Metal stencil – first impression

Over the past summer I have been designing my SDI-12 data logger. So finally I was ready to send my design out to JLCPCB.com for a small batch (10 boards). I thought, why not trying out their $7 stainless steel stencil for a change? I’ve used Kapton stencils for over four years and have grown tired of the floppy stencils and frequent need to clean under the stencil while stenciling the boards. Bigger holes like crystals often leak solder paste under them and make the printing a bit messy. Overall leakage causes printing to degrade after a few board and you might have to wash it clean after a dozen boards if you can’t stand the degraded prints. Plus, alignment with Kapton stencils is not great since the film can be stretched very slightly to lose alignment across a slightly larger board (a few inches long).

Since I reviewed the quality of a batch of printed circuit boards made by JLCPCB.com in comparison with a popular PCB service a while ago, they were pretty happy with the details I went into with my favorable review and promised to print another batch of boards for free. I took the offer and asked for a stainless steel stencil. So the following story is my first impression of stainless steel stencils, which is very positive after some minor struggle. Hope it is as entertaining as it is useful.

It took me approximately one week to get the board and the stencil in a DHL envelop. Here is the package inside the DHL envelop:

It’s actually pretty big due to the large size stencil. You can make a rather large (non-framed) stencil with their $7 service. Let’s see what’s inside the package:

The package has two wood/paper/cellulose boards that sandwich the “gigantic” stencil. The stencil is protected (on both sides) by a polymer film. By the way, I used half of one of the cellulose board (probably a sacrificial base board for PCB routing) and built a home sprinkler controller on it. Details of that project will be forthcoming when I clear my backlog of “things to be posted”.

The above is a close-up. The exact side is 28cm by 38cm (11inch by 15 inch). The thickness is 0.12mm or between 4mil and 5mil, just what I wanted. My other stencils made with Kapton are only 3inch by 3inch or 5inch by 5inch. The actual stencil area is no more than 4inch by 4inch. Here is how 4*4 area looks like on an 11*15 area:

Here are the PCBs (10-qty) and a ball pen with paper stem, very environmental!

Now I have to find a good way to cut out the stencil from the whole sheet of stainless steel into something around 5inch by 5inch. I asked around online and was suggested to use a knife:

I tried several times as hard as I could with a ruler over the right side as a test but only was able to scratch a line without any hope to cut through. What was I thinking, cutting steel with steel blade? Let’s try scissors now that I have a line :

Wait a minute, let’s bend along the line to see if it breaks. LOL it won’t break! Back to scissors.

I made the cut but the edge was not flat. I can’t use this on printed circuit boards! I won’t even use these as decent shims.

I started looking for tools around my lab and office area. How about this paper cutter?

It seems to cut just fine although I need to push hard to get it started. The cut edge is flat and smooth:

A few more cuts later, just the right size (with PCB on left):

 

One things worth showing is that the surface of the stencil is not as smooth as the rest of the surface. There are fish-scale shaped marks (see the photo above for overall):

Here is the surface around a 0805 resistor under a macro-zoom lens I use for board inspection:

The reason for the fish-scale marks is that the surface has been brushed by a metal brush to remove the burr from laser cut edges. This was expected. Let’s get started stenciling. The photo also shows how nice the square corners are. The width of the pattern is a little over 0.05 inches or 1.27mm. I secured a board (black) with some older phi-panel PCBs (green):

I used a a “credit-card” squeegee with a new syringe of SAC-305 solder paste:

Here is how nice the print looks (please click and zoom in):

I’ve never see clean prints like this before! The ADS1115 (0.5mm pitch) on the top left side is super clean! And you know the end result. I posted this photo in the announcement of my data logger prototype:

I didn’t have a single solder bridge or spot that needs rework. A list of components I put on the board: ATMEGA328P-AU, ADS1115, ESP32, MicroSD card slot, DS3231, battery, crystal, LM1117-5.0, various 0805 resistors and capacitors, polyfuse, transistors (FET and BJT), and a number of thru-hole components.

So the end result was pretty darn good, for $7 extra only! My Kapton stencils of smaller sizes cost more (including shipping). I would highly recommend this stencil service if you’re already considering getting PCB from them, JLCPCB.com.

