New B7971 x 4 PC Board Available

2014-12-02 08.38.47

After nearly 2 years, the B7971 x 4 PC Board is back. This new version includes an RGB LED underneath each tube. Project documentation is here.  Design docs are here. You can purchase them in the store

Picking a Pick and Place

The Autotronik BS281, Aka the Manncorp MC400

 

 Overview

A key piece of equipment in electronic assembly is the Pick and Place machine or ‘PnP’ for short.  A PnP places electronic components onto circuit boards. These days, the majority of components are about the size of a grain of rice and smaller, making hand assembly meticulous or impossible. Fully automated PnP machines with a basic set of features start at $35k. High volume, large capacity PnP machines can have price tags well north of $150k. This may seem steep, but since they are treated as something called ‘capital equipment’ by the bean-counters, you get to treat them as ‘Assets’ and ‘Depreciate’ them which, trust me, the bean-counters consider a Good Thing(tm) . The take-away is that their price tags shouldn’t give you as much sticker shock as you initially might think. For instance, if you are borrowing money from your Aunt Stella and she asks “What if you go under in a year ?”, after telling her that’s not ‘gonna happen, tell her that you can liquidate your assets and the PnP machine is likely to recover most of its value. Promise her some free assembly runs too :)

Feeder Requirements

Feeders are the parts of the PnP which supply(aka feed) components to be placed on the board. Feeders are designed for the packaging that the components are supplied in. There are many types of packaging – Loose, Tape, Tube and Tray are just a few.

Selecting a Pick and Place is driven by the size and type of components you intend to place. I analyzed some typical designs and determined my designs fit the following mix:

Part Type Footprint Packaging % of Total in Typical Design
Small Inductors, Resistors, Capacitors, Transistors, Diodes 0603,0805,1206,SOT23 8mm wide tape ~50%
Medium Inductors, Resistors, Capacitors, Transistors, Diodes, Small ICs 2420, SMB,8-SOIC, 2010 12mm wide tape ~25%
SMD Crystals, Medium ICs, 16-SOIC, 14-SOIC, Medium BGA, Leadless, SOIC 16mm wide tape ~12.5%
Larger ICs, Small Connectors, Small Electrolytic Capacitors, SOW-24, USB mini-b, Cap 10mm Radial,  BGA, Small PLCC 24mm wide tape <~3%
Larger ICs, Connectors Power Inductor 32mm wide tape <~3%
Other ICs, Modules, Connectors TQFP, Large PLCC, BGA Waffle Tray or Loose <~3%
Certain SOICs 16-SOIC, 14-SOIC, etc Tube <~3%

 

It should be noted that determining the width of the tape and the specific packaging is usually buried deep in the component data sheet and typically a big pain in the tuckus to locate. Often, the packaging is driven by the  distributor. Sometimes exact packaging cannot be predicted when ordering small quantities;

Armed with this general information our requirements for feeders are:

Waffle Tray – Highly desirable as an IC tray area can also be used for cut tape, or any part that can be laid out into a consistent X,Y array. Some parts arrive in waffle trays. Custom waffle trays can be easily laser cut. Some machines are sophisticated enough to be able to pick, align, and place parts placed randomly on the flat tray area, but this could slow down training and placement quite a bit.

Tape Feeders – As many lanes as possible. Order 8mm tape feeders in the largest number, w/some capability for 12mm. Larger 16mm, 24mm, and 32mm would be desirable but not mandatory to start off with as parts that large can be placed into trays

Tube Feeders – Desirable, but not mandatory as their functionality can be substituted by laser cutting custom waffle trays as previously mentioned.

Other Requirements

The machine should be able to place larger modules such as Wi-Fi or ZigBee radios, Leadless and BGA parts, and smaller parts below 0603 such as 0201

The Contenders

During my pre-purchase research in 4Q2012, Two machines made the shortlist (update 1Q2014: no new contenders in thsi price class):

Manncorp FVX

This machine is based off of the earlier Manncorp 7722FV machine, which originally designed and manufactured by Japanese company MDC.  This model is used by Adafruit Industries and numerous others. It is the least expensive and generally highly capable, and meets all the basic requirements

Manncorp MC-400

 

 

 

 

 

This machine is actually designed by Autotronik of Germany and manufactured in Asia. It is sold in North America by Manncorp as the MC-400. It has a high degree of commonality with the Manncorp MC-385 series, and uses the same feeders.  They are used by such companies as DIY Drones, Polulu, Spark Fun and many, many others.  While more expensive than the FVX, it uses the same smart feeders as the MC-385 series which means a very easy upgrade path to the next level.

