Our assembly prices are based on the assumption that the panel to be assembled contains a single circuit or a step & repeat of a single circuit. We define a single circuit (for assembly purposes) as that assembly where all the part references in the bill of materials (and on the legend) present in the data are unique. There must be no duplication of part references, e.g. multiple "R1's". We must be supplied with single image gerber data which we will incorporate into a panel designed by us, suitable for efficient assembly.
Step & repeated panels for assembly should be kept within a maximum size of around 200mm x 300mm, about the size of an A4 sheet of paper.
Many CAD design packages allow different circuits to be merged into the same panel, and create a single set of gerber data. However, multi-circuit panels created by merging different designs of circuit into a single mother panel create insurmountable assembly problems. There is often insufficient gap between circuits and poor design of break-out tabs make the panels unstable. Part references are duplicated in the BOM and legend. We regret that we are unable to accept orders for the assembly of multi-circuit panels which exhibit these design weaknesses and data errors.
COMPONENT KITS SUPPLIED BY CLIENTS MUST BE CHECKED BY CLIENTS PRIOR TO SHIPMENT
Errors in client supplied kits are the most frequent causes of production delay. Do not trust your component supplier. The component distributor's error rate is over 2%. Do not send us component kits directly from distributors without double checking their accuracy. We may find kit supply errors but we do not warrant that we will. We may not identify wrongly labeled components. An error in a free-issue kit supplied to us is your error. We will fit the parts you supply to us. Rectification costs attributable to wrongly supplied parts are additional to our quoted prices.
Count parts and check that quantities agrees with the BOM, after making due allowance for spares (see below). The identity of each component must be checked against the attached label. Check every digit in the part reference, including the tolerance and voltage rating. Check that the component footprint matches the PCB pads.
You may like to consider the advantages of getting us to supply your components. If we supply kits, we take responsibility for all incoming kitting checks, and we guarantee that the all components will be supplied and fitted exactly as your Bill of Materials. Our buying power may make it more cost effective for us to supply your kit. We will ensure that your selected parts are available through normal distibutor channels. Ask us to quote.
Bill of materials (BOM)
A clear and accurate Bill of Materials must be provided. 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. BOMs must clearly identify parts as either "customer supplied", "PCB Train supplied" or "not fitted". For further advice about submission of your Bill of Materials / assembly data, please click here: http://www.newburyelectronics.co.uk/blog/electronic-design/bom-bill-of-materials-in-7-easy-steps/
Component kits must be supplied with extra (spare) parts to allow for losses and wastage. 5% extra spares is a reasonable guideline for non-passive parts. It is the nature of pick & place machine feeders that parts are wasted at the beginning and end of reels. If we are not supplied with spare parts, we may short ship completed or part built PCBs.
As a guideline, the following fixed minimum quantity of spares should be supplied in continuous tapes. The 5% rule applies thereafter:-
0201 & 0402 - 50 spares
0603 & 0805 - 25 spares
SOT23 (including similar variations SOT23-5 etc) - 10 spares
A/B Tants (& similar size parts) - 5 spares
C/D Tants (& similar size parts) - 2 spares
Due to the variations in prices, the above rules are based on ‘penny parts'. We understand that you may not want to supply e.g - 25 spare 0805 specialist inductors at £3.00 each. In cases like this, please supply as many spares as you reasonably can with any additional bag labelling to indicate high value. We place greater emphasis in caring for expensive small components over cheap penny parts.
Where possible, all SMD components must be supplied taped and reeled. Parts must be supplied in anti-static component bags (generally pink or silver in colour). No static generating materials are permitted on our production floor.
Component packages or bags must be marked as follows:
- Parts list item number and/or location designator (e.g. C5)
- Device description and part reference
- Fine pitch devices must be packed in a protective package to avoid damage legs
- Moisture sensitive devices must be supplied in sealed bags
- Shipping notes must be included with all parts supplied
PCB pick & place data
It is essential to send us component placement data. This data should include:
- CAD x/y coordinate data 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)
We need easily machine readable data with "one reference designator per line", similar to this format:
|Ref Deg||Part No.||Other info / footprint etc|
The format example below with "multiple reference designators per line" is a problem to machine read accurately, and is to be avoided:
|Ref Degs||Part No.||Qty|
Component ident data
Silkscreen, (legend or component ident) data should already be in our possession within the bare PCB manufacturing data package. If not, send the data to email@example.com. A schematic diagram of your layout will assist us to resolve any ambiguities about component polarity and physical placement. Send the data to firstname.lastname@example.org
PCB Train assembly policies
We will use our best endeavours to place all client supplied parts. Clients have responsibility for supplying a clean kit of parts and for any additional costs arising from client supplied component kit errors. In respect of PCB Train supplied Rs and Cs, where non-standard component values are called for (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 labeled 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.
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 different level of quality (perhaps Class 2, or Class 3) for military, medical or other requirements then ask us to quote.
Whilst every effort is made to ensure that you receive a fully functional electronic assembly, we can inspect PCB assemblies at a visual level only. 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 design for assembly
For ease of assembly, the maximum overall size of PCB panel (or pallet) within which smaller circuits are step and repeated, is recommended to be around 300 mm x 200 mm. Larger panels may reduce handling, but over-sized panels cause disproportionate problems of misprinted solder paste, panel bounce during SMD assembly, and management of inspected panels.
BGA footprint pads must be solder resist dammed to ensure adjacent via holes and tracks 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. Do not use the PCB Train Express service for designs containing BGA's because this service does not offer a solder resist. All other PCB Train services include a solder resist as standard.
PCBs supplied by clients must incorporate a handling frame. This is a detachable rectangular frame (made from the same material as the PCB) within which the PCB sits. The handling frame is required so that PCBs with an irregular profile readily fit the conveyors of our SMD mounting machines. Handling frames also ensure that components which overhang the edge of the PCB do not interfere with the edge of the conveyors. When PCBs and PCB Train assembly are ordered at the same time, handling frames are automatically added by PCB Train to the PCB fabrication tooling.