PCB Assembly Technical Advice
PCB Pick & place data
Where possible, send us component placement data. This data should include:- CAD x/y coordinate data should be in .prn, .csv, .xls, or other editable format.
- CAD x/y data must contain columns that include:
- part number (e.g. 1206100NF)
- reference designator (e.g. C12)
- x /y coordinates
- theta rotation angle (e.g.90 deg.)
- placement surface (e.g. top or bottom)
Assembly Parts list or bill of materials (BOM)
- a clear and accurate Bill of Materials is essential for each pcb.- it is invaluable for clarity to include Farnell part numbers.
- different types of components should be listed in groups, i.e. 0805 10nf’s sequentially, then 0805 100nf’s etc.
- component values should be clear e.g. 100R, 100K, 100M etc, and not just “100” printed as the value.
- identify parts on your BOM as either “customer supplied”, “PCBTrain supplied” or “not fitted”.
Silkscreen, legend or component ident data
This data should already be in our possession within the bare PCB manufacturing data package. If not, send the data to cadcam@newburyassembly.co.uk A schematic diagram of your layout will assist us to resolve any ambiguities about component polarity and physical placement. Send the data to cadcam@newburyassembly.co.uk
Component Presentation
- never send the exact component quantity. We always need some spares to make up the inevitable losses in production. Without extras, we will short ship completed pcbs.- supply at least 5% extras of each component to act as spares. We will return any surplus with your assembled circuits.
- where possible, SMD components must be supplied taped and reeled. Allow extra parts for feed-in and feed-out on the SMD assembly machines.
- use anti-static component bags (generally pink in colour). No static generating materials are allowed on our production floor.
Component packages or bags must be marked up with:
- parts list item number and/or location designator (e.g. C5) - quantity
- device description and code
- fine pitch devices must be packaged to avoid damage to their legs.
- moisture sensitive devices must be supplied in sealed bags.
- shipping notes must be included with all parts supplied so that we can check that the contents is correct.
PCBTrain assembly policies
- where devices are requested that may not be a standard value (e.g.123 ohms), we will fit the nearest E24 value such as 120 ohms. - customer supplied components that do not correctly fit the PCB footprint will either be modified to fit (if economic) or returned unplaced with the assembly.
- badly labelled components that cannot be cross-referenced to the parts list will be returned to clients with the assembly.
- if an unclear drawing and/or placement diagram is supplied, we will attempt to contact you and ask you to clarify the information.
- parts with ambiguous placement locations may be left unplaced and returned with the assembly.
Quality
We will build your Printed Circuit Boards to standard commercial quality (using specification IPC-A-610 Rev C – Class 1, Acceptability of Electronic Assemblies) as a guideline. If you require a higher level of Newbury Electronics Ltd PCB-Train Assembly Guidelines & Policies of February 2006 (Issue 3) quality (class 2, or class 3) for military, medical or other strict prototyping applications then please contact us for a quote. Whilst every effort is made to ensure that you receive a fully functional electronic assembly, we can only inspect pcb assemblies at a visual level. If a fault is subsequently found as a result of an assembly error then we will rework the assembly without charge.
A no-clean 2% silver loaded solder wire will be used for all hand assembly. The colophony- free flux contained within this wire will leave a slight “white-powdery” inert residue around the solder joints. This is non-corrosive and is acceptable within most commercial applications.
PCB / Assembly Design
BGA footprint pads must be solder resist dammed to ensure adjacent via holes do not wick solder away from the solder ball. Do not put via holes in BGA pads or indeed in any SMD pads. Via holes should be tented or covered with solder resist especially under BGA's to avoid solder paste wicking.