 

Machine Comparison

FEATURE

Manncorp FVX

Manncorp MC-400

Tape Feeder Lanes

54

64

Waffle Tray Area

Yes

Yes

Tube Feeder

Yes

Yes

Max PCB/Panel Size

390 x 310mm
(Shared with Waffle Tray Area)

415×320
(Shared with Waffle Tray Area)

Placement Speed

2200 placements per hour

3000 placements per hour

Minimum Component Size

0201

01005(ridiculously tiny, BTW)

Placement accuracy

+/- .1mm

+/- .05mm

Min Lead Pitch

.4mm

.4mm

BGA, Leadless (Bottom Vision)

Yes

Yes

Feeder commonality with higher capacity machines

No

Yes

Software commonality with higher capacity machines

No

Yes

The Selection

While both machines met all of the basic requirements, the MC-400 was chosen over the FVX mainly because it provided an upgrade path to larger machines with respect to software and feeders. These features come at a higher cost, but my capital equipment budget allowed for it. That said, the FVX would also be an excellent pick for organizations on tighter budgets, and with their advanced vision capabilities, I expect both machines to postpone their obsolesence for many years to come.

Resources

I’d like to thank Adafruit Industries, Spark-fun, and Polulu for providing  great resources which helped with the selection and led to other great resources on the net. Here are some of them:

Adafruit’s 7722FV Pick and Place – http://www.ladyada.net/wiki/mdcpickandplace

Surface Mount Tech Forum – http://adafruit.com/forums/viewforum.php?f=42

 

 

How boards get tested

 

 

What happens when you forget a board in the toaster oven...

Fortunately it was an obsolete board w/no components that I was just checking solder paste batches on…

The Process of Stuffing Boards

It starts with un-packaging the parts from the supplier and placing them on a clipboard with double-sticky tape.

 

 

 

 

 

 

Next, the Kapton Stencil is taped down to another clipboard. Old PC boards are used for registration. I get the stencils  made at http://ohararp.com/Stencils.html

 

 

 

 

 

 

This is the paste I use. $<15 a syringe from http://www.zeph.com/ They also sell other solder supplies.

 

 

 

 

 

 

 

To apply the paste I just use a plastic putty knife purchased from the local big-box store..

 

 

 

 

 

 

 

An alternate method to applying with a screen is to syringe directly. This can be accomplished with an air-powered materials dispenser readily available on ebay..

Scary Robot Face or Nixie Display Board ?

I didn’t intend for it to look like a face, but it did. This is the next display board coming down the design pipe. It will support 2 IN-2 tubes. Jumpers will allow you to drive up to 3 of these boards, or a total of 6 tubes with the nixie shield, and up to 4 boards for a total of 8 tubes with the nixie driver board.

Nixie Shield ready and validated for production

 

Part of the procedure of preparing any new board revision for production is to hand-stuff one article. This is not only the best way of making sure no stupid mistakes were made, but also to make sure the list of parts you want your assembler to stuff is perfectly correct. This is also the time to follow one’s own assembly notes that will be shipped with the kit and to make sure there are no errors or omissions. Schematic, BOM, Assembly diagrams must match perfectly.

I assembled this article with an air-powered paste dispenser which is the method my assembler will use. I made sure part polarities are noted and unambiguous. I verified that the silk-screen gave adequate guidance and no misguidance.

In the end, I am happy to report there were no glaring issues. This latest batch of boards from pcbcart are high-quality. Masking vias is a good thing.

I just sent a board out to Laen which will act as a pogo-pin based test jig.

Also checked out the code. Verified it will compile with the Arduino 1.x tool chains.