PCBA--Common factors that affect the efficiency of Assembly service.

a. BOM doesn’t include Part Numbers:

In order to provide exact stock and price to components, Part Numbers are needed to be listed in BOM, either Manufacturer Part Number or Distributor Part Number is acceptable.


Add exact part numbers to BOM to get accurate components price and stock information. For more elements of BOM, please click below link to get the example BOM for reference.

b. BOM doesn’t include components references (designators)

There is no component reference (designator) in BOM uploaded, which may affect assembly cost presented. Because assembly cost depends on the total amount of components. We will check if references numbers matches quantity listed in BOM.


Add components references (designators) to BOM to get accurate assembly price. For more elements of BOM, please click below link to get the example BOM for reference. 

Components with same part number are not listed in same row. For example:


Suggestion: List same components in same row like below,



d. Information in BOM are not consistent.

For example, part number and description don’t match; quantity and designators don’t match; part number and footprint don’t match (Part in BOM is SMD but pads on PCB are for THT).

e. PCB layout doesn’t support components.

For example, through holes are designed too small, holes tolerance and component size tolerance is not considered which causes soldering not possible.

f. PCBA files are not completed.

For example, no pick&place (centroid) file; no silkscreen on PCB; no polarity or orientation marks on PCB; designators in BOM don’t match the ones in pick&place file (assembly is based on part numbers and designators in BOM, part numbers and designators in pick&place file is just for reference).

 g. Special soldering notes for some components.

There are some different types of LEDs, like top view LED and side view LED. You should provide exact LED part number in BOM. If LED in BOM is top view but pads on PCB are for side view LED, then assembly can’t be arranged by SMT machine, it has to be proceeded manually, which will increase assembly cost and assembly time.

 h. No comments to sensitive components.

For example, some LEDs are very sensitive that require special temperature in storage and soldering. We suggest do function testing to boards after assembly is done in order to avoid bad LED soldering.


 Note: Special requirements in BOM.

1). Components should be purchased but no need to be soldered to PCB.

2). Components should not be purchased or soldered so you can mark them as DNP or DNS.

3). Special temperature requirements to soldering of some sensitive switches, LEDs or connectors.

4). Leave some gap between components and PCB surface.

5). No need to cut pins of some THT components after assembly is done.

6). PCB can’t be washed by ultrasonic due to some sensitive components.

7). Components can’t be reflow soldered.

Leave a comment

Please note, comments must be approved before they are published