In our earlier blog, we explored what scrap is. We also looked into how to account for it when purchasing various types of components. In this blog, we will explore the process of purchasing components. We will find reliable sources. We will ensure the quality of components before starting PCB assembly. Additionally, we’ll discuss the key factors to consider after receiving the components to ensure a smooth assembly process.
Part purchase guide:
1.Please prepare a BOM, ensure it includes the below details:
- Part Number (MPN): The manufacturer-assigned part number.
- Manufacturer Name: The name of the part's manufacturer.
- Quantity: The total number of parts required.
- Designators: Component identifiers (e.g., R1, C1) from your schematic.
- Specifications: Important details like voltage, tolerance, or package type.
Refer to Fig. 3a below for an example of a properly formatted BOM. This format was also discussed in detail in an earlier blog post. Make sure your BOM is clear and thorough to avoid any procurement or assembly delays.
In a typical BOM, the quantity listed is usually for 1 piece of the assembly. You can verify this by checking the count of designators. For example, in the BOM above, on line No. 3, there are four different designators: R6, R7, R8, and R9. All of these use the same MPN: CR0603-FX-4990ELF. This means that in one assembled board, CR0603-FX-4990ELF is used in a quantity of 4.
If you want to produce 50 assembled boards, you will need 4 x 50 = 200 pieces of the MPN CR0603-FX-4990ELF. Additionally, you should account for some extra parts to cover for scrap (as discussed in an earlier blog). Therefore, the total purchase quantity for MPN CR0603-FX-4990ELF will be [(4 x 50) + Extra].
2. Need to prepare full bom for purchase quantity as described above. Refer to Bom Below as fig.4a .We have added purchase quantity for whole bom. We have taken Extra as to just illustration purpose only, we have not counted as per actual assembly requirement. Also we have hidden some raw to batter view of table to shows purchase quantity for 50 pcs assembly.
3. Now, it’s time to decide on a supplier for your required components. Always focus on choosing a trusted supplier. There are many reputable online part suppliers, like Digi-Key, Mouser, Arrow, Future Electronics, Element14/Newark, TTI, and others. Additionally, don’t overlook the value of local suppliers. Local suppliers can be helpful for quick and reliable delivery, often providing same-day service for urgent orders. They are also a cost-effective choice.
Most online suppliers offer a feature where you can directly upload a Bill of Materials (BOM) with your required quantities. Once uploaded, it will add the items to your cart. You then simply need to give your shipping address, make the payment, and you're done!
Important: Don’t forget to include your reference number when uploading the BOM. This reference number will be printed on the part bag labels. It will make it easier for you to find the parts upon delivery.
The label typically includes important details like:
- MPN (Manufacturer Part Number)
- Designators
- Quantity
- Manufacturer
- Customer Reference Number
- Supplier Part Number
The specific details vary depending on the supplier.
4. Before making the payment, please double-check your final cart. Some parts might have a long lead time, limited availability (partial stock), or could even be obsolete for new batches. In such cases, choose alternate parts that meet your design requirements. Alternatively, explore other suppliers to source out-of-stock or partial-stock items.
Many online supplier tools can help you find suitable alternatives. For example, here's a quick video tutorial on using the Digi-Key website to find alternate parts.
Don’t forget to subscribe to my YouTube channel for more helpful content!
5. Once the parts are received, you need to verify them against the BOM. Check the following:
- Quantity
- Damaged packaging
- Damaged parts
- Wrong parts
- Part labels
- Documentation for critical parts, such as COC (Certificate of Conformance) and other relevant documents
After verifying the parts, arrange them with proper labeling for assembly. Store the parts in a safe location, ensuring they are protected from ESD (Electrostatic Discharge) damage.
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