The BOM Says 1,000 Pieces. Why Is the Factory Still Short?
Take a board BOM that adds up to 1,000 pieces of GRM188R71H104KA93D, a 0603 100nF capacitor. Purchasing sees 1,000 and orders 1,000. The arithmetic looks correct.
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Take a board BOM that adds up to 1,000 pieces of GRM188R71H104KA93D, a 0603 100nF capacitor. Purchasing sees 1,000 and orders 1,000. The arithmetic looks correct.
Then the prototype run starts. The warehouse opens a reel, production sets up the machine and checks the first article, and the rework station keeps a small reserve. At the final count there are fewer than 1,000 pieces left. Design, purchasing and production begin asking who ordered short.
1,000 is the fitted quantity, not necessarily the purchase quantity
Two capacitors per board across 500 boards does equal 1,000 fitted pieces. That number answers only one question: how many should end up on the boards. It does not say how many the warehouse needs to support the build.
A prototype and a volume run do not consume material in the same way. A prototype may require opening a full reel, leave leader and trailer tape on the feeder, and use the same batch during setup, first-article checks and rework. The actual extra quantity depends on the equipment, packaging and process. It cannot be guessed from the BOM alone.
Why a blanket 5 percent addition often misses
Some teams add 5 percent to every line because it is easy to administer. But a 0402 resistor and a power inductor do not create the same quantity problem. Small parts may be affected by reel opening and machine setup; larger parts may be driven mainly by the minimum package; some specialty parts should not share the same percentage at all.
The usual result is that inexpensive common parts are over-ordered while the lines that can actually stop the build remain short. Worse, purchasing receives one rounded total with no record of how much was fitted, setup allowance or package rounding, so nobody can audit it later.
MOQ, reel quantity and break-pack terms are different questions
The Kewei product page for GRM188R71H104KA93D lists an MOQ of 100. That means the supplier accepts a minimum order quantity of 100. It does not prove that every reel contains exactly 100 pieces, nor that an order of 137 pieces will always be broken without an extra charge. Full reel, cut tape, loose pieces and a partial reel may have different prices and lead times.
Ask three separate questions: how many pieces are needed for this build, what quantity does the package round to, and can a quantity below a full reel be broken? An MOQ of 100 does not mean the material will arrive in a package that is convenient for the feeder. A supplier accepting an order for one piece also does not mean there is no handling charge.
A substitute part needs a fresh quantity calculation
Two parts with the same package do not necessarily use the same packaging. Tape pitch, reel diameter, quantity per reel, orientation and feeder compatibility can all differ. Twenty pieces left from the original part may cover a repair, but that does not prove the substitute can be bought in the same quantity or mixed into the same reel.
After a substitute is approved, the fitted quantity may still equal board count multiplied by usage per board. The engineering allowance and package rounding must be checked again. Do not copy the original part's purchase total onto the new part number.
Split the BOM quantity into four fields
Use fitted quantity, sample or engineering quantity, planned attrition and package rounding. Put zero where a field does not apply instead of compressing different purposes into one number. If replenishment is allowed, state who approves it and whether the extra material changes the delivery plan.
A workable line could read: GRM188R71H104KA93D, 0603, 100nF, fitted quantity 1000; engineering quantity to be confirmed by the project; planned attrition to be confirmed by production; purchasing to round to the supplier package. Do not enter a number as final before the responsible team confirms it.
Before accepting the quote, confirm MOQ, pieces per full reel, cut-tape support, whether a partial reel can ship, and any packaging surcharge. Purchasing then has a quantity that matches both the BOM and the material package.
The purpose of a precise quantity is not to buy more. It is to know why each part of the quantity exists, buy what the build needs and avoid carrying unnecessary stock. Preventing one line stoppage is usually worth more than adding an arbitrary percentage to the total.
Kewei's take: what this means for procurement
Industry-level changes end up in individual purchasing decisions: lead time, price, alternatives. Following them regularly beats firefighting.
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