Introduction
A PCB tab, also sometimes called a printed circuit board tab, refers to a simple rectangular extension of the PCB material beyond the edge of the circuit board. Tabs serve several functions in PCB design and manufacturing.
In this article, we’ll provide a full overview of PCB tabs including their purpose, typical dimensions, placement guidelines, and impact on fabrication and assembly processes. We’ll also describe alternatives to tabs and situations where minimal or no tabbing is recommended for optimal manufacturing results.
Functions of PCB Tabs
PCB tabs primarily serve two roles:
1. Maintaining Panel Stiffness
During fabrication, PCBs are produced in large panels consisting of multiple boards for efficiency. Tabs help keep these panels rigid through all processes. The small tabs bridge the spacing between boards. This retains stiffness that would be lost if boards were completely separated from each other.
Stiff panels prevent warping and damage during shipment and handling. Retained panel strength also allows easier loading and transfer through equipment.
2. Holding Boards in Panel
In addition to stiffness, tabs prevent individual PCBs shifting around or falling out of a panel prematurely before depaneling. Placement of tabs ensures each board remains fixed in its location within the panel matrix.
Tabs must be strong enough to withstand machine insertion forces and acceleration without tearing or releasing.
Typical PCB Tab Design
While tab parameters can vary between PCB fabricators, typical specifications are:
- Width: 0.2” to 0.4” (5mm to 10mm)
- Length: 0.4” to 1.2” (10mm to 30mm+)
- Corner Radius: 0.06” (1.5mm)
- Pattern: Repeating sets of tabs distributed along panel edges
This provides short, robust tabs able to withstand fabrication stresses while retaining board positioning and panel rigidity.
Longer or wider tabs increase strength but use up more board space. Smaller tabs save space but risk tearing during handling. Optimized tabbing balances both considerations.
PCB Panel Tabbing Guidelines
To function effectively, PCB panel tabs should follow certain design guidelines:
- Place tabs at least every 3” to 5” (75mm to 125mm) along edges
- Locate tabs at corners and vocational panel separation lines
- Areas under high router forces require closer tab spacing
- Radial tab sets help hold circular boards
- Larger or thicker boards need bigger, stronger tabs
- Match tab width to router blade width for cleanest cut
Tab placement is designed cooperatively between PCB designer and board fabrication house based on specific panel sizes, shapes, and equipment.
Alternatives to Full Tabbing
In some cases, full tabbing along all panel edges may not be beneficial or even feasible:
Low Tab Density
For simple boards with large spacing, minimal intermittent tabs maintain position without compromising stiffness.
Breakaway Tabs
Rather than rectangular tabs, thin fracturable tabs or score lines work as break points.
Tooling Holes
Round tooling holes used in combination with partial tabs secure panel alignment.
No Tabs
Some panel and board sizes ship successfully without tabbing. Reduces fabrication work.
Specialty Shielding
For metal shielded boards, plated tabs may short shielding. Insulating sections or adhesives are used.
Castellated Edges
Instead of tabs, interleaved castellation along edges maintains positioning.
The optimal tabbing scheme balances panelization requirements, board design, and equipment capabilities between designer and fabricator.
Impact of Tabs on Fabrication
PCB tabs influence considerations across the fabrication process:
Panel Layout
Tab spacing and size affects quantity of boards per panel. Larger tabs reduce panel utilization.
Imaging
Tabs spacing impacts tooling image sizes. Closer spacing allows smaller tools.
Stress
Tabs absorb shear forces rather than boards themselves during handling and drilling.
Drilling
Drill bits must cleanly penetrate any tabs without cracking or leaving residuals.
Router passes slice tabs precisely without tearing or leaving burrs on boards.
Masking
Liquid photoimageable solder mask must coat tab edges without bridging between boards.
Testing
Fixture contacts avoid tabs during in-circuit testing. Ground tabs may impact probing.
Assembly
Components avoid tabs. Tabs considered in pick and place programs.
Depaneling PCBs
Most often tabs get removed along with the rest of the panel remnants during PCB depaneling:
Tab Rout
A final routing pass slices tabs flush with board edges in one action.
Tab Punch
Pneumatic punch dies cleanly snap off tabs leaving smooth board edges.
Break Tabs
Operators manually snap off thin breakaway tabs after routing.
Leave Tabs
Some applications incorporate tabs as part of board, removing unneeded ones.
Depending on tab design, automated or manual depaneling removes tabs after all fabrication and assembly work is complete.
