Eurocircuits Technical Update – direct imaging technology

In this update

  • New direct imaging technology – more capacity, more design options
  • 2015 – a record start to the year
  • Medium-volume BINDI pool now UL approved – and 4 layers soon
  • Eurocircuits sponsor student projects

Direct-imaging technology

MORE CAPACITY

The Ledia V5 direct-imaging system, installed in January, is our largest single investment in a single piece of equipment – and is already paying off. Direct imaging has boosted our production capacity in time to handle the fastest growth in orders we have seen in years. See how it works in our technical BLOG.

MORE DESIGN OPTIONS

The reliable assembly of new-generation BGAs, QFNs and fine-pitch leaded components demands tighter-toleranced soldermasks. Ledia images finer soldermask dams than conventional phototools. We will use it in conjunction with our forthcoming solder-bridge pre-CAM tool to produce the optimum soldermask solution for your designs.

2015 – a record first quarter

Q1-2015 we served more than 5,500 customers with almost 24,000 orders. Thus we are up 15.8% and 18.5% on the first quarter of 2014. And 2014 was already a record year.

BINDI pool news

  • Our BINDI pool service for orders up to 50 m2 is now UL approved. UL marking can be added to your boards at no extra cost
  • From May BINDI pool will offer 4-layer multilayers as well as 2-layer PCBs

Student project sponsorship

We have sponsored student projects across Europe for many years as part of our commitment to foster new generations of electronics designers. See our BLOGS for some recent projects. If you are looking for sponsorship for a student or educational project, contact us at euro@eurocircuits.com.

Technical blogs

Some recent highlights, all now available in English, French. Spanish and Portuguese:

If you would like us to produce a blog or white paper on a particular aspect of PCB manufacturing technology, PCB soldering or EAGLE CAD, email us at euro@eurocircuits.com.

Meet us

The best way to share ideas and knowledge is face to face. Come and meet us at:

How do we assure the quality of your PCB – part 3

Quality assurance –  Microsection analysis

Introduction

Microsectioning or cross-section analysis is a destructive sample testing procedure, used throughout the PCB fabrication industry. We make regular microsections each day, as they allow us to see inside the PCB and make precise measurements to check our production processes and to confirm the quality of the finished PCBs.

We use microsectioning to check the quality of:

  • PCB base material
  • inner structure of multilayer boards
  • plating in plated-through holes
  • thickness and registration of external and internal conductors
  • connection between the layers
  • soldermask cover
  • surface finish thickness

Microsectioning procedure

  1. Select the appropriate PCB or quality-control test coupon
  2. Cut out a piece for sample
  3. Embed the sample in resin
  4. Grind down to a flat surface
  5. Polish and etch back if needed

Multilayer build checking

We check the build-up of the multilayer PCB, the thickness of the cores, copper foils and prepregs, and the effectiveness of the bonding process. We also look for any defects in the laminate after thermal stress (delamination, blistering, voids or cracks etc.)

We inspect the registration of inner copper lands to the holes. The next picture shows the same PCB as the last one, but when we measure the registration of the hole to the inner layer copper we see that there is some misalignment (in this case within tolerance).  We also use a special test coupon on all multilayer production panels to confirm the position of the drilled holes relative to the (already printed) inner layers.

There should be a robust connection between the wall of the plated through hole and the inner layer copper as shown in the next picture.  A poor or broken connection points to process issues in drilling or hole-wall cleaning.  A broken internal connection on a finished board would be caught by electrical test.

Through hole plating

We make 5 non-destructive measurements of the thickness of the plated copper in the holes on every production panel.  We back this up with regular microsectioning to get more information about process quality. For this we use the test coupon which we put on every production panel.

The plating thickness is the average of six measurements taken three on each side of the hole roughly a quarter, a half and three-quarters down.

Our standard tolerance for component holes is +/- 0,1 mm. We measure the finished hole diameters at final inspection using a tapered gauge.  Microsectioning backs this up and provides more detailed information on the quality of our processes.  The next picture shows the actual width of a plated hole with nominal diameter of 250 microns.

Copper thickness

Inner layers

Inner layers are not plated so the copper thickness is that of the copper foil used.  However, some copper is lost during the cleaning processes.  The IPC A 600 Class 2 standard gives the following values for the minimum acceptable copper foil thickness after processing:

Start copper Minimum thickness after processing
12 µm 9,3 µm
18 µm 11,4 µm
35 µm 24,9 µm
70 µm 55,7 µm

This image show the copper thickness after processing for an inner layer with 35 µm start copper:

Outer layers.

