A Storm in the making

A Storm In the Making

Ken takes us through the pilot manufacturing run in Shenzen along with its inevitable hiccups..

Before rushing into mass production of any new product it is sensible to carry out a pilot production run – to make sure that everything works – before you commit to the expense of full production.

My career for the last 20 years has taken me through several such pilot production runs, for various companies and individuals around the world. In many cases I was the hardware engineer on the project – and it was therefor expected that I would oversee the pilot and main roduction runs. As a consequence, I have been travelling to Shenzhen, China, many times since 1999.

Over the years, I have worked with many great people over there, who have gone out of their way to ensure that production runs smoothly, and to ease the stress of meeting tight deadlines in a very foreign country. As a result, I have made many good friends, who are willing to get involved or help out, however they can, in any new project.

The tight timescales of the myStorm Project meant that we would have to combine the Pilot Production with an immediate small run of production units, and this naturally put extra demands on time and resources. However, I am pleased to report that everything went as smoothly as expected, and we now have a batch of 50 myStorm boards heading back to the UK.

myStorm_concept
In this blogpost, I’ll try to give a flavour of some of the challenges we have faced over the run up to and then Pilot production run.

Sourcing the Components.

I needed to source at least 50 sets of components for the Pilot Production, and this was further complicated in that some of these were sourced in the UK and needed to be shipped across to Shenzhen in time for production. I then found out from a contact at RS Exports Department, that Chinese Customs were cracking down on small shipments – and as such I would be heavily penalised for import duty, or components would be delayed or confiscated in Customs. This was not what I wanted to hear, as any uncontrolled delay might jeopardise our chances of getting the goods back into the UK by Friday 2nd September.

SRAMS

My task was to source the sets of ICs that would be used on myStorm. This included the ICE40 4K FPGA and the ARM Cortex microcontroller and a couple of smaller parts.

The ICE40 was in short supply in the UK, so I had to purchase from Mouser in the USA and have 33 parts shipped across. These arrived on Thursday 11th August, and were repackaged and ready to ship on Monday 15th, along with the other ICs.

I found the Chinese Customs site very confusing – so I decided to sent the ICs to my friend Eva, in Hong Kong, so that she could fill out the necessary customs declaration in Mandarin, and choose a local courier company who could deliver the ICs across to Toby in Shenzhen.

The distance between Hong Kong and Shenzhen is barely 20 miles, but with the complication of “1 Nation 2 systems” this courier process took about 5 days to complete. Toby received all of the ICs on Monday 22nd August.

Meanwhile, Toby had been visiting the Shenzhen Electronics Market and purchasing all of the smaller items on the BOM – such as the passives, connectors, switches, LEDs etc. These items are seriously cheap in China – as most of them are locally produced, whereas ICs generally still come from Western Suppliers, and tend to have little price advantage when bought in China.

The Road to Production.

Not quite a dark Tom Hanks movie, but still with enough twists in the plot to challenge the small team we have working in China.

With the components sourced, it was time to deliver them to the pcb assembly factory- so that they could be placed on the solder pasted pcbs and run through the reflow oven.

BOM_checking

On Thursday, Toby messaged me to say that the “plate” – the foil stencil used to apply solder paste to the pads, had a problem and would have to be remade. This would cost $45 and take 24 hours. Not a huge monetary expense, but a delay in production to Friday/Saturday, leaving us just 5 days to ship the goods out of Shenzhen and back to the UK in time for the FPGA course at OSHCamp 2016.

The solder stencil arrived at the factory late on Friday, and a couple of trial pcbs were made to ensure all was well – and that the voltage regulator circuit was producing a stable 1.2V for VCC and 3.3V as the main digital supply rail. I had insisted that we do these tests before placing the expensive main ICs – that represent about $15 per board. The reason for this is that we had seen issues with the dual su[pply switcher in the prototype and wished to lower that risk.

The voltage regulator tests went well, and so I was happy to comit to the 4 panels of 12 boards to be fully populated with all components and run through the assembly and reflow process. Toby worked until 9pm Friday – to ensure everything was good to go – for an early morning start on Saturday to get the batch of boards completed.

In order that I could be online to assist – it meant me getting up very early Saturday morning – about 4am, which is 11am in Shenzhen. Toby informed me that the factory were complaining that the pads used for the 0402 components were oversize and that some of the very light 0402 components were “Tomb-stoning”. This is the process where the solder paste on 2 pad components does not melt evenly, and the surface tension effects of the first pad to melt causes the component to erect vertically – just like a tombstone.

This was not good news – and I assured Toby that I had used the standard footprints for 0402 as supplied by EagleCAD. However – this was probably where I went wrong, and should have read some of the online guides about pad sizes and preventing tombstoning.

myStorm_batch_48

Fortunately the problem was not excessive, and any components that did tombstone were easily corrected manually with a soldering iron. By 6pm Shenzhen time, the pcbs were finished and ready for collection.

sample_small

Toby and I could then relax – after what had been a long and stressful week.

Summary of additional costs:

Shipping ICs to Hong Kong from UK $85
Shipping ICs to Shenzhen plus Chinese import duty (17%) $165
New solder stencil $45
Shipping goods by DHL Express to UK

Lessons for the Future

Shipping ICs around the world often attracts additional costs of import duty – worsened if you then need to pay again when they arrive back in the UK. However because many of the ICs were sourced in the UK and US – we had no real option. Part of the way through this traumatic 2 weeks, I found out that Mouser have a Chinese Division and that almost all of the Western sourced ICs could be bought from Mouser in Shenzhen – and not attract additional charges. This will be the preferred way – moving forwards into volume production.

Because of delays in the Pilot Production, it left us little time to ship the boards back to the UK – and so a more expensive Express service had to be employed. With a little more time and a little less rushing around – this would have saved a bit of money.

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