When you quote a contract assembly project, the bill of materials (BOM) can make or break your budget—and whether the supplier handles sourcing or you do changes everything. Misunderstanding what's included often leads to surprise costs, delayed timelines, or finger-pointing when parts don't arrive. This guide clarifies how material sourcing works in contract assembly so you can negotiate smarter contracts and avoid costly mistakes.
The Two Main Sourcing Models
Contract assemblers typically operate under one of two approaches: turn-key sourcing or customer-supplied materials.
Turn-key (supplier sources everything): The assembler sources all components, manages lead times, handles inventory, and delivers fully assembled products. You pay a per-unit assembly fee plus material costs, often marked up 15–35% above component cost. This model shifts risk and complexity to the supplier.
Customer-supplied materials: You source and deliver all parts to the assembler's facility on your timeline. You pay only the assembly labor—typically $8–$35 per unit depending on complexity—but you own the sourcing headaches and any supply chain delays.
Some assemblers offer a hybrid approach: you supply high-cost or custom components (PCBs, molded parts), while they source standard fasteners, connectors, or packaging.
Why Material Sourcing Matters to Your Budget
If you're comparing quotes, the sourcing model drastically affects total cost. An assembler quoting $50/unit might include materials; another quoting $12/unit might not. Without clarity, you'll make the wrong choice.
Turn-key pricing looks higher upfront but includes:
- Component procurement (often with volume discounts the assembler passes partly to you)
- Inventory management and storage
- Supply chain risk mitigation
- Single point of contact for delays
Customer-sourced assembly saves cash if:
- You already have supplier relationships and can negotiate better rates
- You're building inventory and can absorb long lead times
- You have internal supply-chain expertise
- Your components are commodity items with stable pricing
For a 5,000-unit run of a mid-complexity electronic assembly, turn-key might cost $75/unit (including $55 in materials). Customer-sourced might run $18/unit (assembly only), but you'll spend 4–6 weeks sourcing, coordinating delivery, and managing obsolescence risk yourself.
Red Flags in Sourcing Agreements
Before signing, clarify these points in writing:
- Material markup transparency: Ask the assembler to break down per-component costs. A 30% markup is reasonable; 50%+ suggests they're not being competitive or they're absorbing risk you don't know about.
- Lead-time responsibility: Who owns delays if a component is backordered—you or the assembler? In turn-key deals, this should fall on the assembler.
- Minimum order quantities: Some assemblers require 1,000+ units before they'll source specialty parts. Verify this doesn't exceed your needs.
- Excess inventory: If you order 5,000 units and the BOM requires 5,050 components (accounting for scrap), who pays for the extra 50? Get this in writing.
- Obsolescence and price adjustments: Semiconductor shortages and material price swings are real. Will your unit cost adjust mid-project if component costs spike 20%?
Questions to Ask Before Committing
- Is sourcing included in your quote? Don't assume. Ask for an itemized breakdown: assembly labor, materials, overhead, shipping.
- Do you offer consignment inventory? Some assemblers will hold materials you source on-site, reducing your logistics burden while they handle assembly.
- What's your typical supplier lead time for standard components? If they say 2–4 weeks, confirm they can meet your project deadline.
- Will you guarantee material quality and component authenticity? This matters for regulated industries (medical, automotive). Reputable assemblers source from authorized distributors, not gray-market suppliers.
- What happens to unused materials after assembly? Can you return them, or does the assembler keep them?
How to Compare Quotes Fairly
Get three quotes and standardize them around the same BOM:
- Request per-unit assembly costs (labor only)
- Request itemized material costs for 3–5 key components
- Ask total landed cost including shipping to your facility
- Note lead time and minimum order quantity for each
If sourcing is included, verify the assembler sources from reputable distributors (Arrow, Heilind, Tech Data for electronics; verified industrial suppliers for mechanical components).
Frequently Asked Questions
Q: Should I always choose turn-key sourcing to save time? Not necessarily. Turn-key is fastest if the assembler has established supplier relationships, but if you already source materials and have long lead times baked into your project timeline, customer-supplied can be cheaper and give you more control.
Q: What if my components arrive damaged or defective before assembly? In turn-key agreements, the assembler bears this risk and replaces parts at no cost. In customer-supplied models, you own the risk unless the damage occurs at their facility—which is why you should photograph items upon arrival and have the assembler sign off on condition.
Q: Can I mix sourcing—provide some parts and let the assembler source others? Yes, and it's increasingly common. Discuss which components (by cost, criticality, or lead time) you'll supply and which they'll source, and ensure the contract specifies who's responsible for each.
Find vetted contract assembly providers who match your sourcing preferences—turn-key, customer-supplied, or hybrid—on Mercoly, where you can compare quotes and timelines side by side.