By the way, the PCB printing quality was good as well. The black one on top is from JLCPCB.com while the purple one on the bottom is from a reputable service provider in the US (guess who uses purple exclusively?). Tye quality is comparable. The pitch of the pins is 0.5mm:

JLCPCB – A new PCB fabrication house

I was recently approached by a new PCB fabrication house JLCPCB (technically they’ve been in business for some time but just started advertising to USA customers) to write some reviews on their service. Given my experience designing PCB and using PCB fabrication services (batchpcb, seeedstudio, iteadstudio, oshpark etc.) over the past decade, writing a review shouldn’t be too hard. If they are any good, I could use their service myself and recommend them to others in the hobby electronics community. So I sent them two of my designs and got them back relatively fast, with DHL. Since I still have some older versions of one of the boards, I could make a comparison with the two fabrication services. JLCPCB has offered their service free of charge for the exchange of a fair review. So I decide to not mention which competition I pitched JLCPCB against. What I primarily looked at was how accurately each layer of board is printed and how well they are aligned with one another from each fab service. JLCPCB‘s results are very good. Its competition, a long-standing name among DIYers, doesn’t look quite as good.

In case you’re still learning how to design PCBs, especially surface-mount components, here are some terms I’m going to use:

Top layer: this logic layer contains all copper traces, pads, and vias on the top side of the two-sided circuit board. A process is used to protect all aforementioned features specified in this layer when the entire board is etched in acid. If the process isn’t accurate, then your features aren’t exactly where they are supposed to be.

Top solder paste: this logic layer contains only pads for surface-mount components. It is a subset of top layer and is used to generate stencils for reflow soldering. Again if the fabrication isn’t very good, these features tend to not align with other features.

Top solder resist: this logic layer contains similar information to the pads and vias contained in top layer but the sizes of the features in this layer are slightly enlarged to a peel-back amount so they don’t accidentally apply solder resist on top of your pads where solder should go. Solder resist is a lacquer that prevents solder from adhering to the copper traces. They also protect the bare copper from rusting away. You will want them to be applied to all your traces and only leave the pads exposed so later process will cover them with a very thin layer of solder (the shiny looking stuff) and you then reflow solder your components to these pads. If the registration of this layer of lacquer is not well registered with the top layer, you will see visually under a magnifier. This is why fabrication houses usually do quite a bit of peel-back so they leave room for themselves to be less-aligned but still the lacquer won’t cover up the pads.

The following images are from an FTDI chip (FT232RL). The pitch was the finest on my board so I selected these pads for comparison of how well the different layers register with one another on these two service providers.

Top: JLCPCB Bottom: competition


They look similar. I’ve unfortunately scratched the pads on the competition’s board. I applied solder paste to that board and later cleaned the paste off so I could photograph its pads. My bad.
On a closer look there is a difference:

SMD pads (SSOP 0.65mm pitch):

Top: JLCPCB Bottom: competition
You can see that JLCPCB‘s boards (top) have SMD pads (shiny metal pads) that are very symmetrically situated inside the solder-resist masks (slightly larger dark rectangle). The solder resist also goes closer to the board than its competition. These are manufactured from the same designs! The engineers at the competition must have increased the peel-off (sizes of feature not covered by solder resists) to offset their less-perfect layer registrations and/or accuracy on each layer. As you can see, not all pads and their solder resist have the same offset. Some look better than others. This is clear with the second to the last pad and the last pad. The pads are not centered at all. This is very consistent across the board made by competition. JLCPCB has better overall registration than competition. Better registration translates into better chance to prevent solder bridges and less chances to reworking on your boards after you reflow them, that means time and money saved.

Thru-hole pads (o.1″ spacing):

Top: JLCPCB Bottom: competition

The top one has less size solder resist layer, the edges of the red lacquer surrounding the shiny pads (almost same size as the thru-hole pads) and very symmetrical. The competition has again increased the solder resist layer and couldn’t keep the layer registered well with the pad.

The via to the right of the bottom right through hole pin hole will be compared next. On JLCPCB‘s board, its solder resist has 2.8mm diameter when displayed on my computer monitor. On the competition board, it is 3.1mm. The images were taken under a high-magnification lens and I checked the images to be exactly the same zoom, measuring the same across the same features on screen. What this means is that if you have a lot of vias in one area, very close to one another, you may get some solder bridges between the vias if there is not enough solder resist to separate them. Not a problem on this board but a problem if you happen to have vias very close and also close to thru-hole components. You solder the thru-hole and inevitably fill the adjacent vias with some solder. This could short vias.

Overlay (white texts):

The quality of the white overlay texts are about the same between the two fabricators, although at some places you see one board having better quality than the other board while at different places the quality is reversed. This is not a crucial feature to look at though.