Conclusion
PCB tabs are simple but serve an important role in panelization and fabrication. Appropriately engineering tabs improves manufacturing yield and quality while minimizing space and cost impacts. When designed well in consultation with PCB fabricators, tabs become an indispensable part of efficient panelized board production.
Frequently Asked Questions
Q: What are typical PCB tab thickness?
A: Tabs use the same laminate and thickness as the rest of the boards in a panel. This ranges from 0.005” to 0.125” typically.
Q: Do tabs affect PCB routing density?
A: Intelligently placed tabs route between existing traces so no electrical connectivity is compromised.
Q: How do tabs impact thermal stress on PCBs?
A: Tabs help evenly distribute stresses across panels preventing warpage. Individual boards see minimal effects.
Q: Can solder mask be applied over PCB tabs?
A: Yes, tabs are coated along with the rest of boards. Care ensures no mask bridging between boards.
Q: Are there any electrical considerations for plated tabs?
A: Gold or tin plating can create a short between ground layers if tabs cross internal split planes.
How to Remove the PCBA Break Away Tab
Summary
The article introduces a simple design principle of removing PCBA break away tab. This design can quickly and reliably cut PCB boards of various sizes and pre-engraved with V-grooves. Hope it can help engineering designers.
The development background
PCBA refers to PCB that have been assembled with electronic components and are widely used in various fields such as aviation, numerical control, computers, and automation instruments.
Due to manufacturing and logistics requirements, the edge of the prototype pcb assembly board needs to be reserved, which is not required for the product side. Therefore, the PCBA break away tab needs to be removed after the components are assembled.
The method of removing the PCBA break away tab can be divided into three categories: V-cut depanelizer, milling depanelizer, and manually.
- The milling depanelizer has the best function, which overcomes the limitation that the V-cut can only be linearly divided. The high-speed operation of the milling cutter is used to separate the multiple-connected PCBA according to the pre-programmed path, which improve product quality and reduce scrap rate. The disadvantage is that it is very expensive and cumbersome to operate (programming required).
- The price of the V-cut depanelizer is much cheaper. It is cut along the PCBA V-groove by the blade, but it can only be cut straight, and the cost of the blade is expensive.
3.Manually removing the break away tab is by hand or needle-nosed pliers and other tools for segmentation, with low cost and easy to use, but it is also easy to damage components.
For small batches, multiple varieties and low cost manufacturing requirements, manually removing break away tab is most practical. But for big batches PCBA orders, how could we remove the PCBA break away tab? In order to solve these problems, we have developed a simple tool for manual removal of the PCBA break away tab.
Tooling design
The tooling achieves the purpose of removing the break away tab through a simple mechanical structure, with low cost, which can meet the requirements of adapting to different sizes and thicknesses of the process side.
he tooling adopts the following technical solution: an adjustable auxiliary device for manually removing the PCBA break away tab side, including a mounting base plate, a slider base, a movable slider, an adjustment button, and a transmission structure.
The movable slider is driven to move along the set track on the base of the slider by manually adjusting the adjustment button. After a suitable distance, the process edge to be removed from the PCBA board is placed in the card slot of the device, and finally the PCBA board is held by both hands. The function of manually removing the edge of the process can be realized by gently applying force in one direction below. Please refer to he specific working principle as below picture.
It should be noted that the hands should not be gripped on the top of the PCBA, which is the most labor-saving from the perspective of the principle of the lever, but the stress is also the largest, which is easy to damage the PCBA.
As a preferred embodiment, the mounting bottom plate of the tooling may be a workbench, or other forms of work surface, not limited to the form of the bottom plate; the slider base and the movable sliding block may be a linear bayonet dovetail groove or other The movement fit and the structural form are not limited to various types of movable fits and structural forms; the adjustment buttons may be manual rotation adjustments or other forms of adjustment buttons, not limited to the form of adjustment buttons; the transmission structure may be a cone Gear transmissions or other forms of transmission structure are not limited to the structural form of the transmission.
Compared with the prior art, the tooling has the following advantages:
(1) Low production costs;
(2) Simple operation;
(3) The quality of the process edge is good, and the components on the PCBA board are under stress;
(4) It has a wide application range and can adapt to PCBA boards with different thicknesses and board margins;
(5) The structure is flexible and convenient, and the PCBA board can be manually adjusted to adapt to various thickness and size process sides.
Conclusion
The application of the new manual removal of the PCBA break away tab side auxiliary device not only takes into account the stress control requirements of the PCBA when removing the process side, but also takes into account the cost control of the production. In this way, the tooling can replace the high-cost special equipment, so it is an auxiliary device that is practical, flexible, and can reduce the overall cost, and can be widely used.
