FR4 Single-sided PCB (244x256mm) 1.2mm thickness warp

[ngkl99]

Hi,
i am facing problem with pcb warpage (>1.5mm) at initial condition.
Any novel solution?
I tried, different cavity direction, add/remove copper, but still fail.

Thanks!

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here is the image of my board

 

[barry]

When you say "at initial condition" do you mean right from the PCB manufacturer? Or after soldering?

What is your soldering process? If you're getting a big temperature gradient that might cause the board to warp.

You could use board stiffeners.

 

[ngkl99]

Hi Barry, thanks for the reply
Initial condition means from the manufacturer (blank board).
Soldering process is reflow (lead free solder)...
board stiffeners / pallette is not preferable by production because cost reason...
headache..
thanks!

 

[ngkl99]

currently this board has solder mask at one side of board only,
i am thinking whether solder mask at both side will improve the board or not.
means : A side: copper and solder mask
B side: no copper, but have solder mask

 

[barry]

1) I seriously doubt solder mask can fix warping.
2) If the board comes from the manufacturer warped, why aren't you complaining to the manufacturer???? They have a specification on warpage, is the board within that spec?

 

[ngkl99]

hi Barry, our members went to the PCB maker site, they found the boards were within specs.
Usually maker will send to us immediately after the PCB has been made.
But when the boards reached us, it was warped.

 

[marce]

How many layers how much copper on each layer copper weight

 

[ngkl99]

hi marce,
single-sided pcb with 1/2 oz copper...

 

[marce]

3.4.3 Bow and Twist Unless otherwise specified in the
procurement documentation, when designed in accordance
with 5.2.4 of IPC-2221, the printed board shall have a
maximum bow and twist of 0.75% for boards that use surface
mount components and 1.5% for all other boards. Panels
which contain multiple printed boards which are
assembled on the panel and later separated shall be
assessed in panel form.
Bow, twist, or any combination thereof, shall be determined
by physical measurement and percentage calculation
in accordance with IPC-TM-650, Method 2.4.22.

The IPC-6012 guideline on bow and twist. I have seen this problem with single sided boards in the past, but do so few single sided boards these days and very rarely the size you have. With reference to the spec above there can be up to 3.4mm bow for a PTH board and 1.7mm for a SMD board. What worries me is what will happen to the board during soldering!
There are two courses you can take:
Liaise with you manufacturer and see if there is anything they can do.
Go double sided and create a balanced laminate.

Marc

 

[Mattylad]

Talk to your manufacturer, ask them why it is warped.

Reject the boards.

 

[ngkl99]

The problem is before soldering process, the board warps more (initial condition).
Soldering process only slightly increase the warp value...
can't go for double-sided because cost up...

 

[barry]

1) The manufacturer sends boards to you.
2) They are warped when you receive them.
3) You reject the boards.

Why is this so difficult? I mean, you get a defective part and you want us to tell you, what, exactly?

 

[ngkl99]

to find the root cause...

 

[barry]

to find the root cause...

As stated by another poster, this is a problem for your PCB manufacturer. THEY are doing something wrong. If they can't find the problem, get another manufacturer.