A working knowledge of printed circuit board tolerances can be helpful before electronic product designers approach PCB prototype manufacturers for
PCB assembly services. In PCB manufacturing, tolerance refers to the deviation between the final manufactured product and the intended
specifications at the design stage.
Tolerance is essential for hole (via) sizes on printed circuit boards, as well as spacing, board outline, registration, and thicknesses. PCB manufacturing
companies all work within their own tolerance levels, as stated by each company. That is not to say that the only tolerance level they can work to; the very best PCB manufacturing companies in the U.S., such as Bay Area Circuits, can work to tolerances specified by their customers.
PCB assembly services from Bay Area Circuits
Let's take a look at PCB prototype manufacturer Bay Area Circuits as a case study. We can examine the tolerance levels they work to for the various
PCB assembly services they offer:
Inner layer hole to copper - hole size + 0.020”
Note for PCB designers: Ensure that vias and components can accommodate the copper clearance of 0.010” from a different net.
Board outline: Locational Tolerance - +/- 0.005”
Note for PCB designers: Ensure the outer layer is at least 0.005” from the board edge, and the inner copper layer is at least 0.010” from the board
edge. Allow additional space on the inner layers as they can shift.
Scoring: Locational Tolerance - +/- 0.003” and a Depth tolerance of: +/- 0.005”
Note for PCB designers: Use these tolerance levels and some trigonometry to calculate the closeness between the copper and scored edge. (Be
aware that the center of the score line is the edge of the board.)
Hole Location (annular ring and pad sizing - Tolerance: +/- 0.003”
Note for PCB designers: Plated hole pads must be at least 0.010” larger than plated holes to allow room for an IPC 6012 annular ring.
Hole Size - Tolerance: +/- 0.003” for plated holes of 0.247” or smaller in diameter
Note for PCB designers: +/- 0.002” for non-plated holes less than 0.250” in diameter and +/- 0.005” for larger holes.
Soldermask Registration - Tolerance: +/- 0.003”
Note for PCB designers: Allow at least 0.003” for solder mask clearance between pads (often referred to as “soldermask swell”).
Working to these tolerance figures from PCB prototype manufacturer Bay Area Circuits will ensure that all final assembled boards meet both reliability
and performance standards.
Bringing it all together with completely turn-key PCB assembly services
Suppose you choose complete turnkey PCB manufacturing services. In that case, your chosen PCB manufacturing company takes on the entire end- to-end responsibility: from material sourcing and fabrication to assembly, testing, and shipping (if required). All you have to do is supply a PCB design file, and let your full-turnkey PCB partner do the rest!
PCB Prototyping: Frequently Asked Questions
Q: What is a design review and DFM check?
A: A DFM (Design for Manufacture) checks tolerance levels and flags issues accordingly. A design review can recommend changes to specifications
and ask clarifying questions to the designer.
Q: What considerations do I need to make when choosing materials and planning PCB layers?
A: Tolerance is influenced by material shrinkage, dielectric constants, thermal expansion, homogeneity of prepregs, and panelization layout. Always
design panel layouts to account for edge effects, and plan differential-pair or impedance-control routing with these tolerances in mind.
Q: What Inspection and testing processes are associated with PCB prototyping?
A: Optical and automated inspections check for tolerance deviations, verify outlines, and assess hole positions and thickness. Electrical testing
ensures that all nets are correct and not shorted.
Bay Area Circuits - Your complete turn key PCB partner
Request a price for your next PCB project: www.instantdfm.bayareacircuits.com
Discuss tolerances with Bay Area Circuits by calling: 510-933-9000
Visit the website: www.bayareacircuits.com