JLCPCB: top, Competition: bottom

With the explanation above, you can easily distinguish these two photos. The bottom one has so much space between the edges of the shiny pads and the red lacquer (less qualty). The top one has so much less and so symmetric.

So the results are clear. JLCPCB is a pretty decent PCB fab house and I will order my next batch from them. The shipping cost is also slightly less than competition if you use DHL. I always use DHL. They do a good job delivering to small cities like the one I live in!

Here is a link to JLCPCB’s website:

www.jlcpcb.com

I am not getting any commissions for your purchases. The link has no “trackers” 🙂

P.S.: I had a research student hand solder this board (yes, every single chip resistor and the FTDI chip) as a good test of his skills and it turned out fine. This is a proof that having the right size solder resist helps, really. This is what the board looks like after assembly:

Ordering PCB from seeedstudio

Here is the updated tutorial:

https://liudr.wordpress.com/2017/05/26/ordering-pcb-from-seeedstudio-com/

This is a short tutorial on how to order your PCB from seeedstudio.com

I am not associated with seeedstudio but just a regular customer. They have competitive price and decent quality. They also recently automated design file submission process, although there is still some kinks.

Once you finish designing your PCB with EAGAL CAD, you should use seeedstudio’s CAM file to export the design into several files. The CAM exports many files but only the following are useful and should be zipped in a .zip file, per their sales page:

  • Top Layer: pcbname.GTL
  • Bottom Layer: pcbname.GBL
  • Solder Mask Top: pcbname.GTS
  • Solder Mask Bottom: pcbname.GBS
  • Silk Top: pcbname.GTO
  • Silk Bottom: pcbname.GBO
  • Drill Drawing: pcbname.TXT

Once you have a .zip file, direct your web browser to seeedstudio.com  and you will see their store front:

1

Once you are on their web store, look for “Services” on the navigation bar on the left and click it. It will bring up their services page, with three types of service.

2

The second one “Fusion PCB Service” will take you to their online PCB ordering page. Click “Fusion PCB Service” and you will see the following page:3

There are a lot of options on this page. I will list what they are below:

  • File: Pick the .zip file that contains your design. I have two zip files, Shield_V1.0.5.zip, and Power_supply_V1.0.2.zip. I will select Power_supply_V1.0.2.zip
  • Qty: Seeedstudio doesn’t make 1 PCB, the least amount is 10 PCBs. Go ahead and pick 10, unless you want 50 or 100.
  • Layer: You will pick 2 layers. This means you will have circuits both on top and bottom of your circuit boards. I don’t see many single layer PCB any more but they were popular decades ago.
  • PCB Thickness: Go ahead and pick 1.6mm. Most popular thickness is 1.6mm. If you want some added mechanical strength on your larger boards, you can go with 2.0mm.
  • PCB Dimension: This is the maximal size of your PCB. Typical sizes they provide are 5cm*5cm (about 2″*2″) for $10 (10 boards), and 10cm*10cm (about 4″*4″) for $25 (10 boards).
  • PCB Color: You can leave this as Green since other colors cost extra $10-$20. It’s just the look. Your PCB will be painted with color paint.
  • Surface Finish: Pick HASL (Hot Air Surface Leveling). It’s a technique that plates holes with hot molten solder and the excess is removed by hot air. You can also pick leadless HASL if you want to go green. You may upgrade to ENIG, which is Electroless Nickel Immersion Gold. Holes will be covered by a thin layer of gold to prevent oxidation.
  • E-Test: For somewhat sophisticated designs, E-testing is recommended. For something simple such as the power supply board, it’s not very necessary.

Say I have two designs, Shield_V1.0.5.zip, and Power_supply_V1.0.2.zip. I will first select Shield_V1.0.5.zip in the file selector, select everything according to the list explained previously (Qty=10, Layer=2, Thickness=1.6mm, Dimension=10cm*10cmColor=Green, Finish=Hasl, E-test=100%),  then push “Add to Cart”.

Then I will push “continue to shop” and be brought back to the PCB ordering page. I will pick Power_supply_V1.0.2.zip and select 5cm*5cm. Similar settings to the other design (Qty=10, Layer=2, Thickness=1.6mm, Dimension=5cm*5cmColor=Green, Finish=Hasl, E-test=50%) and add to cart. I’m not testing these boards 100% since they are simple.

