Table of Contents
Four PCB Assembly Reminders
For smooth and high quality PCB assembly, you need keep four PCB assembly reminders in mind, include parts overage, PCB panelization, break-away tabs and fiducial marks. Here we introduce you all of them one by one.
PCB Assembly Reminders
Parts Overages
“Parts overages” is one of the important PCB assembly reminders, which ensure smooth assembly in only one turn. For PCB assembly flexibility, MADPCB provides Turnkey, Consigned and Partial Turnkey PCB assembly services for your choice. No matter which service you prefer, and no matter who source and provide parts, just keep in mind that all components should have overages because
- There is a small length parts between the feeder and nozzle can not be used
- The pick and placement process may throw away or lose some parts specially at the beginning and the end of PCB assembly
Sourcing or delivering us enough parts quantities will smooth the PCB assembly work and ensure 100% qualified PCBAs will be shipped on time.
The packaging of overages maybe in minimum component packages, like tap and reel, cut-tape, tube and tray. When SMD parts which are not supplied on reels should be on one continuous strip of tapes or reels. Of course, the continuous strips should better have be added a length of leader, like Digi-key Cut-tape. If no leader, MADPCB’s parts uploading technicians will add empty length of tapes to the cut-tapes, and this work will increase labor cost to your PCB assembly project.
But how many extra spares need to provide? Here is a chart of parts overages fore reference.
| Component Size/Type | Need less than 20pcs | Need less than 50pcs | Need less than 100pcs |
| 1206 | Order >=50 | Order >=100 | Order >=150 |
| 0805 | Order >=50 | Order >=100 | Order >=150 |
| 0603 | Order >=100 | Order >=150 | Order >=200~250 |
| 0402 | Order >=100 | Order >=150 | Order >=200~250 |
| 0201 | Order >=100 | Order >=150 | Order >=200~250 |
| 01005 | Order >=150 | Order >=200 | Order >=250 |
| IC, BGA, QFP, Connectors, Large size &Expensive Parts | Order 1-2 more | Order 3-5 more | Order 6-10 more |
This chart lists the overage quantities for prototype PCB assembly. If for high volume with consigned assembly or partial turnkey service, you can consult our team for specific parts overages. Our SMT engineers will reply it to you upon their experience.
PCB Panelization
A larger PCB panelized with one or a few individual PCBs is so called PCB Panel. Unless the short size of your PCB is wide enough, or require special fabrication process, your PCB fabricator and assembler always require printed circuit boards on large panel to improve the work efficiency. PCB panel can only include only one design or multiple different designs but with same layer counts, PCB thickness, copper thicknesses, via constructions, solder mask color, silkscreen color and surface finish. With PCB panels, MADPCB can get all your parts in one turn SMT assembly without any additional setup time. Besides, it also saves customer’s PCB assembly cost with panels. PCB panelization is another of the important PCB assembly reminders, which improves high efficiency assembly work.
There are 3 connection ways to make PCB panel, including
But flexible PCBs, the panel connection should be with tabs between individual pieces PFC, and we will laser cut the rest connection path. The connection can be only a line for laser cut. After PCB assembly, you can depanelize the panels easily. Sometimes, for prototype flex PCB, we suggest to panelize them with “routing” path, which prepares for afterwards mass production when make profiling with die punching technique. In this way, no need make working Gerber twice in future, and can ensure the flexible circuits fabricated are as same as previous prototypes.
Each panelization way has its own advantage(s), while, the boards connection ways will decide the afterwards process, like which PCB profiling technique to use, how to convey PCB on SMT line rail, which PCBA de-paneling technique to use. Both single-up and multi-up PCB panelization will helps to improve PCB production and PCB assembly outputs, but they also have effect on PCB manufacturing cost and PCB assembly cost.
Don’t know how to panelize your PCBs? Just consult our team.
Break-Away Tabs
Break-away tabs, also known as break-away rails, or waste-tabs, which will be broken from the PCB panels and wasted after PCB assembly process or PCBA functional testing process. Can we not add them on PCB panel? No, PCB manufacturers need to add tooling holes, fabrication part number, and other necessary features on break-away tabs to go through fabrication steps.
When panelizing PCBs, waste-tabs on 2 or 4 sides around the panel are ok. How many break-away tabs need to be added? It’s dependent on different PCB designs, like flex, rigid, metal core or rigid-flex, PCB shapes, panel strength, part size and weight, part to outline distance, convenience provided for assembly and afterwards programming and testing.
Generally, the break-away tab width is 5mm, 7mm, 8mm, 10mm and 12mm each side. If panelized by you, you’d better to consult your PCB manufacturing and assembly supplier. In high-volume PCB assembly, “break-away tabs” will be the most important one of PCB assembly reminders to reduce your SMT carrier cost.
Fiducial Marks
Fiducial Marks, or Fiducials are target registration marks that are etched on PCBs, which are used for captured and recognized by CCD cameras of solder paste printer, pick-and-place machine, and AOI machine to ensure high-precision SMDs (surface mounting devices) placement and PCB assembly outcome. In flex circuits manufacturing, fiducials can be also used for position recognition by FPC profiling laser machine.
In panel PCB manufacturing, designers or CAM engineers will add 4 tooling holes and 3 fiducials at the corners of the break-away tabs. In cases with 4 break-away tabs, fiducial marks should be added on the short side because fiducials may be covered by tools if adding them on long side. In cases with 2 break-away tabs, fiducials can only be added on the long side, but need to keep enough distance from the edge of the panel. In SMT assembly, adding fiducial marks is one of the important PCB assembly reminders to guarantee high assembly yield.
If your PCB need double-sided assembly, both top and bottom sides of the PCB should add fiducial marks. The fiducials should be a solid object such as copper with same surface finish as the other copper features on outer layers. Fiducials can be in lots of shapes, but MADPCB prefer circle, minimum 1mm in diameter with 2mm diameter clearance area. No other pads, holes and trances are allowed in clearance area. If the fiducials are located to the cross-hatching copper area, e.g. at its crossing, please remove the crossing in the clearance area.