Out of stock components just before PCB assembly

[Nikos A.]

Hi everyone,

I need you advice regarding an issue I am facing while manufacturing PCBs. Somew times and when I come into the assembly stage, I realize that some of the componnents I have choosen for my design they are not in stock any more (from Mouser, Digikey etc). So I have two options, either to wait for re-stocking based on the lead time or to re-design the PCB choosing a different part. This is very annoying and time consuming so I am looking for solutions to work around this issue.

When I spoke with Mouser, they inform me that they cannot reserve components (that's make sense). So, what I am thinking is that, as soon as I have finalize the schematic design, to place an order of my BOM and when I am ready for manufacturing to dispatch the components to the manufacturer for assemly..

How do you overcome this? Is there any standard/common procedure to follow?

Thanks in advance
Nick

[krzysssztof]

Well, there are some options:

1) As soon as you release the design, you need to buy batch of components and keep them in house
2) In your design you can use components which are very widely available or have replacements from other manufacturers
3) You are such a big player, that you can have a direct supply line from components manufacturers
4) If non of the above fits you - the only option is to wait until components will be re-stocked

[phil from seattle]

This has been an issue as long as there have been electronic products.

Manufacturers have procedures for ensuring second-sources for as many of the components as possible. There are elaborate qualification processes to ensure component availability to avoid disrupting production. It starts with the design of the board and gets drilled into many EEs heads when they start designing products. Most components get a cross reference list of acceptable replacements. Often board redesigns happen to avoid problematic parts.

What can the little guy do?
- Design with the most generic of parts where possible (603 and 805 resistors for example). If the distis have 10 equivalents, there will probably always some available.
- Avoid using highly specific or unique features where possible. Don't design your circuit around a micro that has a very specific feature, for example.
- Avoid components that might be reaching end-of-life.
- Avoid really new designs - if they don't take off the disappear beneath the waves of market pragmatics.
- Avoid single source components.  easier said than done, though.
- Use parts that are more mainstream. If there are a number of popular products with the part, it will probably be available though if a shortage looms the buyers will be locking up all the stock.
- If you expect a long production life, create cross reference lists for all your parts and keep it current. If there is a shortage, you just pick the next one on your xref list.
- Be ready to redesign your product if a shortage happens. In fact, I'd say you probably need to do this now based on your question.

Even if you do all that, shit happens - factories burn down, get flattened by earth quakes or flooded by tsunamis. So yes, maintain your own stock.  At least for the components that are critical to your product.

I have a small product that I use JLCPCB to build.  Their parts library often has shortages. I redesigned the board to use parts that they were likely to have in stock (basic vs extended) and where they had multiple same design parts. Where there were similar components, I picked the one with larger # available. (not a great metric but better than a coin toss.)  In one case, redesigned the footprint to allow a slightly different package to also be used. Every build I have done has required small redesigns or at least BOM tweaking. Never been shut out due to component shortage.

[AndyC_772]

The proper way to manage this problem is to have a good relationship with your assembly subcontractor.

They should be able to keep track of their own stock levels, any additional stock which they hold but which is specifically reserved for you, and any distributor stock that they're able to draw from.

Most importantly, they should keep track of the lead times on any critical components, and proactively warn you when it's time to place orders, so as to ensure you don't find yourself staring at a PCB with an empty site where a chip should be.

If you have good stock management, then you shouldn't run out of anything provided your usage rate is fairly predictable. If you don't, then you'll get the dreaded email which says "we can't get part X in time for this build, please can you let us have an alternative component which is an exact drop-in replacement that's available ex-stock right now".

There are pragmatic choices you can make at design time. If one variant of a microcontroller is available from stock, but another is on an 8 week lead time, pick the readily available one - even if it has more memory than you need and costs an extra 20p. Talk to your distributor, they'll know what's in full production and what only gets built to order every 6 months if you're lucky. If you can use the same parts on multiple products, then you always have the option to rob parts from one kit to fill another.

Don't redesign a PCB to use something else unless a key component is outright discontinued - and even then, a last-time buy is often a better option. Redesigns are costly in time, tooling costs, certification and paperwork - even if it's something as simple as choosing a part in a different package.