4

After everything is added to cart, I would proceed to check out. You need to set up an account with seeedstudio and have a paypal account. Shipping is less than $10 but slow. I average about 3 weeks between design submission and delivery (to Mid-west, USA). You can also pay DHL and save maybe a week or more, although I never used it. I guess that’s it. Well, one bug on their site though: if you select a design zip file and push add to cart, but later remove the item from the cart, you can’t upload the same file anymore. I guess they buffer your file but don’t remove them when you remove your item from cart. You will have to change the name of the zip file if you do encounter this problem. I’m sure they’ll fix it soon.

Oh by the way, since you’ve read this far, I’ll tell you a secret or two:

  1. If you order $50+ at their store, they ship for free.
  2. If you order 10, you will likely receive 11 or even 12 boards. If you order 50, you probably get 51. Sometimes it’s cheaper to order 10 PCS the same design from time to time than ordering 50 pcs, since you get 10%-20% more boards and only like 2%-4% more boards with 50 PCS 😉

New Arduino shield – Phi-1

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I have developed this shield in my spare time to make prototyping with Arduino much easier. The shield, when assembled, has one LCD monitor, 6 buttons, real time clock and battery backup for keeping time, EEPROM for data storage, GPS connector, buzzer, LED, and two RJ11 connectors for things you absolutely want secured against pull.

Here is a video of a 360 degree view of an assembled Phi-1 shield:

Just running a clock with DS1307 Real Time Clock (RTC) module

Running a testing routine to make sure everything works

Running a fully-functional alarm clock (it woke me up this morning) Details of making the alarm clock is on a separate post. The code is listed near the end of this post.

Morse encoder: type in a sentence and translate it into Morse code.

Function list:

  • 16X2 LCD character display
  • 6 push buttons –  four arranged in arrow keys and two more on the side
  • 2 RJ11 ports for long and robust connections with sensors or control devices
  • Optional buzzer and LED in place of the RJ11 ports
  • Real time clock with battery backup keeps the time when Arduino is turned off
  • EEPROM for easy data logging keeps data when Arduino is turned off. Use 24LC256 or compatible I2C EEPROM
  • GPS connector and breakout for this popular GPS module (http://www.sparkfun.com/commerce/product_info.php?products_id=465)
  • Reset button for Arduino
  • All Arduino pins are brought out for maximal flexibility.
  • Hackable for more functionalities (see the end of the assembling)

 Possible projects with this shield:

  • Alarm clock
  • Standalone or PC data logger
  • Lab data acquisition system (Physics, Chemistry etc)
  • Weather station
  • Input or operating panel, like security panels or garage door opener
  • Handheld GPS
  • Morse code generator
  • The list goes on… 

Documentation:

Phi-1 shield documentation revision 11/19/2010

PCB design:

Schematic:

Fully assembled shield running clock:

 

PCB and parts:

Connector board design pictures:

Standard board breaks out connections from the RJ11 jack and 5V/GND. The prototype space has 5V/GND running down middle for convenience. You can make a TTL-RS232 circuit on it, or maybe power an opamp, add I2C A/D converter to it or else. The screw terminals are pretty convenient and their connections are brought out for prototyping. You can also simply plug it into a breadboard. It also has two LED indicators and has connections for X, Y, 5V and GND.

The relay board has a standard AC or DC relay with control signal coming through the RJ11 jack from the main board. Several screw terminals are included for wiring. A power jack is also included so that it can easily power a single piece of equipment with the relay. You can turn on and off an electromagnetor else light with it. 

This board passes the RJ11 connection to a 3.5mm stereo plug. It also has an LED indicator.

Assembling pictures:

Sample codes:

Clock display This is a basic program that displays the Clock. You can modify it to suit your needs.

Testing all functions This program tests everything, LCD, buttons, the clock, and EEPROM if you have one on board. Learn the basics of everything with this program.

Alarm clock (buzzer and LED) This program is a fully-functional alarm clock. You will find it more complex than the basic clock. If you can’t understand, try the Click display first.

Morse encoder This program allows you to type in a sentence in letters, numbers, and symbols. Then it plays it in Morse code. Use the arrow up and down to type letters (think old-school arcade game record) use left and right to move cursor. Use B to enter.

More to come!

I am coordinating an effort to have it made in a small quantity so it will be affordable. If I have one made, it will cost me around $30, but if I have more made, I could cut the cost down and possibly have it for $12. Leave me a message if you’re interested in getting one. I might be able to get my favorate electronics online store to sell these so you could buy the board along with all needed components in one purchase.


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