated, it has this fab lot and wafer identification numbers. Let's call this lot number as ABC123.

This lot is then shipped to the probing facility. It can be a vendor or in-house. In either cases, this lot gets another identification number. Now, the lot ABC123 becomes PQR456. Now, wafer probe data has this new lot identification number.

After probing, the lot is sent to packaging. Each wafer gets diced into individual chips. Depending on the number of dice on the wafer, packaged parts are split into multiple lots for testing. Each lot gets a unique identification number. PQR456 is split into 4 new lots XXY123, XXZ234, XYY345 and XYZ456.

Lot Genealogy data must link XXY123, XXZ234, XYY345 and XYZ456 lots to PQR456 lot because wafers for these lots came from PQR456 lot. PQR456 lot must link to ABC123 lot as all the wafers came from that fab lot. A collection of all these links is Lot Genealogy Data. Unless we get this data, it is impossible to correlate PCM data, probe data with final test data. This correlation helps resolve yield loss or causes of customer returned parts.

This data is more useful when a chip has multiple modules. That means final packaged parts has multiple dice for various functions. Now, instead of one wafer lot, we must link multiple wafer lots to these final parts lots.

Let's consider Part A is composed of d1, d2, d3 and d4 dice. d1 comes from G123 lot, d2 comes from H123 lot, d3 comes from I123 and d4 comes from J123 lot. As they are different parts, their fab lots are different too. Their fab lots are L111, M111, N111, S111. One wafer of each module supplies to all four final packaged  XXY123, XXZ234, XYY345 and XYZ456 lots.

A complete Lot Genealogy data will consist of the links to L111, M111, N111, S111 and G123, H123, I123, J123 and XXY123, XXZ234, XYY345 and XYZ456 lots.

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