[Scrts]

The proper way to manage this problem is to have a good relationship with your assembly subcontractor.

Our hardware dept. cannot even get hold of SMT assembly line downstairs, not even talking about suppliers...

The only way to manage it is to buy the components, put it on your shelf and release the Gerbers... Then ship the components to the assembly service while PCB is being manufactured.

[kemi]

Get used to it or go higher up in the food chain.

However, there is always a way round these things. You are always going to learn to best cause of action for your components with time -- What your should tell your clients, the components that can be replaced and situations where you just have glance at the football fixtures.

[Kleinstein]

With critical (no easy replacement) components it may be the best to order the parts before finalize the order on the boards - sometime even before finalizing the PCB design. This should be no problem with small quantities - but it can be expensive (capital and some risk)  for large numbers.   

For more common parts (e.g. resistors, OPs) one may order later and prepare for a change in components if needed. There is still a small chance for sudden surprises (e.g. the MLCC shortage a few years ago when even 100 nF in 0603 could have been a problem), but there are often alternatives.

[Nikos A.]

Thank you all for your contribution!! It seems that having in stock critical components is a wise move. However, I'll take into account all of your suggestions.

Thanks

Nick

[TomS_]

Curious, what kind of parts do you have issues with?

It could be worthwhile to spend time researching what options are available from a variety of different manufacturers that share a common footprint, dimensions, function, and building a list of those similar components.

It might not be much fun to do that as it could take hours to find a couple of options for one part. But if it saves having to redesign a PCB at the last minute (which has its own dangers) and means you can get your PCBs into assembly quicker, then it is probably worth it.

[Siwastaja]

If possible, only design in parts which show good stock on multiple distributors at the same time. Having secondary part numbers for replaceable/jellybean parts really helps.

As soon as you are 100% sure the BOM won't change - the PCB layout doesn't need to be finished at this point - order the parts. This way, you can minimize the time between the decision to using a part, to actually ordering it. Have your own stock. If you don't want to stock parts yourself, discuss with your contract manufacturer about ordering the BOM before you supply the gerbers / P&P files. They likely can stockpile the parts for you.

Finally, sometimes you just have to accept that components have lead time. 26 weeks is very standard. Accept the fact that product manufacturing cycle might be half a year!! Once you are past small prototyping batches, this isn't a problem; order enough for the sales of the next half a year, and order more well in advance. Avoid designing in components with 52 weeks lead time.

If you require extensive in-house testing and qualification of parts so that you can't just choose a part and order 1000pcs a week later, good luck. You need to discuss with the manufacturers directly, and for that, you need large enough volumes.

[Mechatrommer]

1) make pcb rev2 to use different part. if the original part arrive, resume rev1 assembly
2) make breakout board for new/compatible part and use on existing pcb
3) learn from lesson. check worldwide stock count and buy part first before making pcb (even before or during design stage). its unlikely people stop making pcb, but part can dissappear. so order pcb in the last work list. means your work should according to priority (high risk first). ymmv.

[jmelson]

I need you advice regarding an issue I am facing while manufacturing PCBs. Somew times and when I come into the assembly stage, I realize that some of the componnents I have choosen for my design they are not in stock any more (from Mouser, Digikey etc). So I have two options, either to wait for re-stocking based on the lead time or to re-design the PCB choosing a different part. This is very annoying and time consuming so I am looking for solutions to work around this issue.

When I spoke with Mouser, they inform me that they cannot reserve components (that's make sense). So, what I am thinking is that, as soon as I have finalize the schematic design, to place an order of my BOM and when I am ready for manufacturing to dispatch the components to the manufacturer for assemly..

Yes, I have run into this many times.  Also, I build my own boards in small batches, so I have a few times had a mad scramble to find the last of some discontinued part when I go to build the last batch of bare boards.  i try as much as possible to use widely second-sourced parts, but that isn't always possible.  It is a constant nightmare, since I build a lot of products with very long production lives.

Jon

[S. Petrukhin]

When I encountered a delivery problem, I placed two different components on the board at the same time. For example, the photo shows two solid-state relays U45 and U67 from different manufacturers.