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What to do with a pre approved stack up that needs alterations?

The choices you take when designing you PCB in these challenging material and production lead times, can have serious impact on the delivery of your printed circuit.
Written by: Jan Pedersen, 
Senior Technical Advisor

It’s fall, we have passed our second COVID summer, and the world is slowly looking more “normal”. However, things are most definitely a bit different these days.

Recently I got an order, just like every day. The designer had spent the last 3 weeks completing the design and got it approved for order placement.

Next step in the flow is when the purchaser spends a few days to get prices right, and then the order can be placed.

Anything wrong with this? 

No, business as usual to make sure the design is correct and prices are negotiated to save money. Everyday operation in this industry.
However, in a normal year, with normal material lead times, and without escalating material prices, that is how it works.

Today things are a bit different!

Let me elaborate on an example from the last few weeks.

I was contacted by a designer requesting a stackup for an 8 layer PCB. A quite standard stackup that could work for most 8 layer designs. Meaning that he would need impedance per design, but not controlled, no microvia and no critical thickness requirements.

But, this designer always requests a stackup including the exact materials used, to match his lines to the stackup.

Basically, this stackup works for most 8 layer designs, even for those with impedance lines. As long as we don’t change the track, gap and stackup, it will work.

After this he spends 2-3 weeks on the design. After one week he was more or less done, but had the design sent for verification before he closed it and submitted it to procurement.

What then when the stackup is pre-approved but needs changes?

The purchaser received the gerber files and submitted his request for quotation to 2-3 of his most trusted PCB suppliers. He got the first quotation within 8 hours, but decided to wait another 2 days to make sure he had the best price.

Order placed as usual, but now things started to happen.

The PCB factory replied that the material supplier for this brand and type suddenly had 8 weeks lead time. He sent back an Engineering Query for alternative materials that would keep the stackup and those designed impedance lines.

Designer rejected; the stackup had been approved by the end customer – no chance to change it now! So, what happens next?
EQ is sent back to the PCB supplier, with the result of a 5-6 weeks increased lead time compared to the original offer.

So, why am I telling this, and what can we learn? 

First of all, in a normal situation this is not necessarily an issue, but today with increased and less predictable material lead times, and on top of that unpredictable material prices, we need to adapt to the situation and be smart.

How, I guess you wonder?

First of all, make sure the stackup and material selection is as open as possible.

  1. Don’t lock your stackup to one material brand or type of material. Allow for factory standard materials to be used.
  2. Try to use IPC 4101 slash sheet numbers, unless you have special needs.
  3. If you have impedance lines designed in, make sure to describe what you need. The factory will in 99% of the cases be able to tune track and gap to meet their standard materials.
  4. If you ask for a factory stackup, make sure you allow standard materials to be used.

Also consider releasing the stack up for material to be allocated, or even placing a material preorder.

By these actions, you can simplify the process of approving the design, and, as we currently face an unpredictable material situation, avoid sudden increased material lead times from stack up is approved, and up to order placement.

Remember that the PCB factory doesn’t order material before all EQs have been closed, adding on another 2-7 days.

Is price the key to success, or are other parameters also vital?

We all know price matters when procuring printed circuits. Some buyers only target on price, benchmarking and swapping suppliers more often than the Kardashians shoot selfies. Long term relationships might sound boring, but also offer predictability, priority and dual source if needed. Just to specify, I am only talking about relationships with your PCB supplier.

In a market like today a few pennies saved can be at a high cost. My advice after decades in the industry and facing its current challenges daily, is:

  1. Place the material allocation order as early as possible – as soon as the stackup is fixed.
  1. Don’t start negotiation prices and lead times the day you expect to place the order – it is too late! Not even the same week.
  2. Select a trusted supplier that accepts material allocation on orders and stay with him.
  3. Work on long time trust and be predictable within the nature of your business.

When it sounds too good to be true, it most often is. Go realistic.

The last thing I want to mention is the need of a PCB supplier that has skills and knowledge to guide you in the right direction.

As in all matters of life, procuring printed circuits is also about finding solutions. We aim to guide our customers in a material selection, available within reasonable time. Finding solutions that combine function and availability is vital.

Today the best direction is not necessarily to meet all the customers’ needs, finding special materials or processes, but maybe all of this in combination with a realistic view of what can be done, within a reasonable time.

All up to last autumn we did not have this understanding. Today it is vital to reach the market in time. My Senior Technical Advisor colleagues and I, aim  to maintain the attitude of: “Nothing is impossible, we will find a solution”.

That is still true, and in 90% of the cases it’s possible. However, “the material availability ghost” is haunting all in the industry every day, which means we also need to use all our skills and knowledge about material lead times to find good solutions for the customers, and maybe most important, realistic and reliable solutions!

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Grensen 12, N-0159 Oslo
Norway (Google maps)

Phone: +47 22 09 87 00
Fax: +47 22 22 03 25 921 513 240 /
DUNS nr. 519297139

Grensen 12, N-0159 Oslo
Norway (Google maps)

Phone: +47 22 09 87 00
Fax: +47 22 22 03 25 921 513 240 /
DUNS nr. 519297139

Part of NCAB Group

Grensen 12, N-0159 Oslo
Norway (Google maps)

Phone: +47 22 09 87 00
Fax: +47 22 22 03 25 921 513 240 /
DUNS nr. 519297139

Grensen 12, N-0159 Oslo
Norway (Google maps)

Phone: +47 22 09 87 00
Fax: +47 22 22 03 25 921 513 240 /
DUNS nr. 519297139


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