How do we assure the quality of your PCB. – part 1

Quality assurance – Part 1 : During Production

Introduction

Quality is not something that is inspected into your PCB. We build it into your boards from the moment you open the price calculator. Our smart menus guide you towards optimum manufacturability. Then PCB Visualizer checks the manufacturability of your specific data-set. We back the quality of your data by preparing the right tooling, using the right equipment, buying in the right materials, designing and implementing the right processing, and hiring and training the right operators. There’s more on this in our video: “How to make a PCB.” Operator training is critical. It is the duty of every operator to check the boards as they go through their process, and we make sure that they have the training and the expertise.

Of course, our fabrication process also include specific inspection and test steps. We use these to make sure that our processes are running correctly. These steps give you the added re-assurance that the board you receive is correct to your design and will perform correctly over the lifetime of your product. These steps are described below.

Standards

We inspect all boards to IPC-A-600 Class 2 This is the standard used for most PCBs, and is the standard most often specified by our customers. The IPC, or Institute for Printed Circuit Boards, is “a global trade association representing all facets of the industry including design, printed circuit board manufacturing and electronics assembly.” The IPC-A-600 standard “describes the preferred, acceptable and non-conforming conditions that are either externally or internally observable on printed boards”. It divides PCBs into 3 product classes. Class 2 includes “products where continued performance and extended life is required, and for which uninterrupted service is desired but not critical.” Class 3 (where uninterrupted service is critical) is used for aerospace, defence and medical applications. For more information visit www.ipc.org.

Customers, especially those supplying the US market, may also specify UL marking. In this case, we further inspect to UL796. The Underwriters’ Laboratory (UL) is “an independent global safety science company …. dedicated to promoting safe living and working environments, UL helps safeguard people, products and places in important ways, facilitating trade and providing peace of mind.” For PCBs, the most important criterion highlighted by UL marking is flammability. All our FR4 material meets UL 94 V0 plastics flammability test. For more on UL visit www.ul.com.

Inspection steps during production.

Front-end Engineering

The first step is to make sure that the data that we will use to make your PCBs is correct. To find out how we do this, go to our blog “Front-end Data Preparation

Fabrication tests

We run 3 types of test during fabrication, visual, non-destructive measurements and destructive tests. The destructive tests are used to check our processes. They are made on actual PCBs or on the test coupons which we put onto every production panel. After more than 30 years of PCB manufacturing experience, we have developed test coupons on the production panels which provide simple, non-destructive tests for more complex parameters.

Each fabrication step can be seen in our video “How to Make a PCB”. The sequence below is based on a multilayer PCB. Single- and double-sided boards do not use all these steps, but are tested in the same way.

Passport

The results of these checks are summarised for each job in its Passport which contains information on the materials used, measurements made and tests passed. You can access the Passport via the blue book icon with each job under View Running Orders once it has been inspected or under Order repeats/View history.

Traceability

If you need more information on a job, we have full traceability back to material batches etc. Contact euro@eurocircuits.com or your local sales channel for this service.

Step 1. Base material.

This is automatically checked against the order details using a data-matrix. The material data (type, manufacturer, laminate and copper foil thickness) is entered into the job history and will appear in the final Passport.

2. Print and Etch inner layers.

Visual checks.

This step includes 3 visual checks:

  1. After printing and stripping to make sure that the unwanted etch resist has been stripped away cleanly
  2. After etching to make sure that all the unwanted copper has been etched away.
  3. At the end of the process to make sure that all the etch resist has been stripped from the board.

Sample check.

Each production panel has a specially developed test coupon which indicates that the board has been correctly etched and that the track widths and isolation distances are correct. The type of etch resist used and the values for track width, isolation distances and annular ring are entered into the Passport file.

3. Inspect inner layer copper patterns.

We use Automatic Optical Inspection equipment to scan the inner layer copper and compare it to the design data. The machine checks that all track widths and isolation distances correspond to the design values and that there are no short or open circuits which will cause the finished board to malfunction.

A Pass is entered into the Passport.

4. Multilayer bonding.

Material.

This is automatically checked against the order details using a data-matrix. The material data (type, manufacturer, pre-preg and copper foil) is entered into the job history and will appear in the final Passport.

Thickness after bonding.

This is measured on each production panel and the result entered into the Passport.

5. Drilling.

The drilling machines automatically check drill diameters to ensure that the size of the holes will be correct. A special test coupon on multilayer boards confirms the position of the drilled holes relative to the (already printed) inner layers.

The smallest finished hole size is entered into the Passport.

6. Hole-wall preparation.

We deposit a layer of carbon on the walls of the holes to make them conductive for electroplating. We enter the process into the Passport.

7. Apply plating resist

Visual checks.

After printing and stripping to make sure that the unwanted plating resist has been stripped away cleanly

Type of resist is entered into the Passport.

8. Copper and tin plating.

Non-destructive sample check.

The operator measures the copper thickness in the holes at 5 or more locations on one panel from every flight bar. The result is entered into the Passport .

9. Outer layer etching

Visual checks.

After etching to make sure that all the unwanted copper has been etched away.

Sample check.

Each production panel has a specially developed test coupon which indicates that the board has been correctly etched and that the track widths and isolation distances are correct. The type of etch resist used and the values for track width, isolation distances and annular ring are entered into the Passport file.

10. Soldermask.

During process.

Visual checks:

  1. Each panel is evenly coated with soldermask ink (laquer)
  2. Alignment of soldermask phototool to the PCB

Sample checks:

The operator uses a projection microscope to check every panel to ensure that the soldermask is correctly aligned and that there are no solder-mask traces on pads.

The adhesion of the soldermask to the surface of the PCB is checked by the tape test used after legend printing.

The type of soldermask ink used is entered into the Passport data.

11. Surface finish

Sample checks on all surface finishes:

  1. The thickness is measured using an X-ray scope.
  2. We check the adhesion of the surface finish to the surface of the PCB using the tape-test after legend-printing.

100% visual inspection.

1. Lead-free hot-air levelling.

The surface must be flat and even across the PCB without any non wetting. Component holes must not be narrowed or blocked. A few via holes may be blocked if they are not covered by soldermask.

2. Electroless gold over nickel.

The finish must cover all exposed copper and have the same colour across the PCB. There must be no discolouration even in the holes

3. Chemical silver.

There must be no tarnishing or blackening.

The surface finish used is entered into the Passport, even where the order is for “Any leadfree”.

For gold and silver finishes we also enter the actual values measured.

12. Component legend.

Sample checks after curing:

The operator makes a tape test to check the adhesion of the surface finish, soldermask and legend to the surface of the PCB. We press a strip of pressure-sensitive tape across the test area and then pull it off sharply. There should be no bits of copper, surface coating, soldermask or legend ink adhering to the tape.

Visual check.

The operator checks that the legend on every board is clean and legible without blurring or smudging.

13. Electrical test.

All boards are electrically tested except single-sided boards where electrical testing is an option.

  1. Shorts and open circuits.

We build a netlist from the Gerber and drill data. We use this as a reference netlist to test all nets are tested for shorts and open circuits. A pass is recorded in the Passport. As an extra precaution, if your design system outputs IPC-D-356A netlist format include the file in your data-set. We can then use this to check the Gerber netlist against your design netlist.

  1. Inner layer registration.

A special test coupon allows us to confirm that the inner layer registration is correct.

14. Profiling and milling.

We check the size and position of the board profile and internal milling using special test coupons.

15. Final inspection.

See Part 2.

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