Outer layers are plated up when we plate through the holes, so that the final copper thickness is the start copper foil less any copper lost during cleaning plus the plated copper.  IPC A 600 Class 2 gives the minimum acceptable finished copper thickness after processing as:

Start copper Minimum thickness after processing
12 µm 29,3 µm
18 µm 33,4 µm
35 µm 47,9 µm
70 µm 78,7 µm

Microsectioning shows the thickness of an outer layer track with 18 µm start copper:

We can also measure separately the thickness of the base copper and of the plated copper.  The base copper foil in this case was 12 microns.

Solder mask

The minimum solder mask thickness over the copper conductors should be 8 µm.

Surface finish

We can use microsectioning to measure the thickness of Leadfree Hot Air Levelling (HAL). For electroless gold over nickel (ENIG or Che Ni/Au) we can only use microsectioning to measure the nickel thickness (as shown in the picture) as the gold thickness is under 0.1 µm. For measuring the thickness of the gold and for Immersion silver we use non-destructive X-ray measurement.

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.

How Often Can You Raise a Eurocircuits PCB to Lead-free Soldering Temperatures?

Gold plating for edge connectors

Gold Plating over Edge Connectors

Eurocircuits offer two types of gold finish: Electroless Nickel Immersion Gold (ENIG) as a surface finish for the whole PCB, and hard plated gold over plated nickel for edge-connector fingers. Electroless gold gives excellent solderability, but the chemical deposition process means that it is too soft and too thin to withstand repeated abrasion. Electroplated gold is thicker and harder making it ideal for edge-connector contacts for PCBs which will be repeatedly plugged in and removed.


Technology

We plate the hard gold onto the PCBs after the soldermask process and before we apply the surface finish to the rest of the board. Hard-gold plating is compatible with all the other surface finishes we offer.

We first plate 3 – 6 microns of nickel onto the edge connector fingers and then on top of that 1 – 2 microns of hard gold. The plated gold is not 100% pure; it contains some cobalt to increase the wear-resistance of the surface.

We normally bevel the edge connectors to ensure easy insertion. Bevelling can be specified in the order details.

To make sure that the gold fingers align exactly with the edge-connector profile, we rout the vertical edges of the connector on the first drill run. The edges of the connector are then exactly aligned to the printed image.

In some cases one or more gold fingers are shorter than the rest, so that the longer pads connect first when the PCB inserted into the connector. This means that the shorter pads cannot be connected vertically to the plating bar. They have to make the connection needed for electroplating in another direction (see illustration. Here the blue lines represent the profile added at first drill stage and the green the final profiling).

After plating we check the adhesion of the plated nickel and gold with an industry-standard tape-test. We measure the thickness of the plated layers with a non-destructive X-ray measuring machine.

Limitations of the technology

  • The plated pads have to be on the edge of the PCB, as this is an electroplating process. There has to be an electrical connection between the plated pads and the production panel frame.
  • The maximum length of the plated pads is 40 mm as we use a standard shallow plating bath .
  • Inner layers have to be free of copper at the edge of PCB. Otherwise the bevelling could expose the copper.
  • If you want your PCBs delivered in a customer panel, the panel frame/border must be open on the edge connector side to allow us to make the connection for electroplating.
  • We can plate hard gold on two sides of PCB. But if the connectors are on the opposite sides of the PCB there has to be a minimum 150 mm between them.
  • To ensure optimum quality surface-finish, do not place any plated holes (PTH), SMD or other pads closer than 2.00 mm (80 mil) to the gold fingers – see drawing.

Soldermask on via-holes in case of chemical Nickel-Gold surface finish

Soldermask on via holes

There are 3 ways our customers prepare their layouts with respect to covering via-holes with soldermask:

  • Vias open (not covered by soldermask) on both sides of the PCB
  • Vias closed (covered with soldermask) on both sides of the PCB
  • Vias open from one side and covered from the other side of the PCB

As necessary background information we need to briefly introduce you into the technology of applying soldermask to the boards.


