Moisture has the ability of destroying complex PCBs quietly – and simple visual aids can usually thwart such a loss. Humidity indicator cards provide a cheap and instant visual check of the interior of dry packs allowing engineers and quality departments to determine whether a board has been exposed to harmful moisture in either storage or transit. To prevent the expensive rework we recommend this check on arrival and before assembly.
Why Moisture Matters for Multilayer PCBs
Multilayer boards are multilaminated copper, prepreg and substrate boards. Absorption of moisture leads to reduced insulation resistance, the onset of ionic migration and the brittle behaviour of solder joints during thermal cycling. The addition of a Humidity indicator card with each moisture-barrier bag provides instantaneous exposure feedback at the point of sale to allow QA to correct the situation prior to assembly or shipping.
How Visual Indicators Help QA and Logistics
A humidity indicator PCB Card can show whether a dry pack has been compromised during transport. Since not all indicators are reversible, they leave traces of an event that occurred due to humidity and decrease argument in terms of acceptance testing. In long supply channels or other products sensitive to climate like automotive radar PCBs, that permanent record assists in quicker and safer choices on either baking and declining a lot.
Practical Packaging and Handling Steps
Three realistic checks reduce the risk of moisture: controlled drying and baking where required; desiccant choice that is proportional to bag volume and the storage period; packing completed boards in moisture-shield bags made of metal in plastic with a Humidity indicator card in each inner bag.
In the case of cavity and two-depth PCBs, seal integrity is of particular concern – closed-up cavities are more humid and require a stronger desiccant and indicator plan.
Why Type 2 (Non-Reversible) Indicators Are Recommended
The trend in industry is towards Type 2 indicators, which are non-reversible indicators of SMD dry-packs. An example of such a device is the humidity indicator PCB Card (Humitector Type 2) which eliminates cobalt dichloride and provides a permanent 60% RH signal without sacrificing any reversible lower-RH spots to check the functionality. That combination assists manufacturers to abide by the IPC/JEDEC dry-pack practices and satisfy the audit requirements of procurement.
Product Descriptions and Budgeting Figures
The threat of moisture is minimized by three realistic controls, including controlled drying and baking where needed; desiccant selection that is proportional to bag size and the storing time; putting finished boards into moisture-shield bags of in. plastic with a Humidity indicator card in each inner bag.
Cavity integrity and two-depth PCBs Seal integrity is of special concern in the case of closed-up cavities – the former is more humid and needs a more vigorous desiccant and indicator plan.
Sizing Desiccants and Checklist Items
Calculate desiccant mass using ingress of moisture expected to enter the bag and length of stay. Check bag permeability, pick the desiccant grams per bag, place a visual HIC in the inside pack and capture an image of the lot. These are useful measures that avoid most moisture failures without redesigning boards.
A modest desiccant plus a visual indicator often prevents a single costly rework event on high-value assemblies. Validate with your yield data.
Procurement Checklist
Request suppliers to verify written confirmation of indicator model, type of desiccant and bag material. Add acceptance criteria in purchase order and seek sample packs to be verified. A brief supplier audit or sample test on arrival will save time and stop replacement of less accurate indicators.
Integrating Indicators into Production
On the floor we take a Humidity indicator card to the inner pack, take a photograph of the lot number to be made at the job ticket, and place that image on the job ticket. When a humidity sensor PCB Card indicates exposure in excess of the selected limit, the batch is put under drying, reflow simulation testing and specific electrical testing.
This minor administrative measure eliminates huge downstream failure expenses and makes warranty investigations less cumbersome.
Training, Traceability and Procurement Notes
Train operators to read spot colours, to record readings and to label any bag that has changed spot. In your BOM, specify the specific indicator model, e.g. humidity indicator PCB Card Type 2, to avoid being replaced with generic and less precise cards.
Photo and lot number traceability helps in saving time of investigations in case of anomalies.
FAQ
Q: What are reversible cards and what are non reversible cards?
A: Routine monitoring with reversible cards; non-reversible Type 2 cards (as recommended by IPC guideline) required in situations where you require a lasting record of a serious exposure.
Q: What is the estimation of desiccant size?
A: Corresponds to the weight of desiccant in grams with the weight of the bag internal volume and the anticipated storage time; to prevent rework increase desiccant size when there is a long storage time.
Next Steps
We are constructing moisture control in our production and packing checklists at BS Interconn. Get in touch with our team to discuss packaging, get supplier quote or to design the correct humidity indicator PCB Card and desiccant pairing to use in your project
. Request a free packaging estimation and quote with the supplier. We are able to make automotive, telecom and industrial board recommendations.