  • First we cover the whole surface of the production panel with soldermask ink and then dry the panel (printing the soldermask)
  • The ink we use is a UV sensitive material. When exposed to UV-light, the ink will harden (exposing the soldermask)
  • Ink that is not exposed remains soft and can be washed away using a 1% alkalic solution (developing the soldermask)

The easiest production method is to have all vias open from both sides. The vias will be clean. They will not contain any contamination nor soldermask. The next picture shows vias free of soldermask. We did not expose the soldermask on the via pads so that it remains soft and is washed away during the developing process.

Another practical production method is where the vias are covered on both sides of the PCB. We expose the soldermask on both sides of the via-pad and via-hole so it will harden and stay on the via-pad and over the via-hole to close it. There is a risk however that (mostly in case of via-holes with a larger diameter) the via-hole is not completely covered and a small opening remains in the middle.

There is a danger that chemicals get stuck in these small openings during the processes that follow after the soldermask application. These chemical can contaminate and affect for instance the chemical Ni/Au process. A further danger exists that chemicals of the Ni/Au process remain in these openings and as they are agressive chemicals they might keep on reacting in the via hole years after the board has been produced causing possible failures in usage of the PCB in its application.

The third case (vias covered from one side and open from the other side of the PCB) is the most problematic in production. This design creates a pocket. We expose the soldermask from one side but not from the other side. This soldermask in the middle of the via-hole will only be half polymerised. During the baking process this material can come out of the hole from the open side and contaminate the copper surface and thus disturb the surface finishing process. The pictures below shows a typical failure.

Vias and Chemical Nickel-Gold (ENIG)

Vias that are not completely covered or not properly filled with soldermask may create “skip pads” in the ENIG process.

Till now we didn”t receive any reasonable explanation from our material suppliers nor did we found one elsewhere that reveals the source of this problem. However supplier advise and long term experience guide us to two possible solutions to avoid the issue:

  • Modify the layout so that all vias are open. Our engineers favour this solution. Sadly this is not always accepted by our customers or the design may not allow it.
  • Apply the soldermask after the ENIG process. This is a costly solution as all copper surfaces are gold-plated and the soldermask adhesion becomes worse.

For closed via-holes we have developed an alternative solution which avoids chemicals getting trapped in the partially closed via-holes during developing of the soldermask or during application of the Ni/Au. Before the coating the entire panel with soldermask we selectively print soldermask into the via holes using a stencil. During a second print run we then cover the whole panel. This way the via-holes are completely filled with soldermask. An even layer of soldermask now covers the via-holes leaving no pockets to hold residual chemicals. We have used this technique for over 6 months, and it has proved successful in dramatically reducing the number of skip pad problems.

The following movies show this process of via filling and soldermask printing.

Setting up the machine:

{flowplayer}http://www.eurocircuits.com/images/stories/Movies/02_set_the_stencil_on_the_frame.flv{/flowplayer}

Printing the soldermask into the via holes:

{flowplayer}http://www.eurocircuits.com/images/stories/Movies/09_printing_closer.flv{/flowplayer}

Result after filling the via holes:

{flowplayer}http://www.eurocircuits.com/images/stories/Movies/10_result_close.flv{/flowplayer}

Cover the panel with soldermask:

{flowplayer}http://www.eurocircuits.com/images/stories/Movies/12_SM_printing_closer.flv{/flowplayer}

Result after printing the soldermask:

Drying the soldermask layer:

{flowplayer}http://www.eurocircuits.com/images/stories/Movies/13_Pre-dry.flv{/flowplayer}

Hand-soldering – point by point or mini-wave technique

Hand-soldering with the same high quality result as reflow or wave soldering?

Are you ready for the challenge ? Let us look at the mini-wave soldering technique.

This picture shows that tools and skills are the basics to achieve a good result in hand-soldering. You agree ?

Hand-soldering is in most cases the last step in the prototype assembly process. Why is it less controlled and more difficult than other steps in the manufacturing. It is something we all know how to do. It”s just heating up a PCB and a component to make a solder joint. Isn”t that simple?

PCB designers, technicians, electronics engineers, we all learned at school how to solder with an iron. It can be 5 or 35 years ago, but we assume that not a lot has changed. A lot did change!

Do we still take our car to a service where they have only mechanical hand-tools to fix it ? They do have a lot of tools these days to do a good repair job.

 


Soldering connections – Solderjoint

A good solderjoint is an electrical and mechanical connection which in the best condition is made in one shot with a temperature as low as possible, and as quick as possible. This rule is still valid, even when solder-alloys have changed from Sn63/Pb37 to the leadfree SAC305, SN100,.. or whatever the alloy used.

A good iron and the right skills makes the perfect start. What is the temperature of your iron today? How is the geometry and condition of your tip? What solder-materials do you use? Are you soldering leadfee assemblies?

 

 

Today we show you a technique to solder a SOIC-16 (Small outline Integrated Circuit 16 I/O) or PQFP-100 with Gull Wing leads. The quality we like to match is the same or even better than in a full automated production line. We all know how to solder this point by point, but do we master the Mini-wave technique?

 

 

 

 

See more details from the SOIC in the package outline

What do we need :

  • Soldering station (iron)
  • Soldertip
  • Solderwire
  • Flux past / Flux pen
  • Tweezer
  • Cleaning product
  • EPA zone ( ESD protected area)

How do we proceed:

  • Set the temperature as low as possible considering the pcb design ( layers, copper mass )
  • Insert the tip into the soldering iron
  • Heat-up the tip and check the tip conditions: the solder should flow (spread evenly) over the plated tip area.
    • If this is not the case, clean the tip surface ( to remove oxidation)
    • if this does not help, replace the tip with a new one.
  • Place the SOIC 16 on the PCB and attach 2 or 4 corners to hold the component in place ( Apply flux to the pads before placing the SOIC on the board)
  • Add flux paste or flux to all leads/pads on the SOIC16
  • Clean the solder-tip on a wet sponge or brass tip cleaner
  • Add solder to the tip-end (miniwave or conical tip)
    • Point by point soldering: {flowplayer}http://www.eurocircuits.com/images/stories/Movies/point-by-point-soldering.flv{/flowplayer}
      • Solder all leads individually – point by point by adding the right amount of solder. The solder is provided by hand using a fine solderwire.
    • Mini-wave soldering: {flowplayer}http://www.eurocircuits.com/images/stories/Movies/mini-wave-soldering.flv{/flowplayer}
      • Place the mini-wave tip ( parallel to the pads) on the first pin of the PQFP/SOIC and move along the pins at a constant speed. Solder all leads in less then 5-10 seconds.
      • Do the same thing again on the other sides of the PQFP/SOIC
  • Clean all Flux-residues with a cleaning solvent and ESD-safe trigger grip
  • Check all solderjoints/connections with a microscope/videomicroscope/magnifier.


The difference between both techniques is that the point to point technique takes much more time than the mini-wave technique. With the point to point technique it is also more difficult to have an even quantity of solder on all the joints.

 

Through hole component soldering with the eC-reflow mate

PIP (Pin in Paste) technology for soldering trough hole components

PIP is a technology for assembling through hole components using a conventional reflow soldering process. The process is also known as THTR (Through Hole Technology Reflow).

Most PCB”s that contain SMD components usually also contain some through hole components, such as connectors, switches, capacitors and so on . The principle of PIP is that through hole components are placed into PTH holes with SMT solder past and then reflow soldered with the other SMT components together.

We judge this can be a technology of interest for electronics developers that decide to assemble their prototypes themselves.

The next figure shows the process sequence we advise :

Important parameters for this process are hole and pin sizes, boards thickness, thickness and opening of the stencil , used paste printing technique and used paste.

It is obvious that only components that can withstand the reflow soldering temperatures can be soldered this way.

Most datasheets for PIP connectors also contain useful information such as the recommended stencil design.

Some hints based on our experience to give you the best results:


  • Reduce the hole size as small as possible for the component pin to be soldered
  • Avoid big annular rings
  • Do not put via holes in areas where solderpaste needs to be printed
  • Position the squeegee at an angle of 45° to the stencil to improve the pressure of the paste
  • Increase the size of stencil apertures to overlap on the area around the PTH hole (overprint) – when the solder paste melts, it will flow into the holes.

Image of the bare bottom side of the PCB after printing the solderpaste on the top side :

Cross-section of the component pin after soldering with PIP technology :

Advantages of the PIP technology

  • You can spare one step in the assembly process, this reduces cost as well as time.
  • All components are processed within one SMT solder process.
  • Good wetting and less risk for solder bridges
  • Connectors suitable for PIP generally require less board space, and are easier to repair then SMT connectors.

The Pin in Paste technology is very useful, because you can save time and manpower. We think this technology makes it easier for electronics developers to assemble prototypes in-house in a reliable, quick and affordable way.

More information about the equipment used in the test is available in our section on SMD reflow equipment